Zhongyang Cheng Auburn University
Qiming Zhang The Pennsylvania State University
Siegfried Bauer Johannes-Kepler University Linz
Debra A. Wrobleski Los Alamos National Laboratory
BB1: New Materials and Characterization
Tuesday PM, December 02, 2008
Grand Ballroom (Sheraton)
9:00 AM - **BB1.1
High Performance Dielectric Elastomers.
Qibing Pei 1 Show Abstract
1 Materials Science and Engineering, UCLA, Los Angeles, California, United States
Several categories of elastomers have been exploited as dielectric elastomers. Acrylic copolymer, silicone, and thermoplastic block copolymers are notable examples exhibiting distinctive electromechanical transduction. We have focused on improving the 3M VHB acrylic films that have already shown the best overall actuation performance when the films are highly prestrained. Interpenetrating polymer networks (IPN) in which the acrylic network is under high tension balanced by compression of an additive network were investigated for further enhanced actuation performance. The IPN films at zero or norminal external prestrain showed up to 300% actuation strain. The calculated values of maximum actuation energy density and electromechanical coupling factor are 3.5 J/g and 93.7%, respectively. Uniaxial stress relaxation analysis showed significant decrease in viscoelastic loss in comparison with the VHB films, the primary component network in the IPN films. Important actuators enabled by the IPN films will also be reported.
9:30 AM - **BB1.2
Nanoscale Interactions in Ferroelectric Polymers.
Stephen Ducharme 1 Show Abstract
1 Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
The properties of ferroelectric thin films and nanostructures are receiving increasing attention due in part to advances in nanoscale fabrication and characterization and in part due to the enormous commercial potential for application of highly integrated ferroelectric devices in a wide range of technologies, such as, nonvolatile memories, micro- and nano-electromechanical systems, ultrasonic transducer arrays, and infrared imaging. The purpose of this presentation is to review some of the more remarkable, and potentially useful, discoveries that have come out of studies of nanoscale interactions in ferroelectric copolymers of vinylidene fluoride with trifluoroethylene. These polymers can be structured into films as thin as a nanometer and nanocrystals as small as 8 nm thick by 90 nm in diameter, while maintaining their essential ferroelectric properties -- bistable polarization, piezoelectric response, and pyroelectric response. Piezoresponse force microscopy, for example, has been used to measure nanoscale polarization with a resolution of 5 nm and to pattern arbitrary polarization patterns with a resolution of 50 nm. This work was supported by the Nebraska Research Initiative, the National Science Foundation, and the Department of Energy.
10:00 AM - BB1.3
Real-Time Study of Surface Layer Formation with Nanomechanical Cantilever Sensors.
Joachim Koeser 1 2 , Martin Bammerlin 1 , Felice Mauro Battiston 1 , Urs Hubler 1 Show Abstract
1 , Concentris GmbH, Basel Switzerland, 2 School of Life Sciences, University of Applied Sciences Northwestern Switzerland, Muttenz Switzerland
Nanomechanical cantilevers are small, microfabricated silicon beams, which transform processes occurring at their surface into a mechanical response with extremely high sensitivity. When studying the formation of surface layers, such as the self-assembly of monolayers or more complex processes like the build-up of layer-by-layer structures or other smart materials, valuable real-time information on the dynamics of these processes can be obtained by employing this unique signal transduction principle. Surface stress occurring within the surface layer can be studied by monitoring the bending of the nanomechanical cantilever (static mode). Simultaneously, measuring changes in the oscillation properties of the cantilever (e.g. resonance frequency, quality factor) provides complementary information about changes in mass load on the cantilever and/or stiffness changes within the layer itself (dynamic mode). Information extracted from both data sets helps to get a better understanding of the layer formation process and provides useful information for the optimization of manufacturing parameters. Additionally, the potential of nanomechanical cantilever sensors as a valuable tool for characterization of surface associated phenomena as well as chemical/biological actuators has been impressively illustrated by examples such as the repeated swelling/collapsing cycles of polymer brushes grown on cantilever sensors or the analysis of forces generated by molecular motors. Recently, commercial tools have become available allowing widespread use of nanomechanical cantilever sensors in these research fields. Here, we will demonstrate the label-free monitoring of dynamic changes during layer formation processes and the characterization of surface structures with nanomechanical cantilevers. The insight into the build-up process of new surface coatings based on nanomaterials provided by cantilever sensors will be demonstrated in particular for the formation of self-assembled monolayers (SAMs) as well as polyelectrolyte multilayers (Layer by Layer formation, LbL).
