Alfredo Alexander-Katz, Massachusetts Institute of Technology
Matthias Schneider, Boston University
Ting Xu, University of California, Berkeley
HH3: Supramolecular Assembly I
Juan de Pablo
Tuesday PM, April 07, 2015
Park Central Hotel, 3rd Floor, Cornell
2:30 AM - *HH3.01
A Molecular View of Equilibrium and Non-Equilibrium Directed Assembly in Molecular and Polymeric Systems
Juan de Pablo 1 Paul Nealey 1
1University of Chicago Chicago United StatesShow Abstract
Directed copolymer assembly (DCA) has emerged as a promising alternative for patterning at sub-lithographic length scales. Much progress has been made over the past decade, but a number of significant challenges remain. Our recent efforts at the University of Chicago have focused on development of a molecular based, multiscale computational modeling approach aimed at gaining a fundamental understanding of directed copolymer assembly on nanopatterned substrates. This presentation will begin with a brief overview of available theoretical and computational approaches, along with a discussion of their advantages and limitations. That overview will be followed with a description of recent modeling advances that have enabled quantitative descriptions of time-dependent, morphological evolution during various physical processes. The applicability of the models will be discussed in the context of assembly of block polymers doped with nanoparticles, patchy particles, and liquid crystals, which are found to alter the phase behavior and dynamics of these systems considerably.
3:00 AM - HH3.02
Self-Sorted Multicomponent Low Molecular Weight Hydrogels
Dave J. Adams 1 Catherine Colquhoun 1 Louise Serpell 2 Kyle Morris 2 Lin Chen 1
1University of Liverpool Liverpool United Kingdom2University of Sussex Brighton United KingdomShow Abstract
Controlling the order and spatial distribution of self-assembly in multi-component supramolecular systems could allow us to prepare new functional materials. A challenge is to produce generic and controlled ‘one-pot&’ fabrication methods to allow the formation of separate ordered assemblies from mixtures of two or more self-assembling species, which might have relatively similar molecular structures and chemistry. We show here that self-sorting in low molecular weight hydrogels can be achieved using a pH triggered approach [1,2]. The assembly conditions for each molecule are pre-programmed on the basis of their pKa.
We show here that this method can be used to prepare gels with different types of mechanical properties. Cooperative, disruptive or orthogonal assembled systems can be produced. We demonstrate this conclusively using a range of techniques. Gels with interesting behaviour can be also prepared. For example, by judicious choice of gelators, self-sorted gels can be prepared where there is a pre-determined, delayed switch-on of gelation. Co-assembled structures can also be generated, which leads to synergistic strengthening of the mechanical properties. Finally, we also discuss some unusual cases, for example where mixing leads to two non-gelling molecules forming a gel.
 C. Colquhoun, E.R. Draper, E.G.B. Eden, B.N. Cattoz, K.L. Morris, L. Chen, T.O. McDonald, A.E. Terry, P.C. Griffiths, L.C. Serpell and Dave J. Adams, Nanoscale, 2014, DOI: 10.1039/c4nr04039b
 K.L. Morris, L. Chen, J. Raeburn, O.R. Sellick, P. Cotanda, A. Paul, P.C. Griffiths, S.M. King, R.K. O&’Reilly, L.C Serpell and D.J. Adams, Nature Commun., 2013, 1:1480
3:15 AM - HH3.03
Microfluidic Reactors for Mesoscale Bio-Inspired Supramolecular Functional Materials
Lawrence Valverde 1 Amanda Marciel 1 Charles Schroeder 1 William Wilson 1
1University of Illinois at Urbana-Champaign Champaign United StatesShow Abstract
The mesoscale engineering of nanoscale building blocks holds enormous promise to catalyze a revolution in new functional materials for advanced energy technologies and other applications. Bio-inspired systems can play a key role in this effort due to their inherent capacity for combining multiple components individually tailored for specific functions. Certain peptide chains possess the remarkable ability to form robust amyloid fibers that hold great promise provided that these fibers can be engineered in a controlled manner. Peptides can be combined in myriad combinations for tailored structural control and can be used to package cores such as pi-conjugated rings designed for desired functionality. Novel microfluidic reactors in conjunction with oligopeptides created from a library of various peptide residue and core combinations have recently been developed. The development of these reactors opens new possibilities for functional supramolecular materials.
In this work we will explore the use of controlled hydrodynamic flows for the directed assembly of synthetic peptides in microfluidic devices as a path to new functional materials. This strategy offers mesoscale compositional and structural control of the assembled materials, in a repeatable fashion, with the potential for scalability. We capitalize on tailored laminar flow dynamics and peptide precursor reaction kinetics to bias assembly of peptide monomers into nanoscale and larger constructs. Specifically, planar extensional flow serves to align reaction products by virtue of the differential velocities to which polymers are subject as they are assembled from their constituent peptide precursors. This hydrodynamic assembly method holds strong potential to enable fabrication of assemblies and hierarchical constructs that cannot form spontaneously in solution.
3:30 AM - HH3.04
Mechanically Tunable Optical Properties of Cold-Worked Semi-Crystalline Polymers with Long Polyalkenamer Chains
Seok Bin Hong 1 Tae-Hyung Kang 1 Woong-Ryeol Yu 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Semi-crystalline (SC) polymers generally show the necking phenomenon by cold-work above their glass transition temperature. Polymer chains in the necked region of SC polymers become aligned in a fibril structure, accompanying increased crystallinity and sometimes crazes. These two phenomena make such polymers opaque by different refractive index between void and aligned polymer chains. In this study, we report on a new finding that SC polymers such as dicumyl peroxided (DCP) cured polycyclooctene (PCO) show transparent behavior to visible lights upon cold-work.
Since transparency on cold-worked regions is not common in SC polymers such as polyethylene or polypropylene, the transparent behavior of cold-worked (cured) PCO implies that there is special molecular or supramolecular structure formed by long polyalkenamer chain with trans/cis double bond. In this study, microstructural changes of PCO upon cold-work were investigated using in-situ wide-angle x-ray scattering (WAXS), small angle x-ray scattering (SAXS) and polarized light microscopy. The crystallinity and crystalline structure of PCO upon cold-work were analyzed using in-situ WAXS by varying scanning temperature. Arrangements of crystallites and lamella in nanometer scale were characterized through SAXS 2-D imaging. Polarized light microscopy was used for observing supramolecular structure of PCO samples in micron scale.
The molecular configurations behind the transparency of SC polymers upon cold-work were revealed from the combined experiments above. The spherulite structure was deformed and destroyed under cold-work process through WAXS and SAXS data analysis. Long chain with cis- double bond is not crystallizable because of its non-linear shape. As a result, chains with cis-double bond entangles with aligned trans-double bond chains forming optically isotropic region, which can not be observed for polyethylene with shorter monomer chains and better packing property. This localized and entangled regions exhibit better transparency than gathered spherulites formed in original or heat-worked PCO samples. Mechanically tunable transparency can be imparted to SC polymers using the new finding. In addition, cured PCO exhibits shape memory properties and can be utilized as a smart polymer with both shape memory and tunable transparency.
3:45 AM - HH3.05
Thermoresponsive Ruthenium-Polymer Nanocomposites for Catalytic Production, Storage and Controlled Release of H2 in Water
Enass K. Abo-Hamed 1 Oren Scherman 2
1University of Cambridge Cambridge United Kingdom2University of Cambridge Cambridge United KingdomShow Abstract
Hydrogen is becoming increasingly important in green energy solutions around the globe, yet it is still challenging to produce, store and release the hydrogen gas in a controlled manner. We demonstrate a simple approach for the preparation of thermoresponsive porous polymer-ruthenium nanoparticle composite materials that catalytically produce and store hydrogen gas at room temperature, and its inherent thermoresponsiveness, which allows for “on-demand” release of the stored gas.
The catalytically active ruthenium nanoparticles are embedded into the polymer in a dynamic fashion by exploiting a versatile host-guest system based on the macrocycle cucurbituril. The materials demonstrate reproducible behavior over many cycles and the catalytic activity and release temperature are easily modulated by the formulation.
4:30 AM - *HH3.06
Supramolecular Micelle Networks: Computer Modeling of Equilibrium Properties and Dynamics
Elena Dormidontova 1
1University of Connecticut Storrs United StatesShow Abstract
Supramolecular polymers have attacted considerable attention by researchers over the last decade. This interest arises from the enormous potential of these materials for applications due to their versatile properties and self-healing dynamic nature. One of the expanding areas of research is supramolecular networks based on metal-ligand, complemetry hydrogen bonding motifs or a combination of both. Typically these reversibly associating units are attached to linear or branched polymers (spacers), so the crosslinking occurs either via 3:1 ligand-metal ion compexation or via binary reversible associations (or 2:1 ligand-metal complexation) connecting branched spacers. A somewhat different type of supramolecular network composed of diblock copolymer micelles interconnected by means of 2:1 ligand-metal complexation has been recently explored experimentally. These systems possess two levels of self-assembly: 1) self-assembly of diblock copolymers into micelles and 2) reversible inter-micelle bridging by coordination bonding between metal ions and ligands attached to the corona of nanoparticles, which controls their viscoelastic properties. This hierarchical self-assembly results in complex dynamics for these systems. While the large-scale properties of these materials can be successfully characterized experimentally, it is much harder to achieve molecular-level details of their self-assembly and relaxation processes. Computer modeling can be very useful in achieving this purpose. We use a combination of Monte Carlo and Molecular Dynamics simulations to gain understanding of the molecular mechanisms of self-assembly of supramolecular networks formed by diblock copolymer micelles upon metal-ligand complexation and its transformation under shear, respectively. Using Monte Carlo simulations we investigate whether metal-ligand complexation affects diblock-copolymer micelle formation and vice versa. We analyze the extent of intra- and inter-micelle loops and bridges formed by metal-ligand complexation in connection with the degree of network crosslinking and elastic properties of the network. The effect of polymer concentration, hydrophilic block length, metal to oligomer ratio and type of complexation (2:1 or 3:1) will be discussed. In the framework of non-equilibrium molecular dynamics simulations we investigate the evolution of supramolecular micelle network subjected to shear flow. The change in micelle shape, size and extent of crosslinking as a function of shear rate will be discussed in relation to the system viscosity. Computer modeling results will be compared with available experimental data and implications of the obtained results for design of future responsive materials based on supramolecular micelle networks will be outlined.
5:00 AM - HH3.07
Exotic Nanoparticles with Block Copolymer Solution Construction with Kinetic Control
Darrin J. Pochan 1
1University of Delaware Newark United StatesShow Abstract
Kinetic pathways and long temporal stabilities of different micelles and nanoscale aggregates have been used to construct exotic nanoparticles in solution. Due to low chain exchange dynamics between block copolymer micelles and solvent, global thermodynamic equilibrium is extremely difficult, if not impossible, to achieve. However, by taking advantage of this slow kinetic behavior of polymeric micelles in solution, one can purposely produce multicompartment nanoparticles and mulitgeometry nanoparticles by forcing different block copolymers to reside in the same nanoscale structure through kinetic processing. While kinetically trapped in common nanostructures, local phase separation can occur producing compartments and surface patches uniquely displayed from the surface of the nanoparticle. This compartmentalization can be used within common micelle geometries to make complex spheres and cylinders or can be used to make new nanostructures such as multigeometry aggregates such hybrid cylinder-sphere aggregates, disk-cylinder nanoparticles, and hybrid inorganic-block copolymer nanoparticles. Finally, inter particle nano structures can also be made through hierarchical assembly of exotic, multicompartment/mulitgeometry particles through adhesive or reactive patches on particle surfaces. The kinetics of the assembly process as well as the kinetics of the aging process through which nanoparticle structure evolves will be a focus of the presentation as will be the nanoscale characterization of the nanostructure and the assembly process.