10:15 AM - BB1.4
Hierarchically Structured, High-Toughness Multilayered Composites from Exponential Layer-by-Layer Assembly.
Paul Podsiadlo 1 , Eugene Kheng 2 , Jungwoo Lee 3 , Kevin Critchley 1 , Ming Qin 1 , Ying Qi 4 , Amit Kaushik 2 , Eric Chuang 1 , Hyoung-Sug Kim 5 , Si-Tae Noh 5 , Ellen Arruda 2 , Anthony Waas 6 , Nicholas Kotov 1 3 4 Show Abstract
1 Chemical Engineering Department, University of Michigan, Ann Arbor, Michigan, United States, 2 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 5 Chemical Engineering, Hanyang University, Ansan, Kyounggi-Do, Korea (the Republic of), 6 Aerospace Engineering, University of Michigan, Ann Arbor, Michigan, United States
10:30 AM - BB1.5
Hierarchical Biomimetic Design of Artificial Muscle Hydrogels.
Megan O'Grady 1 , Po-Ling Kuo 1 , Kit Parker 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Electroactuated polymer hydrogels are promising materials for biological applications, namely because they can operate in physiological solutions at near neutral pH, require low voltages for actuation (1-5 V), are biocompatible, flexible, and can be easily fabricated. Although hydrogels and conductive polymers have been utilized extensively for artificial muscle applications, previous polymer constructs are not engineered to mimic structural and functional aspects of real biological muscle. However, by recapitulating the biological architectures which facilitate contraction in striated muscle, the timescale and magnitude of hydrogel contraction can be greatly improved. We have implemented a hierarchical biomimetic design to significantly enhance the bending of electroactuated hydrogels. In order to decrease Na+ diffusion time, an emulsion polymerization is utilized to create porous hydrogels. These hydrogels display increased bending angles (60-70 degrees) and faster electroactuation than those reported in the literature, demonstrating the importance of optimizing Na+ diffusion to increase hydrogel contraction. In addition, we have arranged the hydrogel into anisotropic patterns at multiple spatial scales (25μm – 5 mm), which can improve hydrogel contraction by controlling the spatial extent of ion diffusion within the polymer milieu. In effect, utilizing a photolithographic technique, we have developed a method to repeatedly and reliably arrange hydrogel architectures at the micro- and macroscale, as well as engineer structural gradients in hydrogels. Overall, our research highlights the need to replicate the multiscale contractile machinery of biological muscle in soft actuator systems. In addition, we have shown that these hydrogels can be used as fast synthetic actuators by toggling the magnitude and polarity of voltage applied in a physiological saline solution. Our results indicate that the actuation of biocompatible, polyelectrolyte hydrogels that can be significantly enhanced by capturing the contractile mechanisms of intact muscle tissue. These hydrogels represent a biocompatible, flexible polymer with rapid, reversible electroactuation in near neutral pH environments, which can be exploited for soft actuator applications in physiological environments.
10:45 AM - BB1.6
Haloform Adsorption on Crystalline Copolymers of Vinylidene Fluoride with Trifluoroethylene.
Carolina Ilie 1 , Jie Xiao 2 , Peter Dowben 2 Show Abstract
1 Physics, SUNY Oswego, Oswego, New York, United States, 2 Physics , University of Nebraska at Lincoln, Lincoln, Nebraska, United States
Reversible bromoform absorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF-TrFE 70:30) was examined by photoemission and inverse photoemission. The adsorption of bromoform on this polymer surface is associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state, whose intensity scales with the unscreened photoemission final state.
11:30 AM - BB1.7
Giant Electrocaloric Effect in Ferroelectric Polymers Near Room Temperature.
Bret Neese 1 3 , Baojin Chu 1 3 , Sheng-Guo Lu 1 , Yong Wang 2 , Eugene Furman 1 , Qiming Zhang 1 2 Show Abstract
1 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Electrical Engineering Department, The Pennsylvania State University, University Park, Pennsylvania, United States
When an electric field is applied to a dielectric material, it will induce a change in its polarization. The consequent changes in the entropy and temperature in the material are referred to as the electrocaloric effect (ECE), which can provide an efficient means to realize solid state cooling devices for a broad range of applications such as on-chip cooling and temperature regulations for sensors and electronic devices. Most research on the ECE focuses on ferroelectric ceramics, in which the polarization mechanism is ionic and temperature and entropy changes are typically too low to be of practical use. Applying an electric field to a polar polymer may induce a large change in the dipolar ordering resulting in a larger entropy change than that associated with ionic displacement in ceramics. Based on D-E loop measurements at varying temperature and using the Maxwell relation between the pyroelectric coefficient and electrocaloric effect (ECE), it is shown that a large ECE can be realized in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer at temperatures above the ferroelectric-paraelectric transition (above 70 ○C). A giant isothermal entropy change (>55 J/kgK) and adiabatic temperature change (> 12 ○C) are observed that are comparable with the giant magnetocaloric effect (MCE) materials. We further show that a similar level of ECE near room temperature can be achieved by working with the relaxor ferroelectric polymer of P(VDF-TrFE-CFE) (CFE: chlorofluoroethylene). The data also reveal that there is a difference in the temperature dependence of ΔS and ΔT between the two classes of ferroelectric polymer systems. That is, the normal ferroelectric P(VDF-TrFE) copolymer displays a decrease of both ΔS and ΔT with temperature at above the F-P transition, whereas in the relaxor ferroelectric P(VDF-TrFE-CFE), both ΔS and ΔT increases with temperature at above the dielectric constant peak in the experiment range investigated. The results presented indicate the potential of polar polymers in achieving high ECE because of the large entropy change associated with the electric field induced dipole ordering-disordering (O-D) process at temperatures near the O-D transformations.
11:45 AM - BB1.8
In-situ Synthesis of Metal Nanoparticles Embedded PDMS Composite Films.
Anubha Goyal 1 , Ashavani Kumar 1 , Pulickel M. Ajayan 1 Show Abstract
1 Mechanical Engineering & Materials Science, Rice University, Houston , Texas, United States
12:00 PM - BB1.9
Application of a Chemically Adsorbed Monomolecular Layer for Increasing the Adhesion Force between Plated Copper Metal and the Resin Substrate.
Yuji Ohkubo 1 , Shogo Ohnishi 1 , Hiroyuki Yamamoto 1 , Kazufumi Ogawa 1 , Satoshi Miyazawa 2 , Kazuhiro Soejima 2 , Akira Nakano 2 Show Abstract
1 Engineering, Kagawa university, Takamatsu, Kagawa, Japan, 2 Business development hq process technology dvlpmt.Center, Alps Electric Co., Ltd., Sendai, Miyagi, Japan
A chemically adsorbed monomolecular layer containing pyrrolyl group (PNN- CAM) was prepared between a plated copper layer and a resin substrate for increasing the adhesion force without roughening a surface of the resin substrate. Although it was not enough to increase the adhesion force between the copper layer and the resin substrate by using only PNN- CAM, the sufficient adhesion force was obtained by preparing a poly-pyrrole thin film between the copper layer and PNN-CAM. The measurements of the film thickness with an ellipsometer, the water contact angles with an automatic contact angle meter, IR spectra with a Fourier Transfer Infrared (FT-IR) spectrophotometer and UV-vis spectra with a ultraviolet-visible (UV-vis) spectrophotometer were performed for characterizing PNN-CAM and the poly-pyrrole thin film on the substrate. Auger Electron Spectroscopy (AES) was also applied in order to analyze the condition of the poly-pyrrole thin film between the resin substrate and the copper layer. The peel strength test was performed in order to evaluate the adhesion force. The best adhesion force was 0.98 [mN/m], and the targeted value 0.60 [mN/m] was sufficiently achieved.
12:15 PM - BB1.10
Copying the Natural Skeletal Muscle Design into a New Artificial Muscle System.