5:15 AM - HH3.08
Tuning Nanostructure Dimensions via Supramolecular Pathway for An Appropriate Cell-Material Response
Sungsoo Seth Lee 1 Shantanu Sur 2 Samuel I Stupp 1
1Northwestern University Chicago United States2Clarkson University Potsdam United StatesShow Abstract
Shape effects of supramolecular assemblies on cells and within animals have been investigated previously, but only by changing the chemical composition of the materials. This inevitably remains as an additional parameter that cannot be accounted for, yet little or no effort has been made thus far to resolve it. Therefore, it is of great interest to be able to craft a range of supramolecular architectures from a pool of identical monomers. Recently, pathway selection in self-assembly has gained increased attention due to its influence on the nature of the final nanostructures. Among many, pH of the aqueous environment can greatly affect the nanostructure dimensions. Using a model peptide amphiphile (PA) molecule, we demonstrate here that a pH-induced transformation from wide to narrow nanoribbons is allowed with Na+ ions, but disallowed with Ca2+ ions. Mechanistically, divalent metal coordination stabilizes beta-sheets and enhances intermolecular cohesion within the PA assembly. Interestingly, albeit equal concentration of identical monomers, a gel network of the wide ribbons exhibits higher rigidity than the narrow ribbons. When utilized as synthetic extracellular matrix to encapsulate neural precursor cells, we find that the wide ribbon matrix promotes significantly higher neuron differentiation relative to the narrow ribbon matrix. In addition to pH, self-assembly can vary with other conditions including time, concentration, temperature, solvent, etc. Hence, the approach described here outlines a potential strategy to stabilize the supramolecular nanostructure at a given point along the pathway, allowing for a fine-tuning of the cell-material response.
5:30 AM - HH3.09
High Fidelity Infrared 1-D Photonic Crystals via Brush Polymer Self-Assembly
Robert J Macfarlane 2 Harry A. Atwater 1 Robert Grubbs 2
1California Inst of Technology Pasadena United States2California Institute of Technology Pasadena United StatesShow Abstract
Brush block copolymers (BBCPs) enable the rapid fabrication of self-assembled 1D photonic crystals with photonic band gaps that are tunable in the UV-Vis-IR, where the peak wavelength of reflection scales with the molecular weight of the BBCPs. As a consequence of the difficulty in synthesizing very large BBCPs, however, the fidelity of the assembled lamellar nanostructures drastically erodes as the domains become large enough to reflect infrared (IR) light, which severely limits their performance as optical filters. To overcome this challenge, short linear homopolymers can be used to swell the arrays to up to ~180% of the initial domain spacing, allowing for photonic band gaps up to ~1410 nm without significant opacity in the visible, demonstrating improved ordering of the arrays. Additionally, the blending of BBCPs with linear random copolymers enables functional groups to be incorporated into the BBCP array without the need to attach them directly to the BBCPs. Such functional groups should prove useful in generating functional reflective films, such as dynamically responsive photonic crystals, or films with nanoscale ordering that can be aligned with applied fields. The addition of short, linear polymers to the brush block copolymer arrays therefore allows for a facile means of both improving the self-assembly and optical properties of these materials, as well as adding a route to achieving films with a greater amount of functionality and tailorability, without the need to develop or optimize the processing conditions for each new brush polymer synthesized. Due to their ease of fabrication, reflectivity at long IR wavelengths, and lack of opacity in the visible portion of the spectrum, these polymer-based nanostructures should prove useful in fabricating highly reflective transparent coatings for structures to prevent thermalization of IR light and thereby combat the urban heat island effect.
5:45 AM - HH3.10
Nanoporous Thin Films with Contollalbe Nanopores via Supramolecular Assembly of End-Functionalized Polymer Blend
Giyoung Song 1 Richard Hahnkee Kim 1 Dhinesh Babu Velusamy 1 Jinseong Lee 1 Minkwan Shin 1 ChooJin Park 1 Cheolmin Park 1
1Yonsei University Seoul Korea (the Republic of)Show Abstract
Supramolecular assembly via complementary interaction between molecular subgroups belonging to phase-separating polymer species offers a great opportunity, not only for constructing nanoscale soft templates reminiscent of conventional block copolymer morphologies, but also for tailoring surface properties by facile removal of one of structure components via cleaving complementary interactions. We report the domain size-tunable nanoporous templates, based on utilizing supramolecular assembly of end-functionalized dendrimer with multi-arms and homopolymer under solvent-annealing. By controlling the number of end-functional groups of dendrimers as well as the molecular weight of homopolymers, domain size of thin nanoporous template films evolved in combination with the benzene/water co-solvent vapor annealing, was successfully controlled. The film of end-functionalized polymer blends yielded phase-separated nanodomains resembling nanoscopically ordered structures of block copolymer but more advantageous due to easily cleavable links between phase-separated domains by removing the one of the component of the precursor structure. The resultant domain-size tunable multi-leveled organic nanoporous films with tailored surface functionality offer a useful platform for various chemical and biological applications. We have previously demonstrated that a binary blend system, composed of mono-sulfonated polystyrene (SPS) and mono-aminated poly(ethylene oxide) (APEO) is successfully utilized to generate nanoporous templates in thin film condition. However, the difficulty in controlling their nanoscale morphologies still remained as an issue. To overcome this limitation and control the domain size, we employed a new supramolecular assembly of amine-functionalized dendrimer with multi-arms (APEO-G) and SPS. By controlling the number of end-functional amines of dendrimers as well as the molecular weight of SPS, we were able to tune domain size of thin nanoporous template films ranging from mainly 34 to 54 nm, even to 131 nm. Furthermore, our supramolecular assembly system has an advantage of easy introduction of the functional active sites to the pore surfaces by simple solvent etching process for the chemically active polymer nanotemplate.
(1) Song, G.; Cho, S. M.; Jung, H. J.; Kim, R. H.; Bae, I.; Ahn, H.; Ryu, D. Y.; Huh, J.; Park, C. Chem. Eur. J.2012, 18, 15662-15668.
(2) Huh, J.; Jung, J. Y.; Lee, J. U.; Cho, H.; Park, S.; Park, C.; Jo, W. H. ACS Nano 2010, 5, 115-122.
HH1: Supramolecular Composites
Tuesday AM, April 07, 2015
Park Central Hotel, 3rd Floor, Cornell
9:30 AM - HH1.01
Emergent Electrical Properties Induced by Guest Molecules in Metal-Organic Frameworks
A. Alec Talin 1 Michael E. Foster 1 Francois Leonard 1 Kirsty Leong 1 Catalin D. Spataru 1 Vitalie Stavila 1 Mark D. Allendorf 1
1Sandia National Laboratories Livermore United StatesShow Abstract
Metal-Organic Frameworks (MOFs) are supramolecular, nanoporous materials that self assemble in solution from metal ions and electron-donating organic “linker” molecules. Although intensely investigated for applications such as gas storage, MOFs have received little attention as electronic materials because most are insulators, due to poor charge transfer between the metal ions and linkers. We recently discovered, however, that infiltrating MOF pores with guest molecules capable of binding to the framework metal ions can dramatically alter the electrical properties. For example, redox-active TCNQ molecules bridging copper dimers in the MOF HKUST-1 create a pathway for charge transport, increasing the electrical conductivity by seven orders of magnitude. In this presentation, we discuss the conductivity mechanism and show that other emergent properties, such as thermoelectric behavior, can be achieved. These results suggest that “Guest@MOF” represents both a new class of electronic materials and a versatile strategy for creating nanoporous conductors with tunable properties.
10:00 AM - HH1.02
Photoresponsive Materials Using Metal-Ion Coordination
Giuseppe E Giammanco 1 2 Anton O Razgoniaev 1 2 Dayana A Muizzi 1 2 Christopher T. Sosnofsky 2 Jonathan D Mase 2 Alexis D Ostrowski 1 2
1Bowling Green State University Bowling Green United States2Bowling Green State University Bowling Green United StatesShow Abstract
We are interested in exploiting transition metal-coordination in polymer systems, creating photo-active metallopolymers. Our current approach is to use transition metals Co3+ and Fe3+ coordinated to polymers like polysaccharides and polyamines. The transition metal ions allow for new photochemistry in which the bonding interactions and polymer cross-linking can be controlled with light.
Photoresponsive Fe(III)-polysaccharide materials were created that showed changes in mechanical properties after light irradiation. There were unexpected differences in the photoreactivity in the materials due to structural differences and stereochemistry of the polysaccharides. These photoresponsive Fe-coordination materials have also been used to create small hydrogel capsules capable of carrying a cargo inside the gel network. Controlled release of the cargo was achieved by light irradiation of the hydrogel capsules.
Other metallopolymers were created by coordination of Co3+ with polyamines. These materials showed changes in mechanical properties depending on the mole fraction of Co3+ added. In addition, the Co(III)-polyamine materials exhibited self-healable properties, where cuts in the material could be repaired. Future work will focus on tuning the photoreactivity and mechanical properties of these metal coordination materials using different transition metal ions and polymers.
10:15 AM - HH1.03
Electrically Conductive Networks for Li-S Redox Flow Batteries
Laura C. H. Gerber 2 Peter D. Frischmann 2 Sean Doris 2 Erica Y Tsai 2 Frank Fan 1 Yet-Ming Chiang 1 Xiaohui Qu 2 Anubhav Jain 2 Kristin Aslaug Persson 2 Brett Anthony Helms 2
1MIT Cambridge United States2Lawrence Berkeley National Laboratory Berkeley United StatesShow Abstract
Redox flow batteries require conductive additives to efficiently transport charge between the current collectors and the active materials. Carbon blacks are currently utilized in this capacity, but they have several drawbacks, including limited charge transport kinetics, and their network formation is not well understood or controlled. We have designed molecular species that self-assemble into networks that function as conductive additives in solution-based Li-S batteries. Several compounds have been synthesized in order to access a range of redox potentials and network-forming characteristics. The compounds that form networks in the presence of Li-polysulfides show significant improvement in battery capacity in comparison to no conductive additive or to compounds with similar redox potentials that do not assemble into networks. In order to understand the network formation of these conductive materials, they have been interrogated at different states-of-charge with and without Li-polysulfides by optical spectroscopy and small angle x-ray scattering.
10:30 AM - HH1.04
A Highly-Ordered 3D Covalent Fullerene Framework
Norma K. Minar 1 Kun Hou 1 Christian Westermeier 2 Markus Doeblinger 1 Joerg Schuster 1 Fabian Hanusch 1 Bert Nickel 2 Geoffrey Ozin 3 Thomas Bein 1
1University of Munich (LMU) Munich Germany2University of Munich (LMU) Munich Germany3University of Toronto Toronto CanadaShow Abstract
Fullerenes, a family of hollow cage-shaped carbon molecules, have inspired remarkable interdisciplinary research activities in the last two decades, involving several fields of chemistry, physics and materials science. We report on a novel, highly ordered periodic mesoporous fullerene framework that is entirely constructed from individual silane-functionalized fullerene building blocks and whose mesoporosity is controlled by cooperative self-assembly with a liquid-crystalline block-copolymer.
In principle, fullerene building blocks can be functionalized at many points, potentially resulting in an enormous multitude of possible fullerene adducts with different symmetry and number of functionalities. This would lead to a complicated co-self-assembly behavior between the precursor and surfactant, and likely to limited order in the final product. To address this challenge, we surmised that a C60 hexakis-derivative with high Th symmetry would be beneficial for the construction of a porous framework.
The new fullerene framework material was obtained in the form of supported films by spin-coating the synthesis solution directly on glass or silicon substrates, followed by a heat treatment. The fullerene building-blocks co-assemble with a liquid-crystalline block-copolymer to produce a highly ordered covalent fullerene framework with orthorhombic Fmmm symmetry, accessible 7.5 nm pores and high surface area, as revealed by gas-adsorption, NMR spectroscopy, small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). We also note that the 3D covalent fullerene framework exhibits a dielectric constant significantly lower than that of the non-porous precursor material.
10:45 AM - HH1.05
Janus Lipid Self-Assembly: Evidences of Co-Existing Mesophases in a Stable Multicompartment Nanoparticle
Nhiem Tran 1 3 Xavier Mulet 1 Adrian Hawley 3 Charlotte Conn 4 Lynne Waddington 5 Calum John Drummond 2
1CSIRO, Manufacturing Flagship Clayton South MDC Australia2RMIT University Melbourne Australia3Australian Synchrotron Clayton Australia4RMIT Melbourne Australia5CSIRO, Manufacturing Flagship Parkville AustraliaShow Abstract
Janus particles with distinct regions of different functionalities have previously been observed in inorganic and polymeric systems. We present the first evidence of multiple, thermodynamically stable, co-existing lyotropic liquid crystalline mesophases within a single nanoparticle. To generate multiple mesophases, increasing amount of capric acid was added to nanoparticles of monoolein. Small angle X-ray scattering (SAXS) revealed the formation of various mesophases, including inverse bicontinuous cubic (primitive (P) and double diamond (D)) and inverse hexagonal phases (HII). SAXS analysis confirmed several compositions where mixed scattering signals were observed from co-existing cubic phases (P/D) or a cubic phase co-existing with a hexagonal phase (D/HII). A theoretical model was developed to visualise the possible interconnected nanostructures of co-existing mesophases. The model demonstrated the possible connection of two mesophases via the (111) plane. Cryogenic transmission electron microscopy (cryo-TEM) was used to obtain visual proof of the multi-compartment Janus nanoparticles. Nanoparticles with mixed phases of P/D and D/HII were identified using cryo-TEM. The lattice parameters of the identified mesophases were calculated from Fast Fourier Transformation of cryo-TEM images. These values were compared to the SAXS data to confirm the identity of the mesophases. In summary, this study provided the first evidence of stable co-existing mesophases in a lipid nanoparticle. These multicompartment nanoparticles can lead to development of smarter and more complicated nano materials with controllable functionality.
HH2: Biomimetic Materials
Tuesday AM, April 07, 2015
Park Central Hotel, 3rd Floor, Cornell
11:30 AM - *HH2.01
Mechanical Features of Noncovalent Molecular Interactions in Mussel Byssal Proteins and in Self-Assembling Mussel Mimetic Polymers
Devin Barrett 2 Grace Bushnell 2 Suresh Manohar 2 Dominic Fullenkamp 2 Phillip B. Messersmith 1
1University of California, Berkeley Berkeley United States2Northwestern University Evanston United StatesShow Abstract
Marine organisms rely on adhesive secretions for attachment to substrates in wet, turbulent environments. In the case of mussels, adhesion is mediated by the byssus, a remarkably strong and tough tissue comprised of a collection of collagenous protein threads terminally anchored by an adhesive pad. Byssal proteins form a complex self-assembled mechanical system to meet the challenges of adhesion in the wet marine environment. The amino acids histidine (His) and 3,4-dihydroxy-L-alanine (DOPA) are emerging as key elements of these proteins. DOPA is found in particularly high concentration in several interfacial proteins, where it is believed to play an important adhesive role. In the bulk, interactions of transition metals with DOPA yield coordination bonds that function as dynamic, sacrificial noncovalent cross-links that serve to increase the toughness of the tissue. His is found in byssal collagen proteins that self-assemble to form the byssal thread cores. N- and C- terminal regions of byssal collagens are rich in His, where formation of strong noncovalent interactions with transition metals (e.g. Fe, Zn and Cu) may take place to enhance the mechanical performance of the tissue. In this talk I will provide an overview of these and other molecular biomechanical aspects of mussel adhesion, with an emphasis on bulk and interfacial interactions of DOPA and His. Finally, examples of bioinspired polymer systems will be provided to illustrate how these concepts, along with self-assembly, can be exploited to develop novel materials with interesting physical properties.
12:00 PM - HH2.02
Biophysical Characterization of Reflectin Isoforms from Squid and Cuttlefish
Long Phan 1 Ward G. Walkup 1 David D. Ordinario 1 Yegor Van Dyke 1 Alon Gorodetsky 1
1University of California, Irvine Irvine United StatesShow Abstract
Cephalopods are well known for their remarkable camouflage abilities; they can modify their coloration, texture, pattern, and reflectivity to blend into the surrounding environment. Such dazzling camouflage abilities are partially enabled by specialized intracellular nanostructures that are composed of a unique structural protein known as reflectin. We have developed high throughput protein expression and purification strategies for the isolation of reflectin isoforms from the cephalopod species L. pealei and E. scolopes.1 We have performed extensive biophysical characterization of these proteins, discovering that they possess common yet unique self-assembly, optical, and electrical properties, including protonic conductivities that are on par with state-of-the-art artificial materials.2 Our findings may hold implications for better understanding the mechanisms that cephalopods employ to dynamically control their coloration and for the continued development of functional supramolecular materials inspired by cephalopods.
1. Phan, L.; Walkup IV, W. G.; Ordinario, D. O.; Karshalev, E.; Jocson, J.-M.; Burke, A. M.; Gorodetsky, A. A. Adv. Mater.2013, 25, 5621-5625.
2. Ordinario, D. O.; Phan, L.; Walkup IV, W. G.; Jocson, J.-M.; Karshalev, E.; Hüsken, N.; Gorodetsky, A. A. Nat. Chem.2014, 6, 596-602.
12:15 PM - HH2.03
From Natural to Bioassisted and Biomimetic Artificial Water Channels
Mihail Barboiu 1
1Institut Europeen des Membranes Montpellier FranceShow Abstract
This paper discusses the incipient development of the first artificial water channels systems. We include only systems that integrate synthetic elements in their water selective translocation unit. Therefore, we exclude peptide channels because their sequences derive from the proteins in natural channels. We review many of the natural systems involved in water and related proton transport processes. We describe how these systems can fit within our primary goal of maintaining natural function within bio-assisted artificial systems.
In the last part, we present several inspiring breakthroughs from the last decade in the field of biomimetic artificial water channels. Within this context, imidazole derivatives have demonstrated selective water conduction properties thanks to their propensity to form imidazole-quartet, geometrically reminiscent to the G-quartet which is able to transport cations. Water transport across bilayer membranes incorporating I4#8729;H2O has been proved. On the other hand, the bola-amphiphile triazole, TCT self-assembles to form stable T-channels in lipid bilayers and transports cations. Like in gramicidin A channels, the carbonyl moieties, pointing toward the T-channel core are solvated by water. The constitutional self-assembly process results in pore-forming structures (barrel-shaped) generating cationic transport. A crystal structure of TCT could be obtained showing four double-helix entities tightly interacting and resulting in the formation of T-channels. Possible self-assembly of T-channels for increasing TCT concentrations in contact with bilayer membrane were postulated.
These systems have provided excellent reasons to consider that chirality and water induced polarization generating dipolar ion-pumping channels may in principle to be strongly associated. The molecular-scale hydrodynamics of water within simple artificial water channels can be determined more easily than using complex biomolecules. The result of the fast transport of water through the channels has important practical applications, since ultrapure water for biomedical or nanotechnology applications will be needed like for other chemical separations using conventional membranes. All these examples demonstrate how the novel interactive water-channels can parallel biomolecular systems. At the same time these simpler artificial water channels offer a means of understanding the molecular-scale hydrodynamics of water for many biological scenarios.
1. Agre, P. Angew. Chem. Int. Ed., 2004, 43, 4278-4290.
2. Le Duc, Y.; Michau, M. ; Gilles, A. ; Gence, V. ; Legrand, Y.-M. ; van der Lee, A. ; Tingry, S. ; Barboiu, M. Angew. Chem. Int. Ed. 2011, 50, 11366-11372.
3. Barboiu, M. Angew. Chem. Int. Ed. 2012, 51 11674-11676.
4. Barboiu M. ; Gilles, A. Acc. Chem. Res., 2013, 46 (12), pp 2814-2823.
5. Barboiu, M. et al. Nature Comm. 2014, 5, 4142. DOI: 10.1038/ncomms5142
12:30 PM - *HH2.04
Assembly and Dynamics of Supramolecular Materials
Samuel I Stupp 1
1Northwestern University Evanston United StatesShow Abstract
Supramolecular materials created with components that self-assemble into ordered structures have enormous potential to create novel properties and functions in soft matter. These materials contain supramolecular components formed by self-assembly that can take many shapes including those of nanoscale fibers, tubes, ribbons, and particles. The possibility to design the non-covalent interactions among monomers allows facile integration of chemical functionalities and the opportunity to tune their dynamic properties. Tuning bonds among monomers can introduce strategies to control mechanical properties, transport, biodegradation, self-healing properties, and capacity to respond to external stimuli. This lecture will describe measurements of their complex dynamics using electron paramagnetic resonance, and also examples of their potential functions as materials for medicine and energy.
Alfredo Alexander-Katz, Massachusetts Institute of Technology
Matthias Schneider, Boston University
Ting Xu, University of California, Berkeley
HH6: Dynamics and Mechanics of Soft Materials II
Wednesday PM, April 08, 2015
Park Central Hotel, 3rd Floor, Cornell
2:30 AM - *HH6.01
Harnessing Biomimetic Catch Bonds to Create Mechanically Robust Nanoparticle Networks
Balaji V.S. Iyer 1 Victor V. Yashin 1 Anna C. Balazs 1
1University of Pittsburgh Pittsburgh United StatesShow Abstract
Using computer simulations, we investigate the mechanical properties of a network of polymer-grafted nanoparticles (PGNs) that are interlinked by labile “catch” bonds. In contrast to conventional “slip” bonds, the life time of catch bonds can potentially increase with the application of force (i.e., the rate of rupture can decrease). In effect, the bond becomes stronger under an applied force (if the strain rate is sufficiently high). Subjecting the PGN networks to a tensile deformation, we find that the networks encompassing catch bonds exhibit greater ductility and toughness than the networks interconnected by slip bonds. Moreover, when the applied tensile force is released, the catch bond networks exhibit lower hysteresis and faster relaxation of residual strain than the slip bond networks. The effects of the catch bonds on the mechanical behavior are attributed to transitions between two conformational states, which differ in their sensitivity to force. The findings provide guidelines for creating nanocomposite networks that are highly resistant to mechanical deformation and show rapid strain recovery.
3:00 AM - HH6.02
Understanding the Forces that Drive Growth of Crystalline Nanostructures by Particle-Based Assembly
Dongsheng Li 1 James J. De Yoreo 1 Kevin Rosso 1
1Pacific Northwest National Lab Richland United StatesShow Abstract
Non-classical particle-based growth processes such as oriented attachment (OA) naturally lead to formation of complex nanostructures. Thus understanding the controls on this formation pathway will enable the design of nanostructures with controlled morphology, defect structure, and tailored properties. The objective of this study is to understand the forces that drive OA and the factors that control them. . The hypothesis is that attachment is due to reduction of surface energy and the driving forces that bring the particles together are a mix dipole-dipole interactions, van der Waals forces, and Coulombic interactions. Therefore they can be controlled via pH, ionic strength (IS), and ionic speciation. We are testing the hypothesis and investigating the controls by directly measuring the interfacial force between crystal surface planes. We are employing AFM-based dynamic force spectroscopy (DFS) to measure the forces between mica, calcium carbonate, and zinc oxide crystal planes. We attach 5 to 10 µm in diameter single crystals of CaCO3, mica, and ZnO to the AFM tip and preform DFS on single crystal substrates as a function of orientation. Initial measurements of the forces between (104) planes of CaCO3, (001) crystal basal planes of mica, and (001) planes of ZnO show that the forces have strong relationship to pH, IS, and crystal orientation.
3:15 AM - HH6.03
Light-Controlled Molecular Zippers based on Azobenzene Polymers
Christopher Weber 1 Tobias Liebig 1 David Bleger 2 Juergen Rabe 1 Stefan Hecht 2 Stefan Kowarik 1
1Humboldt University of Berlin Berlin Germany2Humboldt University of Berlin Berlin GermanyShow Abstract
In this study we investigate the kinetics and mechanics of a light-induced phase transition in a photoresponsive supramolecular material. We report that spin-casted thin films of polymers with molecular switches incorporated in the backbone and interdigitating alkyl side chains (‘molecular zippers&’) can be switched reversibly with light between a semicrystalline and an amorphous state, corresponding to a closed and open state of the molecular zippers. The thin film structure and morphology before and after irradiation with UV-light is investigated with atomic force microscopy and grazing incidence x-ray diffraction. Simultaneous time-resolved x-ray diffraction and optical spectroscopy measurements show that the kinetics of the amorphization of the crystalline domains is about 12 times slower than the photoisomerization of the azobenzene switches. Our findings suggest that the amorphization is triggered by E-Z isomerization of a small amount of azobenzene chromophores within the polymer film and that the slower kinetics of the photoinduced amorphization is determined by structural and topological constraints and not by a different isomerization mechanism of azobenzene in crystalline domains. Our results are important for research areas like self-healing materials or micromechanical devices.
3:30 AM - HH6.04
Size Effect and Odd/Even Alternation in the Melting of Self-Assembled Single and Stacked Silver Alkanethiolate Layers: Nanocalorimetry Measurements and Phenomenological Model
Zichao Ye 1 Lito P de la Rama 1 2 Liang Hu 1 3 Mikhail Y Efremov 4 Leslie H Allen 1
1University of Illinois at Urbana-Champaign Urbana United States2SanDisk Corporation Milpitas United States3Intel Corporation Chandler United States4University of Wisconsin - Madison Madison United StatesShow Abstract
In biological studies, aliphatic lamellae are employed as model system for cell membranes that are composed of single layer phospholipid with bi-layer structures. We report a systematic study of the melting of silver alkanethiolate (AgSCn) lamellar crystals with supramolecular structures. A new self-assembly synthesis method enables us to control the thickness of the crystals by either modulating alkanethiol chain length (n = 7minus;18) or stacking them to a specific layer number (m = 1minus;10). Lamellar crystal structures are characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Nanocalorimetry shows stepwise increase in the melting point, Tm, of single layer AgSCn as an increment of chain length. Layer stacking also results in a size-dependent melting. An odd/even alternation is observed in the Tm of 2, 3, and 4-layer lamellae, but absent in that of single and multilayer samples. We develop a phenomenological model for lamellae melting based on the cumulative excess free energy contributions of four spatially separate regions in AgSCn crystal: free surface, Agminus;S central plane, sample-substrate interface, and interlayer interface. Surface excess free energy is revealed to be independent of chain length. The selective appearance of the odd/even effect is due to the dramatic stabilization of interlayer interfaces of odd-chain samples, possibly due to registration/packing. Interface stabilization occurs most significantly for the mobile lamellae situated close to the free surface, and thus 2-layer samples show the highest degree of stabilization. Such layer-number-dependence of interface energy is not observed in lamellar polyethylene. XRD results support the model as the measured van der Waals gap is 0.35 Å smaller for crystals with odd chains.