Maria Bassil 1 2 , Michael Ibrahim 1 , Mario El Tahchi 1 , Joseph Farah 1 , Joel Davenas 2 Show Abstract
1 Department of Physics, Lebanese University -Faculty of Sciences II, Fanar, Jdeidet, Lebanon, 2 Laboratoire des Matériaux Polymères et des Biomatériaux, Claude Bernard University -Lyon I, Lyon, Villeurbanne, France
Polyacrylamide (PAAm) is an electroactif biocompatible non biodegradable material; they cannot be absorbed into tissues and cells due to their high molecular weight which make them the most promising candidate for many bio-applications such as implant and artificial muscle[1-2]. The key to exploitation of gels is the design of the system in which they are used. So mimicking the natural skeletal muscle need to create a new design that can regroup the electrical sensitivity, the linear displacement and the fast response while keeping a good mechanical properties . Therefore achieving these goals using a simple low cost and relatively easy to process method is the key to make a real great progress.In this study a new design of an artificial muscle based on hydrolyzed PAAm gel is developed in order to be synthesized using an easy to process method, based on the advantage of fibrous systems and on the linear displacement actuation. This structure converts the electric energy into a linear displacement; it is able to receive electrical information and quickly transmit specific contraction responses.The model consists on a fiber like elements of hydrolyzed PAAM, working in parallel, embedded in a thin conducting gel layer which plays the role of electrodes. Fibers are encapsulated in a braided structure by disposing a thin elastic conductive gel film. The thin film holds the fibers together allowing them to act in parallel while keeping the speed of response, distribute forces to minimize damage of the fibers and provide a conduit for electricity in order to stimulate the fibers. The film deposited in the longitudinal section of fibers is connected to the negative electrode while the film deposited in the cross-section of fibers is connected to the positive electrode. Under an electrical stimulation the fibers contract linearly. Like in natural muscle, as the stimulation increases, the number of fiber in state of contraction increases and the strength of contraction of the whole muscle also increases.Further studies have to be made in order to improve the model efficiency. Y.Osada and JP.Gong (1998) Advanced Materials 10 827 – 837. Y.Bar-Cohen (2001) Electroactive Polymer (EAP) Actuators as Artificial Muscles: Reality, Potential, and Challenges Second Edition, Y.Bar-Cohen, Bellingham, SPIE Press Monograph Vol. PM136. R.Bonser, W.Harwin, W.Hayes, G.Jeronimidis, G.Mitchell and C.Santulli (2004) Final Report, EAP-Based Artificial Muscles as an Alternative to Space Mechanisms ESA/ESTEC Contract No 18151/04/NL/MV.
BB2: Device Application
Tuesday PM, December 02, 2008
Grand Ballroom (Sheraton)
2:30 PM - **BB2.1
Large Deformation and Instability in Electroactive Polymers.
Zhigang Suo 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard, Cambridge, Massachusetts, United States
Subject to a voltage, a layer of a dielectric elastomer reduces its thickness, so that the voltage induces a high electric field. The positive feedback may cause the elastomer to thin down drastically, resulting in electrical breakdown. Furthermore, a recent experiment has shown that the homogeneous deformation of the layer can be unstable, giving way to an inhomogeneous deformation, such that regions of two kinds coexist in the layer, one being flat and the other wrinkled. We show that the free-energy function of a dielectric elastomer is typically non-convex, causing the elastomer to undergo a discontinuous transition from a thick state to a thin state. When the two states coexist in the elastomer, a region of the thin state has a large area, and wrinkles when constrained by nearby regions of the thick state. We also show that the instability can be tuned by the density of cross links and the state of stress.1. Zhigang Suo, Xuanhe Zhao and William H. Greene, A nonlinear field theory of deformable dielectrics. Journal of the Mechanics and Physics of Solids 56, 467-486 (2008).2. Xuanhe Zhao, Wei Hong and Zhigang Suo, Electromechanical coexistent states and hysteresis in dielectric elastomers. Physical Review B 76, 134113 (2007).3. Xuanhe Zhao, Z. Suo, Method to analyze electromechanical stability of dielectric elastomers. Applied Physics Letters 91, 061921 (2007).