1. L. P. de la Rama, L. Hu, L. H. Allen, et al., Anomalous Transitions of DODAB Using Fast Scanning Liquid Calorimetry, Thermochimica Acta, 522, 72 (2011)
2. L. P. de la Rama, Z. Ye, L. H. Allen, et al., Size Effect and Odd-Even Alternation in the Melting of Single and Stacked AgSCn Layers, JACS, 135, 14286 (2013).
3. L. Hu, L. P. de la Rama, L. H. Allen, et al., Synthesis and Characterization of Single-Layer Silver Decanethiolate Lamella, JACS, 133 (12), 4367 (2011).
HH4: Self-Healing Materials
Wednesday AM, April 08, 2015
Park Central Hotel, 3rd Floor, Cornell
9:30 AM - *HH4.01
Self-Healing Supramolecular Polymers in Action
Anton Bosman 1
1SupraPolix Eindhoven NetherlandsShow Abstract
Sophisticated polymeric materials with “responsive” properties, such as self-healing, are reaching the market. Supramolecular polymers benefitting from hydrogen bonding interactions between the macromolecules, have been employed as self-healing materials. The quadruple hydrogen bonding ureidopyrimidinone (UPy) unit is a particularly effective and versatile design motif for this, since it forms very strong, yet reversible linkages, and it can be incorporated into a broad range of polymer backbones on an industrial scale, leading to supramolecular materials with unprecedented rheological responses such as self-healing. In this presentation, supramolecular polymers modified with the UPy-unit will be presented, and their self-healing applications related to coatings, adhesives, solid objects, and hydrogels, will be highlighted and discussed.
10:00 AM - HH4.02
Towards the Development of Self-Healing Semiconducting Isoindigo Polymers
Bob C Schroeder 1 Zhenan Bao 1
1Stanford University Stanford United StatesShow Abstract
Isoindigo based semiconducting polymers have been used in organic field effect transistors (OFET) achieving hole mobilities of over 3.5 cm2/Vs. Similarly spectacular are their performances in organic photovoltaics (OPV), where isoindigo polymers achieved power conversion efficiencies (PCE) of around 7% in bulk heterojunction devices and over 4% in all polymer solar cells. Furthermore isoindigo polymers proved useful for sensing applications in marine environment and was also used more recently as semiconductor in stretchable transistors. So far isoindigo based semiconducting polymers proved extremely versatile and useful in a variety of applications, however with the introduction of flexible and potentially wearable electronics, the materials susceptibility to externally induced physical damage becomes more important. Continuous bending and stretching could lead to crack formation in the polymer film, leading to a loss in performance and a significant reduction in device lifetime.
Self-healing polymers on the other hand exhibit the ability to repair induced damages or defects in their structure, ultimately restoring the materials mechanical and physical properties. Even though self-healing polymers are known for some time, most approaches developed so far are not entirely compatible with the specificities of π-conjugated semiconducting polymers.
In this paper we will lay out our design approach towards self-healing semiconducting polymers comprising the isoindigo motif. We will discuss how we achieved to lower the glass transition temperature of the polymer without compromising its semiconducting properties, leading to improved flow properties ultimately allowing the healing of externally induced damage to the material.
10:15 AM - HH4.03
New Properties of Bio-Inspired Catecholamine Films: Adhesive Self-Healing Sealants Formed at Liquid/Air Interface
Younseon Wang 1 Haeshin Lee 1 Seonki Hong 1 Stanislav Gorb 2
1KAIST Daejeon Korea (the Republic of)2Kiel University Kiel GermanyShow Abstract
Catecholamines are ubiquitously found in many organisms such as adhesive pads in mussels, beaks in squids, melanins in human, cuticles in insects, and many others. It has been found that Insect skins, the cuticle, are made by catecholamines crosslinking their cuticle proteins, and human melanin has been studied for a long time for its chemical scavenging effect of skin cancer. Recently, catecholamine has newly attracted attention in the field of the material science as a material-independent surface modification agent. The surface modified with dopamine and norepinephrine, which are both catecholamines, have been applied to various fields, including drug delivery systems(e.g. hydrogels), biomedical sciences(e.g. imaging), energy storage(e.g. Li-air battery), microfluidics(e.g. sensor) and so on. However, even though catecholamine chemistry has been used widely, all previous demonstrations aiming for the catecholamine surface modification has occurred at the solid/liquid interface. In this presentation, we report a new chemistry of the catecholamine at the liquid/air interface instead of at the solid/liquid interface. Film is formed at the liquid/air interface when polyethyleneimine(PEI), an amine-rich polymer, and dopamine are both mixed. The interfacial film has a few unique properties: First, the film consists of distinct two domains; the air-contacting top side of the film is poly(dopamine)-rich hydrophobic domain and the underneath layer facing to the liquid is PEI-rich hydrophilic one. Thus, the film has a Janus-face structure in which the upper poly(dopamine)-rich side is a flat, solid-like thin-film, and the opposite side is also a flat yet porous one. This anisotropic structure allows functioning as an actuating film, which exhibits a stimulus responsive folding behavior. In a dry condition, the porous, PEI-rich area is dehydrated resulting in inward directional folding, whereas in a wet (or humidified) condition, the PEI-rich region is hydrated causing outward directional folding. This process can be repeated for many times. Surprisingly, the film also shows a self-healing property when the underlying solution covered by the interfacial film is re-exposed to air by peeling the film a part. The self-healing can be repeated virtually unlimited times until all underlying catecholamines are oxidized or the solution is dried out. The study of the new interfacial chemistry of catecholamine at the liquid/air interface can make a big impact in the field of the material science.
10:30 AM - *HH4.04
Metal-Coordination: Using Another One of Naturersquo;s Tricks to Assemble New Soft Materials
Niels Holten-Andersen 1
1Massachussetts Institute of Technology Cambridge United StatesShow Abstract
Growing evidence supports a critical role of metal-coordination in soft biological material properties such as self-healing, underwater adhesion and autonomous wound plugging. Using bio-inspired metal-coordinating polymers, initial efforts to mimic these properties have shown promise. In addition, with polymer network mechanics dictated by coordinate crosslink dynamics, material properties can now be easily tuned from visco-elastic fluids to elastic solids. Given their exploitation in desirable material applications in nature, metal-coordinate crosslinking provides an opportunity to advance synthetic polymer materials design. Early lessons from this pursuit are presented.
HH5: Dynamics and Mechanics of Soft Materials I
Wednesday AM, April 08, 2015
Park Central Hotel, 3rd Floor, Cornell
11:30 AM - *HH5.01
Vitrimers Meet Supramolecular Chemistry: Towards High Performance Functional Polymer Materials and Composites
Ludwik Leibler 1
1ESPCI Paris Tech Paris FranceShow Abstract
Solid at low temperatures and malleable when heated yet insoluble whatever the temperature, vitrimers constitute the third class of polymers along with thermoplastics and thermosets (elastomers). Vitrimers are made of polymer networks that are able to change their topology without changing the total number of bonds through thermo-activated catalytically controlled exchange reactions. When equipped with specifically associating or crystallizable moieties vitrimers can exhibit very reach mesoscopic and macroscopic organizations. We will discuss how these novel functional organic and composite materials with unprecedented performances can be sythesized from industrially available monomers and molecules. Since vitrimers can be shaped, assembled, repaired and recycled just like the glass, besides opening intriguing perspectives in both physics and chemistry, functional vitrimer systems should rapidly find applications in automotive, electronics, airplane, and coatings industries.
12:00 PM - HH5.02
Dynamic Supramolecular Material Fueled by a Chemical Reaction
Wouter Hendriksen 1 2 Job Boekhoven 3 Ger Koper 1 2 Rienk Eelkema 1 2 Jan Esch 1 2
1TU Delft Delft Netherlands2Advanced Soft Matter Delft Netherlands3Institute for BioNanotechnology in Medicine Chicago United StatesShow Abstract
Dissipative self-assembly of natural macromolecular building blocks is at the basis of many essential processes in living organisms, including cellular transport, cell dynamics, and morphogenesis. Driven by the conversion of chemical fuels, structures such as microtubules are sustained far from thermodynamic equilibrium, leading to localized, transient assembly of architectures with adjustable dynamics1. Characteristically, these active materials are maintained only for as long as useful energy is available to the system.
Recently developed synthetic materials that are obtained under kinetically-controlled conditions, exhibit a rich structural diversity and new functionality compared to equilibrium-processed materials. Nevertheless, they still reside at (local) thermodynamic minimum and lack the dynamic character of natural out-of-equilibrium materials.
Here, we explore the potential of synthetic active materials using the dissipative self-assembly of a small molecule gelator system fueled by a chemical reaction2. General design principles are used to develop our current example, which contains the (de)activation of the small molecule gelator dibenzoyl cystine, DBC, and operates in water at room temperature, on timescales of hours to days. The interesting dynamic properties of this system are investigated using several techniques, such as rheology and confocal microscopy, and are related to the reaction kinetics. We observe a fuel dependent self-healing behavior of the gels and macroscopic time dependent gel stiffness. On the microscopic scale we observe dynamic instability of individual fibers, which is dependent on the reaction conditions3.
Our work shows a new approach to materials that are formed far from equilibrium, with properties that are related to the chemical reaction conditions. The observed fuel dependent self-healing behavior and dynamic instability of the gel fibers are key developments towards more complex synthetic active materials.
1) F. J. Ndlec, T. Surrey, A. C. Maggs, S. Leibler, Nature 389, 305-8 (1997).
2) J. Boekhoven, A.M. Brizard, K. Kowlgi, G.J.M. Koper, R. Eelkema, J.H. van Esch. Angew Chem Int Ed (2010), 49: 4825-4828. doi:10.1002/anie.201001511.
3) Manuscript in preparation
12:15 PM - HH5.03
End-Associative Polymers in Organic Liquids: From Mist Control to Ultra-Soft Gels
Boyu Li 1 Julia A. Kornfield 1
1California Institute of Technology Pasadena United StatesShow Abstract
Associative telechelic polymers have been widely used as rheological modifiers in aqueous and organic solvents, e.g. HEURs and telechelic ionomers. In the course of studies of telechelic polymers with end-groups that associate by hydrogen bonding, we discovered a surprising (to us) rheological regime. In contrast to the usual Arrhenius temperature dependence, we found a window of concentration (temperature) in which the temperature dependence of the relaxation time was anti-Arrhenius. The effect was observed for a 45 kg/mol (Mw) telechelic (carboxylate-ended) polycyclooctadiene (PCOD) near its overlap concentration.
Semidilute, unentangled solutions of 45 kg/mol carboxylate-ended PCOD (0.6 wt% to 2 wt%) in phenyloctane were interrogated using steady and dynamic shear at temperatures ranging from 60 oC to 0 oC. The relaxation time (tau;) and high frequency modulus (Ginfin;) are obtained by fitting the dynamic moduli with a single Maxwell mode. A critical temperature (Tc) is found for each concentration at which the temperature dependence of relaxation time switches from anti-Arrhenius at higher temperatures to Arrhenius at lower temperatures. Above Tc, the relaxation time (on the scale of ms) increases with temperature—an anti-Arrhenius trend, and the high frequency modulus decreases by more than one order of magnitude. In contrast, below Tc the relaxation time becomes much longer (up to 10-1 s) as temperature is reduced (the familiar Arrhenius trend), and the high frequency modulus is roughly constant (variations of around 10%). The shear rate dependence of the viscosity also shows the existence of a critical temperature: the viscosity is independent of shear rate above Tc. We interpret this as evidence that micelles formed by the telechelics are not extensively connected. In contrast, below Tc significant shear thickening is observed, followed by shear thinning, characteristic of formation of an interconnected network. More significantly, the critical temperature for the change in the shear-rate dependence of the viscosity coincides with Tc for the appearance of anti-Arrhenius to Arrhenius temperature dependence.
We postulate that this switch is related to the topology of association (from a micelle-packing mediated solution to an interconnected network). The anti-Arrhenius relaxation time is related to the time it takes for an associative end to escape from the micelle core. As the temperature drops, the conformation of micelles changes: there are fewer loops and more bridges formed between micelles (which we plan to test using scattering experiments), resulting in a shorter relaxation time and a higher modulus. When bridges predominate, Arrhenius behavior results due to the activation energy for hydrogen-bond exchange of network junctions.
12:45 PM - HH5.05
Photopatterning of a Supramolecular Hydrogel Using a Light Triggered Catalyst
Chandan Maity 1 Jan H van Esch 1 Rienk Eelkema 1 Wouter Hendriksen 1
1Delft University of Technology Delft NetherlandsShow Abstract
The formation of supramolecular hydrogels and their resulting mechanical properties can be controlled through in situ catalysis of the gelator molecule formation from two non-assembling building blocks. Control over the spatial distribution of the hydrogel is achieved using a photoswitchable catalyst during in situ gelator formation. The photochromic compound, upon irradiation, temporarily lowers the pH of a solution via proton photo-dissociation, catalyzing the hydrazone gelator formation. Spatial control over gel formation is accomplished by local catalyst activation using a simple photomask, leading to the formation of patterned hydrogels.
Alfredo Alexander-Katz, Massachusetts Institute of Technology
Matthias Schneider, Boston University
Ting Xu, University of California, Berkeley
HH8: Poster Session: Supramolecular Assembly
Thursday PM, April 09, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - HH8.02
Thermo-Responsive Multicolor Luminescence Switching Hydrogel with LCST Behavior
Junjie Cui 1 Dong Ryeol Whang 1 Soo Young Park 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Herein we report on a novel thermo-responsive multicolor luminescence switching hydrogel system comprising a small molecular fluorescent gelator, namely EO7-Py-DCS and poly(acrylic acid) (PAAc) as a polymeric binder. EO7-Py-DCS/PAAc mixture (1:20 wt:wt) in deionized water shows lower critical solution temperature (LCST) type sol-to-gel transition at 60 °C, with concomitant luminescence color changes from red (lambda;PL= 608 nm, sol state) to orange (lambda;PL= 582 nm, gel 1 state). Moreover, further heating of the orange gel gradually changes the luminescence color to green (lambda;PL=514 nm, gel 2 state). Systematic photophysical and structural studies have shown that the unique LCST and thermochromic behaviors of the mixture originate from a thermodynamically controlled competition between self-assembly and hydrogen bonding as follows: i) EO7-Py-DCS self-assembles into micellar structures at low temperature, thus prevents pyridyl groups of EO7-Py-DCS from forming hydrogen bond with the carboxyl groups of PAAc and shows excimeric red emission, ii) upon heating, the ethylene oxide chains become dehydrated and form a hydrogel through physical crosslinking between the pyridine moiety and carboxylic acid group, and iii) upon further heating, nanostructures of EO7-Py-DCS gradually disintegrate into monomers and the luminescence color changes to monomeric green emission.
9:00 AM - HH8.03
Supramolecular Hydrogels via Cucurbituril Ternary Complexation for Delivery Applications
Rebecca Ann Forster 1
1University of Cambridge Cambridge United KingdomShow Abstract
A drug candidate will often be chemically modified to overcome high toxicity, other biological activities, insolubility, or absorption and metabolism difficulties before it may be used in the treatment of disease. These modifications can reduce the overall potency of the drug for the initial condition, but are essential for ensuring the drug meets its target site within the body. The preparation of crosslinked polymer networks formed via cucurbituril ternary complexation that exhibit both shear-thinning and self-healing properties have been recently reported1-2. These materials are potential candidates for the injectable delivery and sustained release of drugs and proteins. Cucurbituril is a member of the larger cucurbit[n]uril (CB[n]; n = 5-8, 10) family. These macrocyclic host molecules closely resemble barrels in shape. CB is particularly interesting for its ability to bind two guests simultaneously. When these two guests are covalently attached to distinct polymer chains, assembly of the ternary complex leads to the formation of crosslinks and an insoluble polymer network. The release of cargo encapsulated within such polymer networks is typically controlled through adjustments in polymer concentration, nature of the polymeric backbone, and the crosslinking density. The properties of hydrogels prepared via CB ternary complexation can be further tuned by choice of guest3. The use of non-toxic guests and guests responsive to UV light has been investigated. Furthermore, hydrogels that are sensitive to environmental changes have found utility in the site-specific and pulsatile delivery of drugs. The incorporation of iron oxide nanoparticles (Fe3O4) into these hydrogels to yield an injectable material that can be heated to undergo a gel-to-sol transition on application of an alternating magnetic field for triggered drug release will also be discussed.
 Appel, E.A.; Loh, X. J.; Jones, S.T.; Dreiss, C.A.; Scherman, O.A. Biomaterials (2012) 33, 4646
 Rowland, M.J.; Appel, E.A.; Coultson, R.J.; Scherman, O.A. Journal of Materials Chemistry B (2013) 1, 2904
 Appel, E.A.; Forster, R.A.; Rowland, M.J.; Scherman, O.A.; Biomaterials (2014) 35, 9897
9:00 AM - HH8.04
Tricarb: Triangular Carbazolo Triazolophane Macrocycles Catch Large Anions with CH H-Bonds and Stack into Tubes on Graphite
Brandon E Hirsch 1 Semin Lee 1 Yun Liu 1 Steven L Tait 1 Amar H Flood 1
1Indiana University Bloomington United StatesShow Abstract
The rational design and synthesis of novel macrocycles can lead to the discovery of new materials. Here we present pioneering work on the development of a carbazole-triazole based shape-persistent macrocycles Tricarb (TC) that are capable of capturing large anions such as iodide with high binding affinities when adsorbed on the surface of HOPG as revealed by scanning tunnelling microscopy. In addition the macrocycle displays remarkable self-association properties that arise from alternating dipoles around the backbone of the TC molecules. This self-association was investigated at the interface of a solution and surface to reveal cofacial stacking of the TC molecules into tubular assemblies away from a graphite surface in two different packing phases, “chickenwire” at high density and “flower” at low density. These unprecedented host-guest complexation capabilities and self-association properties may lead to the development of new charge transport materials and possibly the realization of synthetic ion channels.
9:00 AM - HH8.05
2D Supramolecular Cooperative Assembly Monolayers
Xisen Hou 1 Chenfeng Ke 1 J Fraser Stoddart 1
1Northwestern University Evanston United StatesShow Abstract
Since the discovery of graphene #8210; a naturally occuring two-dimensional (2D) material #8210; materials possessing periodic 2D structures have attracted much attention on account of their potential applications in chemistry, materials science and electronics. From a synthetic perspective, these 2D materials are perfect polymers that extend into two dimensions by dint of their covalent bonds. It is, however, challenging to make artificial analogues of graphene using state-of-art polymer synthetic strategies. This situation is a consequence of the fact that in conventional polymer synthesis, covalent bond formation is irreversible: even one connectivity error can lead to amplified structural irregularities in the final product. In the natural world, the 2D layers of graphite are formed by a process that occurs under thermodynamic control, albeit on geological timescales. Applying the same concept, by introducing reversible chemical bond formation1, chemists can make a series of polymer materials that are extended in two dimensions, namely covalent organic frameworks2 (COFs). Exfoliating COFs into monolayers is difficult because the dynamic bonds are usually vulnerable to their environments.
In contrast to covalent bond formation, noncovalent bonding interactions possess intrinsically reversibility as a result of the very low kinetic barrier between bond breaking and bond making. Although noncovalent bonding interactions are ideal for the construction of molecular assemblies in 2D under thermodynamic control, the materials obtained are even more fragile when compared to COFs. Furthermore, the superstructure of molecular assemblies are dynamic in solution. In this investigation, we have introduced a new concept, namely cooperative assembly, to construct two-dimensional materials benefiting from both covalent bonds and noncovalent bonding interactions. In the initially investigations, we synthesized a one-dimensional polymer by the cooperative capture3 method incorporating a diazaperopyrenium (DAPP) moiety in each repeating unit. In solution, the DAPP moieties from different polymer chains cross-stack perpendicularly, resulting in a two-dimensional polymer in the form of monolayers which can be observed by TEM.
Rowan, S. J.; Cantrill, S. J.; Cousins, G. R. L.; Sanders, J. K. M.; Stoddart, J. F., Angew. Chem. Int. Ed. 2002,41, 898minus;952.
(a) Cote, A. P.; Benin, A. I.; Ockwig, N. W.; O'Keeffe, M.; Matzger, A. J.; Yaghi, O. M., Science 2005,310, 1166minus;1170.
(a) Ke, C.; Strutt, N. L.; Li, H.; Hou, X.; Hartlieb, K. J.; McGonigal, P. R.; Ma, Z.; Iehl, J.; Stern, C. L.; Cheng, C.; Zhu, Z.; Vermeulen, N. A.; Meade, T. J.; Botros, Y. Y.; Stoddart, J. F., J. Am. Chem. Soc. 2013,135, 17019minus;17030; (b) Ke, C.; Smaldone, R. A.; Kikuchi, T.; Li, H.; Davis, A. P.; Stoddart, J. F., Angew. Chem. Int. Ed. 2013,52, 381minus;387.
9:00 AM - HH8.06
Control Large Nanoparticle Assemblies in Thin Films
Jingyu Huang 1 Ting Xu 1
1University of California Berkeley Berkeley United StatesShow Abstract
Nanocomposites can generate new properties beyond those offered by organic and inorganic building blocks to meet the demands in functional materials. The collective properties of nanocomposite materials depend on both the nature of individual building block and their spatial arrangements. With the recent development, colloidal synthesis and surface modification methods provide inorganic nanoparticles (NPs) with various sizes, shapes, compositions and properties in a facile manner. Block copolymer-based supramolecules further provide more versatile routes to control spatial arrangement of the nanoparticles over multiple length scales. Nanoparticle size is a critical parameter determining the optical and electronic properties. However, most of studies to date focused on nanoparticle smaller than 10 nm in size. Here, our recent studies showed that the assembly of nanoparticles with size larger than 10 nm can be achieved in the supramolecular nanocomposite thin films by finely tuning the ligand-polymer interactions and the sample treatment conditions. Both the overall morphology of the nanoparticle assemblies and inter-particle distances can be readily tailored. These new results opened a viable approach to construct functional materials using nanoparticles with different quantum confinement effects.
9:00 AM - HH8.07
Gelation Behavior of Silk Fibroin Dissolved in Formic Acid by Addition of Nitrate Salts
Dong Su Im 1 Won Ho Park 1 MinHee Kim 1
1Chungnam National University Daejeon Korea (the Republic of)Show Abstract
Polymer organogel which three-dimensional network structure cross-linked by physical or chemical methods has the property to swell by absorbing a large amount of the organic solvent. As representative fibrous protein, silk can be obtained silkworm and spider. Because of excellent physical properties, biodegradability, biocompatibility, it has been used as sutures. Silk has been actively studied in the field of tissue engineering. Silk fibroin which account for majority of glycine, alanine, serin can be processed into various form, but when it process into gel form has too much time. In this study, we analyzed the gelation behavior characteristics of the addition of various concentrations of sodium nitrate (NaNO3) was dissolved in formic acid.
Silk fibroin obtained by refing Bombyx mori silk in sodium hydrogen carbonate solution for 30 minutes dissolved in solvent mixed of calcium chloride : ethanol : water = 1: 2: 8 (molar ratio) for 4 hours at 80 #8451;, it was prepared a silk fibroin aqueous solution by dialysis in distilled water for 3 days. Regenerative silk fibroin sponge was prepared through lyophilization of silk fibroin aqueous solution for three days. Gelation behavior of silk fibroin was observed by the addition of 1-10 wt% of sodium nitrate in 5 wt% in the formic acid which was dissolved silk fibroin sponge. Generated gas by adding sodium nitrate in formic acid was confirmed by gas chromatography (GC). Prepared gel dried by exchange water for eliminate formic acid and change of amino acid and its contents was observed by amino acid analysis (AAA). Besides, we analyzed the physical and chemical properties of silk fibroin gel by a variety of analyzes.
Amino acid analysis results of before and after the gelation, tyrosine content decreased, and observed new peak in the vicinity of the retention time 21.880 was identified 3-nitrotyrosine by the spike test. Through this result, it was found that tyrosine conversion to 3-nitrotyrosine occur by adding sodium nitrate into silk fibroin solution and tyrosine occur to silk fibroin gelation as a side reaction.