3:00 PM - BB2.2
Growth and Characterization of Polymer Based Dielectrics Thin Films and their Application to Si and GaAs MOS Devices.
El Hassane Oulachgar 1 , Cetin Aktik 1 , Mihai Scarlete 2 Show Abstract
1 Department of Electrical & Computer Engineering, Sherbrooke University, Sherbrooke, Quebec, Canada, 2 Department of Chemisty, Bishop's University, Sherbrooke, Quebec, Canada
3:15 PM - BB2.3
Development Of Conductive Polymer Single Layer Cantilever For Conductivity Measurement.
Ping Du 1 , Xi Lin 1 , Xin Zhang 1 Show Abstract
1 Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States
Conductive polymers are an unusual class of organic materials that exhibit some reduction or oxidation (redox) state dependent properties. In this work, we focus on the actuator aspect, where the volume change relies on the ions and solvent flux.Polypyrrole is synthesized electrochemically in a typical three-electrode set up. The synthesis is carried on in 0.1 M pyrrole monomer and 0.1 M sodium dodecylbenzene sulfonate (NaDBS) aqueous solution, and controlled by constant current density of 1 mA/cm2 and 0.5 mA/cm2, respectively. The 1 mA/cm2 current density results in higher and unstable potential which might overoxidize the polymer and create inferior structure, while 0.5 mA/cm2 current density gives very stable potential and not exceed 0.7 V. The following syntheses are all conducted in this value. We further examine the relationship between the polymer thickness and the consumed charge density by varying the synthesis time, from 1 min to 30 min. Exclude the first sample which synthesized in the beginning, all following samples fit very well into a linear manner. Based on this information, we can precisely control the desired polymer thickness simply by adjusting the current density and deposition time.For the micro actuator design, we use two different approaches by standard microfabrication techniques. The bilayer cantilever is similar as Smela’s, using different adhesion method. The anchor part consists of Cr and Au, while the moving part is barely Au on top of glass. Then we apply the sacrificial method for single layer cantilever. Because Ti etchant (typically hydrochloric acid) will attack Cr as well, the under etching of Ti will make the whole structure peeled off from substrate. Therefore we use Au as the sacrificial layer and Ti as the anchor. During the synthesis, polypyrrole first deposit on Au layer, and extend to Ti layer after sufficient time. When the deposition complete, we can easily under etch the Au to release the cantilever, leaving only polypyrrole as the moving part. Without the bending of bilayer, we hope this structure could be used as a linear actuator in future.We also characterize the polypyrrole films by measuring its conductivity in dry state using four point probe station. First we measure the polypyrrole and Au bilayer cantilever. The conductivity ranges from 559 to 1898 S/cm, which can be compared to the value report by other people. While the resistivity is near proportional to thickness, which means the sheet resistance is almost constant. One possible reason could be that the probes may penetrate the polymer so the conductivity is measured from both polymer and gold. So we try to do further measurement by using our single layer cantilever. The preliminary result shows the a series of seven cantilevers synthesized for 10 min have average thickness of 3.0 μm, and the conductivity is very consistent with a average of 5.4 S/cm and standard deviation of 0.0875.
4:00 PM - BB2.4
Composite Electromagnetic Wave Absorber Made of Aluminum Particles or Sendust Particles Dispersed in Polystyrene Medium.
Kenji Sakai 1 , Yoichi Wada 1 , Yuuki Sato 1 , Shinzo Yoshikado 1 Show Abstract
1 Electronics, Doshisha University, Kyotanabe, Kyoto, Japan
4:15 PM - BB2.5
Changes in Morphology and Electrical Properties of Annealed PEDOT:PSS Layers and Their Influence on the Performance of Polymer Blend Photodetectors.