9:00 AM - HH8.08
Rational Molecular Design of Fluorescent and Photo-Responsive Polymer Gel
Hyeong-Ju Kim 1 Dong Ryeol Whang 1 Soo Young Park 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Stimuli-responsive organogels have received extensive attention for smart materials with their potential applications for delivery systems, sensors, actuators, chemical valves and switches, and artificial muscles. Especially, photo-responsive fluorescent organogels are of great interest since their emission features can be reversibly controlled by light. Most photo-responsive gels consist of low molecular weight photoswitching gelators, because of their high conversion quantum efficiencies and drastic optical properties between two photoswitchable states. However, mechanical and thermal stabilities of these materials systems are relatively low compared to those of polymeric system due to a non-covalent interactions of the small molecules. One of the simple and effective strategies to enhance the mechanical and thermal properties of organogel system is simply blending the low molecular weight materials with polymeric binders.
In these contexts, herein we report on a unique and novel strategy for photo-responsive and fluorescent switching supramolecular polymeric gel by hybridizing a photochromic low molecular weight crosslinker and a polymeric binder. The gel system comprises a photoisomerizable crosslinker, namely 4,4prime;-di(4-pyridyl)cyanostilbene (Py-CN-MBE) and poly(acrylic acid) (PAA) as a polymeric binder. Py-CN-MBE/PAA mixture in ethanol (5mg/30mg in 1mL) forms supramolecular gel through hydrogen bonding interactions between the pyridyl groups of Py-CN-MBE and the carboxyl groups of PAA. Aggregation-induced enhanced emission (AIEE) character of Py-CN-MBE enables a very high quantum yield of the gel (Phi;PL = 0.68) with green emission color (lambda;max = 540 nm). The gel collapses to a blue-emitting (lambda;max = 500 nm and Phi;PL = 0.12) sol upon irradiation of 365 nm light due to photoisomerization of Py-CN-MBE and concomitant breaking of the hydrogen bonding. This study highlights that a photo-responsive and fluorescent switching gel was demonstrated with an aid of reactive polymeric binder, while maintaining efficient photochromic behavior and high fluorescence quantum yields of the small molecular weight crosslinker by means of supramolecular approach.
 J. Eastoe, M. Sanchez-Dominguez, P. Wyatt, R. K. Heenan, Chem. Commun., 2004, 2608 - 2609; J. W. Chung, S.-J. Yoon, S.-J. Lim, B.-K. An, S. Y. Park, Angew. Chem. Int. Ed.,2009, 48, 7030 -7034.
 D. J. Cornwell, B. O. Okesola, D. K. Smith, Soft Matter, 2013, 9, 8730-8736.
9:00 AM - HH8.09
Nitrogen-Physisorption as a Tool to Characterize Temperature Dependent Van der Waalrsquo;s Spacing in a Non-Covalent Supramolecular System
Praveen Kolla 1 Rob Cook 2 Srinagesh Potluri 3 Alevtina Smirnova 1
1South Dakota School of Mines and Technology Rapid City United States2Zyvex Technologies Rapid City United States3Zyvex Technologies Columbus United StatesShow Abstract
Nitrogen-physisorption methods were widely used to study the quantitative and qualitative textural characteristics of porous materials. The volume of the gas adsorbed on a solid-surface is directly proportional to the partial pressure of the adsorbate gas and inversely proportional to the temperature, at the solid-gas interface. The conventional BET system measures the volume of nitrogen adsorption-desorption isotherms as a function of partial pressure of adsorbate gas at a constant liquid-nitrogen temperature of 77K. On the other hand, single-point Specific Surface Area (SSA) and Total Pore Volume (TPV) can be also measured by determining the volume of gas adsorbed during adsorption-cycle (by placing the porous material at liquid nitrogen temperature of 77K) and during desorption-cycle (by placing material at room temperature), using gases having constant nitrogen partial pressures of 0.30 and 0.98, respectively. The objective of the current study is to employ these traditional nitrogen-physisorption techniques in order to understand the temperature dependent Van der Waal&’s Spacing in a Non-covalent Supramolecular System. Development of these analytical tools to understand the Van der Waal&’s interaction in the supramolecular system would be a great advantage for the applications such as electrochemical storage systems and polymer based-composites.
The SSA and TPV measurements of a non-covalent supramolecular system, i.e. a monomer and CNT system were compared with that of neat-CNT samples. Where the volumes of the gas were measured during adsorption-desorption cycles by recording Thermal Conductivity Detector (TCD) signals as a function of time. The SSA and TPV values of the supramolecular system were decreased compared to neat-CNT samples due to presence of monomer. However, the TCD profiles of the supramolecular system and neat CNT samples show significant anomalies in their adsorption-desorption cycles. For example, the supramolecular system shows up to ~10% difference in SSA between adsorption-desorption cycles whereas neat CNT have up to ~1% SSA difference between adsorption-desorption cycles, which is typical for porous materials. Additionally, a higher area under the TCD profile of the desorption cycle in the supramolecular system followed by adsorption at room temperature can be used to quantitatively determine the non-covalent Van der Waal&’s interaction of monomers with CNTs. Further studies such as Temperature Programmed Physisorption (TPP) from room temperature to 150oC and nitrogen isotherms at liquid-nitrogen temperature of 77K and dry ice (bath containing a mixture of ethylene glycol and ethanol) temperatures of 200K were carried out. The TPP profiles and Pore-Size distribution results of the supramolecular system compared to the neat-CNTs will be discussed as an evidence to characterize temperature dependent Van der Waal&’s spacing in the non-covalent Supramolecular System.
9:00 AM - HH8.10
Layer-by-Layer (LbL) Films of Functionalized Reduced Graphene Oxide Nanosheets for Glucose Detection
Daniela Branco Tavares Mascagni 1 2 Antonio Riul 3 Nilson Cristino da Cruz 1 Marystela Ferreira 2
1Paulista State University - UNESP Sorocaba Brazil2Federal University of Satilde;o Carlos - UFSCar Sorocaba Brazil3State University of Campinas - Unicamp Sorocaba BrazilShow Abstract
In this work, reduced graphene oxide was synthesized by Hummer&’s method and functionalized with poly (diallyldimethylammonium chloride) (PDDA) and poly (styrene sulfonate) (PSS) to introduce, respectively, positive and negative charges on the surface of the graphene nanosheets, enabling also stable aqueous dispersions for the production of supramolecular architectures using the layer-by-layer technique (LbL). LbL films permit the immobilization of glucose oxidase on graphene nanoplatelets, preserving the biocatalytic activity of the enzyme. Cyclic voltammetry results showed that the architecture of the films deposited on Indium Tin Oxide electrode (ITO) preserve the native structure of the enzyme as well as an effective transfer of electrons from the redox reactions. A quasi-reversible process was also revealed, confirmed by the linear relationship between different scan rates. Results show a detection limit of 46 mu;mol.L-1, 7.6 mu;A.cm-2.mmol-1.L sensitivity and good linearity with the addition of glucose in the range of 0.2 to 1.2 mmol.L-1. Amperometric results shown operating potential of -0.3 V and linear response due to the addition of glucose between 0.28 and 1.37 mmol.L-1, with a detection limit of 5.6 mu;mol.L-1 and sensitivity of 0.34 mu;A.cm-2mmol-1.L. Additionally, the effectiveness of the synthesis of graphene nanosheets and enzyme immobilization in nanostructured LbL films was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-Vis and infrared spectroscopy (FTIR).
Acknowledgment: Capes, CNPq, Fapesp (2012/16158-0)
9:00 AM - HH8.11
Dynamics of DMPC Phospholipid in Unilamellar Vesicles: Effect of Addition of Melittin and Cholesterol
Veerendra Kumar Sharma 1 D. B. Anunciado 1 E. Mamontov 2 H. O'Neill 1 V. Urban 1
1Oak Ridge National Laboratory Oak Ridge United States2Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
Melittin is a hemolytic peptide known for its strong interaction with the membrane, making it a popular target for studying peptide-lipid interaction. It has been shown that melittin binds to the head group of phospholipid and changes its conformation from random coil to alpha helical. Cholesterol is an essential component of cell membranes which controls the fluidity and the packing state of the bilayer. Therefore, it is of interest to investigate dynamics of lipids based vesicles in the presence of cholesterol and membrane-active peptides e.g. melittin. Here we report a quasielastic neutron scattering (QENS) study on the effect of melittin and cholesterol on the dynamical behavior of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) phospholipid unilamellar vesicles (ULV), a mimic of cell membrane. Elastic scans have been carried out on DMPC based ULV with cholesterol (4:1 mol), melittin (500:1 mol) and DMPC:cholesterol:melittin (500:125:1 mol) in the temperature range 260-310K. We have observed that the addition of cholesterol or melittin inhibits the appearance of a step fall in the elastic intensity at 297 K, which is observed in case of pure DMPC vesicles. This step fall in elastic intensity corresponds to solid gel to fluid phase transition. This is an indication that the added molecules affect the solid gel to fluid phase transition of DMPC vesicle. Differential scanning calorimetric measurements show that the addition of cholesterol broadens the transition peak, whereas melittin shifts the transition to higher temperatures. To investigate dynamical motions in details, QENS experiments have been carried out on DMPC ULV in presence of cholesterol and melittin at two different temperatures below and above the phase transition, 280 and 310 K. Detailed data analysis clearly shows the presence of two distinct motions: lateral diffusion, or whole lipid molecule motion, and the faster internal motion of the DMPC monomer. It is found that in solid gel phase (at 280 K), addition of cholesterol did not affect the dynamics of lipids significantly. However, in the fluid phase (at 310 K), both the motions, i.e., lateral as well as internal, are found to be affected. The addition of cholesterol in the fluid phase enhances the stability of the lipid vesicles since cholesterol acts as a stiffening agent which hinders both lateral as well as internal motions. On the other hand, melittin (0.2 mol%) affects dynamics in a significantly different way, depending on the phase of lipid bilayers. In the solid gel phase, it acts as a plasticizer enhancing the dynamics of lipid molecules. However, in the fluid phase melittin acts oppositely and slows down the dynamics of the lipid molecules. Interestingly, the addition of melittin to the vesicles containing cholesterol does not affect much the lipid dynamics, and found to be very similar to DMPC with cholesterol. These observations are consistent with the obtained MSD from elastic intensity scans.
9:00 AM - HH8.12
MOF-177/Graphene Composite as a Selective Sensor for Nitro Aromatic Compounds
Venkata Neti 1
1University of Utah Salt Lake City United StatesShow Abstract
A zinc-based metal-organic framework, MOF-177, was synthesized on the surface of benzoic acid functionalized reduced graphene oxide (BFG). Large amounts of BFG (30wt %) improved the stability of the MOF on the graphene surface, decreased the porosity of the composite, and resulted in 1mm long and 50µm wide microrods of MOF-177/BFG composites which act as a selective sensor for trinitrophenol compared to trinitrotoluene.
9:00 AM - HH8.13
Influence of Three-Dimensional Nanoparticle Branching on the Youngrsquo;s Modulus of Polymer Nanocomposites
Shilpa N Raja 1 Aditya Limaye 1 Andrew Olson 1 Kari Thorkelsson 1 Andrew Luong 1 Liwei Lin 1 Robert O. Ritchie 2 Ting Xu 2 A. Paul Alivisatos 3
1UC Berkeley/LBNL Berkeley United States2Univ of California-Berkeley Berkeley United States3Univ of California-Berkeley Berkeley United StatesShow Abstract
With the advent of the ability to prepare nanoparticles with controlled size and shape, there has been renewed interest in the study of the mechanical properties of polymer-nanoparticle composites. Due to their high filler-polymer interfacial area, polymer nanocomposites have the ability to achieve mechanical propery improvements at very low weight percents. Despite the large number of theoretical studies on the effect of nanoparticle shape on Young&’s modulus, the effect of three-dimensional nanoparticle branching on the Young&’s modulus of supramolecular polymer nanocomposites has not been studied experimentally. Here, we examine the supramolecular nanocomposite Young&’s modulus for three different nanoparticle morphologies, spheres, rods, and branched tetrapods, in a common structural elastomer, poly(styrene-block-ethylene-butylene-block-styrene) (SEBS). Nanoparticles are incorporated into polymers using electrospinning; fibers range from 2-10 um thick. Nanoparticles and polymers interact via like-like interaction between the hydrophobic nanoparticle surface ligands and the hydrophobic domains of SEBS. The results indicate that the branched nanoparticles in this study, nanoscale tetrapod Quantum Dots (tQDs), impart the best improvements, enhancing the Young&’s modulus of SEBS by 2.5 times at 20% loading of tQDs by weight, 1.5 times more than nanorods (NRs). Simulations using a 2D lattice spring model (LSM) suggest that the enhanced Young&’s modulus in tQD-nanocomposites may result from an orientational optimization of both nano-filler and interfacial bonds due to its isotropic shape. Importantly, our results suggest that not only is the orientation of the nanoparticle filler important as is traditionally thought, but that the orientation of strong X-type bonds at the interface between organic and inorganic can be equally important in optimization of composite mechanical properties. The nanoscale branched tQD may represent such an orientational optimization of interface and filler bonds. Furthermore, in this study, we examine the validity of these simple phenomenological Lattice Spring Models (LSMs) to predict the mechanical properties of such composites in the small displacement elastic limit. Reasonable qualitative agreement between the results from the LSMs and from experiments for all three nanoparticle shapes, through accounting only for a few key physical assumptions, suggests these models are advantageous tools for nanocomposite design and for developing a mechanistic understanding of nanocomposite function.
9:00 AM - HH8.14
NMR Methodologies for the Detection and Quantification of Nano-Structural Defects in Model Silicone Networks
Jennifer Nicole Rodriguez 1 James P Lewicki 1 Stephen J. Harley 1 Thomas S, Wilson 1 Ward Small 1 Robert S Maxwell 1
1Lawrence Livermore National Laboratory Livermore United StatesShow Abstract
Polysiloxanes are the most utilized non-carbon backboned polymeric material today and find use in a range of academic, commercial and industrial applications; including medical devices, chemically inert lubricants, thermally resistant elastomers and flexible electronics. However, polysiloxane elastomers almost without exception, require chemical & physical modification (e.g. multi-modal chain lengths, variable crosslink densities, modified chain ends, and the addition of fillers) in order to form useful materials. The resulting structure of such network elastomers is consequently, complex, hierarchical and often ill-defined. And although such polysiloxane elastomers are widely used, characterization of these materials network structure - in relation to service lifetime, performance and degradation, is limited. Furthermore, the chemical origins of the aging and degradation processes (e.g. chain scission, x-linking & rearrangement) occur at molar levels which challenge the detection limits of many polymer spectroscopies. Here we present and discuss a direct and sensitive means of detecting and quantifying network defects and other trace chemical signatures of degradation in siloxane based materials by means of solution state Nuclear Magnetic Resonance (NMR). We have designed model siloxane based networks with controlled levels of ‘defect&’ sites, meant to simulate the aging process. At the defect sites, these model networks were subsequently tagged with reactive organo-fluorines which can be readily detected and quantified via 19F NMR. We also discuss the application of this method as a tool to measure the degradation of non-model engineering polysiloxane materials.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
9:00 AM - HH8.15
Photoresponsive Fe(III)-Polysaccharide Hydrogels for Light-Controlled Drug Delivery
Christopher T. Sosnofsky 1 Giuseppe E. Giammanco 1 Alexis D. Ostrowski 1
1Bowling Green State University Bowling Green United StatesShow Abstract
We report the formation of hydrogel materials from Fe3+ and naturally- occurring plant polysaccharides alginate and pectate. We formed Fe(III)-polysaccharide hydrogel beads that hold epinephrine and other drug models, inside the polysaccharide network. The beads were stable in distilled water and certain buffers at pH 7 in the dark for over 6 months. Upon irradiation of the hydrogels, Fe3+ was reduced, which causes a disruption in the crosslinking and resulted in the breaking apart of the hydrogel bead and release of the drug cargo. The stability and reactivity of the beads were tested for both alginate and pectate. Pectate beads were less reactive than alginate after irradiation with visible (405 nm) light. Quantitative comparison of the efficiencies of the photoreduction (QYs) for alginate and pectate solutions indicated that the photoreaction was more efficient in alginate than pectate. This mirrors the photoreactivity of the hydrogel beads. The dramatic difference in QYs from two similar polysaccharides led us to investigate the role of different functional groups on the photoreaction. The polysaccharides were modified by acetylating (Ac) and carboxomethylating (Cx) some hydroxyl groups. The QY was determined and both the Ac and Cx polysaccharides displayed lower QYs compared to the parent polysaccharides. We hypothesize that these different QYs were due to the changes in supramolecular structure and binding of Fe3+ with the polysaccharides. Future work will also focus on tuning of the drug release from the Fe(III)-polysaccharide hydrogels by changing the polysaccharide used to build the hydrogel materials.
9:00 AM - HH8.16
ldquo;Weakrdquo; Interactions Provide Strong Handle on Redirecting Bonding in Self-Assembled Hybrid Metal Organic Chalcogenides
Ryan Swoboda 1 Fei Hua Li 1 James Nathan Hohman 2 Nicolas A Melosh 2
1Stanford University Stanford United States2Stanford University Stanford United StatesShow Abstract
One dimensional metal chalcogenides (MCs) are an emerging materials class with unique electronic, catalytic, mechanical and optical properties. The challenge with chemical synthesis of MCs lies in the construction of systems that can direct chalcogen-metal connectivity and provide a platform for manipulating dimensionality, lattice strain, and band gap. Here, we report a template for the self-assembly of hybrid metal organic chalcogenides by which addition occurs at a catalytic surface pinned at a liquid-liquid interface. The chalcogenide bonding is linked to molecular ligand geometry and van der Waals interactions within the material. We examine hybrid metal organic chalcogenide self-assembly kinetics, and demonstrate that the autocatalytic reaction mechanism constitutes a basis for reliable assembly of a wide range of related material products.
9:00 AM - HH8.17
Self-Assembled Nanoflowers via Polydiacetylene-Based Organic Frameworks (POFs)
Songwen Tan 1 Doo Ho Yang 1 Jin Hyuk Park 1 Jinkyu Roh 1 Seung Hyuk Back 1 Dong June Ahn 2
1Korea University Seoul Korea (the Republic of)2Korea Univ Seoul Korea (the Republic of)Show Abstract
Self-assembling is a widely used process in biochemistry. Assembled structures result from one or more interactions: covalent bond, ionic bond, aromatic π-π stacking and other van der Waals forces. Due to self-assembling, several series of organic frameworks (3D) were designed by our group by using di-amine and di-carboxyl interactions. Interestingly, mainly due to ionic interactions and π-π stacking, these frameworks could be self-assembled to porous sphere flower-like structures, while temperature, concentration, reaction time and process influence the geometrical performance, including size, shape, pore size and surface area. Like common covalent organic frameworks (COFs), polydiacetylene organic frameworks (POFs) are also porous, crystalline and were made entirely from light elements (H, C, N, and O). In addition, we specially studied their sensing property by colorimetric and fluorescent performance. The red-color phase has much stronger fluorescence than blue-color phase upon excitation, enabling new approaches for imaging and sensing. As polymer architectures with high surface area and nano pores, these nanoflowers have higher chemical and biological activities. Furthermore, 2D nanoflower garden chips can be achieved by steric limitation.
HH7: Supramolecular Assembly II
Thursday AM, April 09, 2015
Park Central Hotel, 3rd Floor, Cornell
9:30 AM - *HH7.01
Functional Assemblies and Interfacial Dynamics with Cucurbiturils
Oren A. Scherman 1 Matthew James Rowland 1
1University of Cambridge Cambridge United KingdomShow Abstract
We are interested in the development of controlled polymer architectures, hybrid nanoparticle-soft matter assemblies and the integration of dynamic supramolecular systems at interfaces. Current research projects in the group include the application of macrocyclic host-guest chemistry using cucurbit[n]urils in the development of novel microcapsules, supramolecular hydrogels, drug-delivery systems based on dynamic hydrogels, adhesion between a variety of surfaces, the conservation and restoration of important historical artefacts through the exploitation of supramolecular polymer chemistry and sensing and catalysis using self-assembled nanophotonic systems.
Modification of solution viscosity using multivalent polymers has been accomplished through dynamic cross-linking in water using CB. These hydrogels, with extremely high water content (up to 99.75% water by weight), have also been prepared from renewable cellulose derivatives. Their rapid formation and shear-induced flow properties make these materials perfectly suited for use as injectable hydrogels.
Polymer-inorganic composite materials can be readily prepared based on the CB coupling of multivalent gold nanoparticles (AuNPs) to functional copolymers. When these systems are attached onto gold surfaces intricate control is achieved over the site-selective immobilization of colloids and peptides. This has great scope for the development of optical materials, chemical sensors and biological separations. Additionally, we have developed an innovative new technique for manufacturing 'smart' microcapsules in large quantities using continuous flow in a single step from tiny droplets of water. The major advantage of this manufacturing platform over current methods is that a variety of cargos can be efficiently loaded during the microcapsule formation at room temperature, and the dynamic supramolecular interactions provide control over the porosity of the capsules and the timed release of their contents using stimuli. Our CB[n] based host-guest systems exhibit dynamic self assembly and are capable of responding to stimuli (photochemical, chemical, and thermal) allowing for external control and function to be built into the materials.
 Zhang, J.; Coulston, R.; Jones S.T.; Scherman, O.A.; Abell, C. Science (2012) 335, 690.
 Appel, E.A.; Rauwald, U.; Jones, S.; Zayed, J.M.; Scherman, O.A. J. Am. Chem. Soc. (2010) 132, 14251.
 Appel, E.A.; Loh, X.J.; Jones, S.T.; Dreiss, C.A.; Scherman, O.A. Biomaterials (2012) 33, 4646.
10:00 AM - HH7.02
Supramolecular Polysaccharide Hydrogels through Cucurbituril Host-Guest Chemistry
Matthew James Rowland 1 Colin Watts 1 Oren Scherman 1
1Cambridge University Cambridge United KingdomShow Abstract
Various injectable, biocompatible hydrogels that exhibit rapid thixotropic behaviour through utilisation of the dynamic supramolecular host-guest chemistry of cucurbituril (CB) have been designed and synthesised for application in drug delivery devices.1 Cucurbit[n]urils are macrocyclic oligomers of glycoluril linked by methylene bridges, where n determines the number of glycoluril units present in the given macrocycle and therefore the cavity volume. In aqueous conditions, CB has a cavity large enough to encapsulate two aromatic guests, of which the driving force for such encapsulation is the expulsion of “high-energy” water molecules from the hydrophobic cavity, back into the bulk solution. The fabrication of supramolecular hydrogels has been achieved through the functionalisation of high molecular weight polysaccharides such as hyaluronic acid (HA), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and others, with CB guest moieties, namely derivatives of the aromatic amino acids phenylalanine and tryptophan. These amino acids bind in a 2:1 fashion with CB and, when pendant from polymer chains, the favourable non-covalent interactions of the newly formed homo-ternary complexes operate as dynamic, stimuli-responsive (mechanically, chemically and thermally), physical crosslinks between the polysaccharide chains.2 These physical crosslinks transform the dilute, yet viscous polysaccharide solutions into strong, high water content (~99% water), elastic, shear-thinning, thixotropic hydrogels. The moduli, release profiles and other desirable properties can be tuned by simply regulating CB concentration, polymer choice, polymer concentration and selection of the guest moiety.3 The high degree of physical control inherent of this system, as well as its biocompatibility, renders it an excellent choice of material for implantable or injectable therapeutic delivery vehicles. The design and synthesis of such systems, the rheological properties and the applications will be discussed.
1. Appel E. A. Loh X. J., Jones S. T., Dreiss C.A., Scherman O. A., Biomaterials, 2012, 33, 4646-4652.
2. Rowland M. J., Appel E. A., Coulston R. J., Scherman O. A., J. Mater. Chem. B, 2013, 1, 2904-2910.
3. Appel E. A., Forster R. A., Rowland M. J., Scherman O. A., Biomaterials, 2014, 35, 9897-9903.
10:15 AM - HH7.03
Controlling the Self-Assemble of Octapeptides to beta;-sheet Based Hydrogels by Altering their Alanine/Phenylalanine Sequence
Andrew Mark Smith 1 2 Aline Miller 3 1 Alberto Saiani 2
1University of Manchester Manchester United Kingdom2University of Manchester Manchester United Kingdom3University of Manchester Manchester United KingdomShow Abstract
The use of non-covalent self-assembly to construct materials has become a prominent strategy in material science offering practical routes for the construction of increasingly functional materials. A variety of molecular building blocks can be used for this purpose. One such block that has attracted considerable attention in the last 20 years is de novo designed peptides. One family of self-assembling peptides which has attracted particular interest are the so-called “β-sheet forming peptides”. Through the appropriate design of the primary amino acid sequence, short peptides can be designed that self-assemble into β-sheet rich fibres that above a critical gelation concentration entangle/associate to form very stable hydrogels. These materials are thought to have potential in a variety of applications such as tissue engineering and drug delivery.
A particular design developed by Zhang and co-workers is based on the alternation of hydrophilic and hydrophobic amino acids. (Zhang, SG et al.; Biopolymers, 1994, 34, 663) Recently significant work was reported on the effect changing the hydrophobic residues has on the gelation properties of these peptides. (Mohammed A., et al.; Macromolecular Symposia 2007, 251, 88) (Bowerman, CJ, et al.; Biomacromolecules 2011, 12, 2735) Less attention has been given though to the effect that the primary amino acid sequence has on gelation.
Here we report on recent work we performed on the effect that the primary amino acid sequence has on the self-assembling and gelation properties of a series of octa-peptides where the hydrophobic amino acids are phenylalanine (F x 2) and alanine (A x 2) and the hydrophilic amino acids are lysine (K x 2) and glutamic acid (E x 2). Using these amino acids a series of peptides with identical hydrophobicity but different sequences were designed to explore the stability of the β-sheet configuration and the effect this has on the gelation capability of these peptides.
It was found that the sequence of the hydrophobic amino acids has a dramatic influence on the capability of the peptides to self-assemble to fibrous structures and form hydrogels. This relates to a number of factors, the primary two being the ability of the peptide to adopt alternate secondary structures other than a β-sheet, and the packing of the hydrophobic amino acids against one another in a β-sheet structure. These results show that while the overall hydrophobicity of β-sheet forming peptides is important the arrangement of amino acids is critical for controlling hydrogel formation. This work brings new insight into the design rules of these β-sheet forming peptides.
The authors would like to thank the EPSRC Fellowship (Grant no: EP/K016210/1) for providing financial support to this project.
10:30 AM - HH7.04
Molecular Dynamics Simulations of Stacked DNA Base Surrogates
Amir Mazaheripour 1 Cade Markegard 1 Jonah-Micah D Jocson 1 Anthony Burke 1 Alon Gorodetsky 1 Hung Nguyen 1
1University of California, Irvine Irvine United StatesShow Abstract
Organic nanowires represent idealized model systems for understanding the interactions between organic semiconductor building blocks. We have synthesized nanowires consisting of pi-conjugated DNA-base surrogates covalently attached to a DNA-like backbone and studied the self-assembly properties of these constructs with molecular dynamics simulations. The DNA base surrogates were first parametrized through quantum mechanics calculations to create an atomistic model. Constant-temperature molecular dynamics simulations then provided an improved understanding of the kinetics of stacking between adjacent DNA base surrogates. Replica-exchange simulations in turn yielded the atomic structures of our nanowires at equilibrium. By examining the lowest energy structures obtained from our simulations, we have gained insight into the structure and integrity of our nanowires, which would not be readily available through experimental techniques.
10:45 AM - HH7.05
Molecular Prediction of Porous Organic Molecules
Kim E Jelfs 1
1Imperial College London London United KingdomShow Abstract
The modular assembly of discrete, intrinsically porous organic molecules is an alternative to forming porous materials through extended networks that are chemically bonded in 3-dimensions. These modular materials can have advantages, such as being easily processable, co-crystallisation allowing property tuning and their greater mobility facilitating stimuli-response behaviour, such as “on”/“off” porosity switching. From a computational perspective, it has been shown that crystal structure prediction techniques can rationalise the observed polymorphs and we have used molecular dynamics simulations to explain observed sorbate selectivity.[4,5] More recently, we have been developing an approach towards in silico design of new porous molecular materials with desired structures and properties. This automates the assembly and screening of hypothetical molecules from a library of precursors. The first goal is to predict the conformation of the molecule that will be formed. It is crucial to test whether the molecule will be “shape persistent”, keeping an internal void in the absence of solvent, as we have previously spent months synthesising large molecules that collapse upon desolvation. The second goal is to correctly predict which molecule will form from a pair of precursors - e.g. will a [2+3], [4+6], [6+9] or [8+12] reaction occur? We have demonstrated the successful prediction of an odd-even effect for a series of alkane diamines. Further, we can predict how post-synthetic modification can engineer shape-persistence and acid and base-resistance, as well as using computational predictions to engineer novel shaped molecules and to perform rapid computational screening to predict properties for hypothetical molecules. Here we will present our latest results showing the wider applicability of the method to new chemical systems and the potential for these in silico predictions to help guide laboratory syntheses.
 T. Tozawa, J. T. A. Jones, S. I. Swamy, S. Jiang, A. I. Cooper et al. Nature Materials, 8 973 (2009).
 T. Hasell, S. Y. Chong, K. E. Jelfs, D. J. Adams and A. I. Cooper J. Am. Chem. Soc. 134 588 (2012).
 J. T. A. Jones, T. Hasell, X. Wu, J. Bacsa, K. E. Jelfs, A. I. Cooper et al. Nature 367 474 (2011).
 J. T. A. Jones, D. Holden, T. Mitra, T. Hasell, K. E. Jelfs, A. I. Cooper et al. Angew. Chem. Int. Ed. 50 (3) 749 (2010).
 T. Mitra, K. E. Jelfs, M. Schmidtmannm A. Ahmed, A. I. Cooper et al. Nature Chem. 5 276 (2013).
 K. E. Jelfs, E. G. B. Eden, J. L. Culshaw, S. Shakespeare, A. I. Cooper et al. J. Am. Chem. Soc. 135 9307 (2013).
 M. Liu, M. A. Little, K. E. Jelfs, J. T. A. Jones, M. Schmidtmann, S. Y. Chong, T. Hasell, A. I. Cooper, J. Am. Chem. Soc. 136 (21) 7583 (2014).
11:30 AM - HH7.06
Chiral Templating of Self-Assembling Nanostructures by Circularly Polarized Light
Jihyeon Yeom 2 Bongjun Yeom 1 Henry Chan 3 Kyle Smith 4 Sergio Dominguez-Medina 4 Joong Hwan Bahng 2 Gongpu Zhao 5 Wei-Shun Chang 4 Sung-Jin Chang 6 Andrey Chuvilin 7 Dzmitry Melnikau 7 Andrey Rogach 8 Peijun Zhang 5 Stephan Link 4 Petr Kral 3 Nicholas A. Kotov 1
1Univ of Michigan Ann Arbor United States2University of Michigan Ann Arbor United States3University of Illinois at Chicago Chicago United States4Rice University Houston United States5University of Pittsburgh School of Medicine Pittsburgh United States6Chung-Ang University Seoul Korea (the Republic of)7CIC NanoGUNE Consolider Tolosa Hiribidea Spain8City University of Hong Kong Kowloon Hong KongShow Abstract
Examples of chemical reactions affected by spin angular momenta of circularly polarized photons are rare and display low enantiomeric excess. High optical and chemical activity of nanoparticles (NPs) should facilitate the transfer of spin angular momenta of photons to nanoscale materials. However, such processes are currently unknown. Here we demonstrate that circularly polarized light (CPL) strongly affects self-assembly of racemic CdTe NPs. Illumination of NP dispersions with right- and left-handed CPL is shown to induce the formation of right- and left-handed twisted nanoribbons, respectively. Enatiomeric excess of such reactions was found to be greater than 30% which is ~10x higher than other CPL-induced reactions. In contrast, illumination with linearly polarized light and assembly in the dark led to straight nanoribbons. The mechanism of “templation” of NP assemblies by CPL is associated with selective photoactivation of chiral NPs and clusters followed by their photooxidation. Chiral anisotropy of interactions translates into chirality of the assembled ribbons. Their strong optical activity is confirmed by ensemble measurements, single ribbon CD spectroscopy, finite element modeling of the chiroptical properties based on Maxwell equations, and atomistic molecular dynamic simulations. The ability of NPs to retain polarization information, or the “imprint” of incident photons opens new pathways for the synthesis of chiral photonic materials and allows for better understanding of the origins of biomolecular homochirality.
11:45 AM - HH7.07
Electrostatic Self-Assembly as Tool for Solar Energy Conversion?
Franziska Groehn 1
1University Erlangen Erlangen GermanyShow Abstract
With regard to the world's decreasing energy resources, developing strategies to exploit solar energy become more and more important. One approach is to take advantage of photocatalysis. Inspired by natural systems such as assemblies performing photosynthesis, it is highly promising to self-assemble synthetic functional species to form more effective or tailored supramolecular units. In this contribution, a new type of photocatalytically active self-assembled nanostructures in aqueous solution will be presented: supramolecular nano-objects obtained through self-assembly of macroions and multivalent organic or inorganic counterions.
Polyelectrolyte-porphyrin nanoscale assemblies exhibit up to 10-fold higher photocatalytic activity than the corresponding porphyrins without polymeric template. Other self-assembled catalysts based on polyelectrolytes can exhibit expressed selectivity in a photocatalytic model reaction or even allow catalytic reactions in solution that are not possible with the building blocks only. Further, current results on combining different functional units at the polyelectrolyte template represent a next step towards more complex supramolecular structures for solar energy conversion.
12:00 PM - HH7.08
Dipping, Spray and Dynamic Layer-by-Layer (LbL) Films of Graphene Nanoplatelets
Waldomiro Luiz Rios de Mello 2 5 Celina Massumi Miyazaki 3 Elidiane C. Rangel 4 Nilson C. Cruz 4 Guilherme Fernandes Nielsen 6 Maria Helena de Oliveira Piazetta 7 Angelo L. Gobbi 7 Antonio Riul Jr 1
1UNICAMP Campinas Brazil2UFSCar Sorocaba Brazil3UFSCar Sorocaba Brazil4UNESP Sorocaba Brazil5CNEN/IPEN Satilde;o Paulo Brazil6CTM Sorocaba Brazil7CNPEM Campinas BrazilShow Abstract
The aim here was check how different ways of nanostructuring thin films impact graphene nanoplatelets multilayer formation, which certainly will affect forthcoming developments and applications. Reduced graphene oxide nanoplatelets were produced using the Hummer&’s method, further reduced with poly(styrene sulfonate) to yield negatively charged stable colloidal suspensions (GPSS). The layer-by-layer technique (LbL) is a self-asserting bottom-up procedure for multilayer formation on free surfaces and in confined geometries (inside a microchannel, for example). Supramolecular nanostructures of GPSS with poly(diallyldimethylammonium chloride) (PDDA) were produced via dipping, spray and dynamic (inside a polydimethylsiloxane (PDMS) microchannel) LbL methodology. A kinetic growth mechanism of both polyelectrolytes was initially checked, with LbL films further characterized by UV-vis, MEV and AFM. Results shown a linear adsorption of the materials in all nanostructures formed, indicative of a good multilayer assembly. LbL films formed by the dynamic process presented higher roughness and material aggregation when compared with the two other methods, which might be handful in microfluidic devices and applications.
12:15 PM - HH7.09
Synthesis and Self-Assembly of Responsive Petpoids
Yulin Chen 1 James J. De Yoreo 1 Chun-Long Chen 1
1Pacific Northwest National Laboratory Richland United StatesShow Abstract
Peptoids, or poly-N-substituted glycines, are an elegant mimetic of peptides. The lack of main-chain hydrogen bonding in peptoids makes them an ideal candidate for understanding the side chain interactions/self-assembly of protein-based materials that are important in the biological system. By manipulating the polarity and functionality of the N-substituted side chains, either nanofibers or nanosheets are readily achievable through the process of self-assembly. The functional group emulating phenylanaline was selected to increase the π-π interaction of the hydrophobic domain in the peptoids. By programming the sequences, we observed that the peptoids self-assembled into different nanostructures. The stability of the peptoid nanomaterials in solvents could be improved by crosslinking of the side chain functional groups. Environmentally responsive peptoid nanomaterials were obtained by introducing reversible chemistry into the sequences. The peptoid nanomaterials were intensively studies by microscopic techniques such as AFM and TEM.
12:30 PM - *HH7.10
Control on Morphology of Ligand Shell in Gold Nanoparticles
Francesco Stellacci 1
1EPFL Lausanne SwitzerlandShow Abstract
When mixtures of ligands are used to coat a gold nanoparitlces it is possible that separation happens between molecules that are dissimilar. This separation can lead to various types of arrangements, ranging from stripes to Janus. In this talk I will review our approaches to characterize this particles and to control such arrangment through external stimuli such as solvent, pH, and temperature. The hyerarchical effect of the arrangement of the molecules on the particles one the assembly of the particles themselves will be dissussed also.