Bettina Friedel 1 , Panagiotis Keivanidis 2 , Neil Greenham 1 Show Abstract
1 Physics, University of Cambridge, Cambridge United Kingdom, 2 Physics, Imperial College London, London United Kingdom
The conducting polymer poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is commonly used as an electrode material in organic photovoltaic devices. It modifies the energy barrier at the hole-collecting electrode, and it also smoothes the relatively rough ITO surface, reducing short circuits. PEDOT:PSS is usually deposited from an aqueous colloidal solution, wherein the colloidal particles consist of a PEDOT-rich core, surrounded by a more insulating PSS shell. The morphology of the deposited PEDOT:PSS film can be modified by annealing, and since PEDOT:PSS is infusible, the temperature limit is set to the onset of degradation at around 350degC. The densification which occurs upon annealing, together with the modification of the PSS shell allows adjustment of the conductivity and workfunction. Here, we demonstrate the effects of PEDOT:PSS annealing in photodetecting devices based on blends of poly(3-alkylthiophenes) with the polyfluorene copolymer poly(9,9-dioctyl-fluorene-co-4,7-di-thiophen-2-yl-benzothiadiazole) (F8TBT). We present AFM and SEM results on morphological changes of the PEDOT:PSS colloidal particles due to different annealing temperatures and the influence on film density. We show how annealing modifies the electrical properties of the film, allowing the overall device performance to be improved.
4:30 PM - BB2.6
Optimization of New Ultralow-k Materials for Advanced Interconnection.
Xuan Li 1 , James Economy * 1 Show Abstract
1 Materials Science and Engineering , University of Illinois at Urbana-Champaign, Urbana , Illinois, United States
The demand for increased signal transmission speed and device density for the next generation of multilevel integrated circuits has placed stringent demands on materials performance. Currently, integration of the ultra low-k materials in dual Damascene requires chemical mechanical polishing (CMP) to planarize the copper. Unfortunately, none of the commercially proposed dielectric candidates display the desired mechanical and thermal properties for successful CMP. A new polydiacetylene thermosetting polymer (PDEB-TEB) which displays a low dielectric constant (low-k) of 2.7 was recently developed. This novel material appears to offer the only avenue for designing an ultra low k dielectric (1.85k), which can still display the desired modulus (7.7Gpa) and hardness (2.0Gpa) sufficient to withstand the process of CMP. In this talk, we will present recent additional studies to further characterize the thermal properties of spin-on PDEB-TEB ultra-thin film. These include the coefficient of thermal expansion (CTE), biaxial thermal stress, and thermal conductivity. Thus the CTE is 2.0*10^-5K^-1 in the perpendicular direction and 8.0*10^-6K^-1in the planar direction. The low CTE provides a better match to the Si substrate which minimizes interfacial stress and greatly enhances the reliability of the microprocessors. Initial experiments with oxygen plasma etching suggest a high probability of success for achieving vertical profiles.
4:45 PM - BB2.7
Investigating A Few Key Issues of Ionomeric Polymer/Conductive Network Composite Electromechanical Transducers.
Sheng Liu 1 2 , Minren Lin 2 , Wenjuan Liu 3 , Ralph Colby 3 2 , Qiming Zhang 1 2 Show Abstract
1 Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
We investigate ionomeric polymer/conductive network composite (IPCNC) electromechanical transducers, in which the ions moving in and out of the IPCNC generate electromechanical transduction. We especially investigate a few issues which are crucial to realize high performance IPCNC transducers, i.e., development of extensional actuators and raising the electric field level in the device while keeping the applied voltage below one or two volts. It is noted that while the applied voltage is limited to below the electrochemical reaction threshold, there is no limit on the electric field level allowed in the composites, which can be increased markedly by working with thin composites and developing multilayer actuators. It is further demonstrated that the device speed is proportional to 1/d^2, where d is the individual layer thickness, and hence the actuator speed and efficiency can be improved significantly in thin layer actuators. In addition, by properly choosing the ionic liquid with optimized ion sizes, the actuator efficiency can be further improved.
5:00 PM - BB2.8
Tuning Threshold Voltage and Off Current in Organic Transistors by Precharging Gate Dielectrics with Electron Microscope and Corona Sources.
Howard Katz 1 , Kedar Deshmukh 1 , James West 2 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Electrical Engineering and Computer Science, Johns Hopkins University, Baltimore, Maryland, United States
For plastic electronics applications, it is necessary in some cases to ensure consistent transistor switching voltages throughout a circuit, and in other cases it is desirable to produce controlled but contrasting switching voltages among transistors with the same materials and dimensions. We perform corona charging of gate dielectrics, especially polymers such as CYTOP® (a heavily fluorinated polymer) and poly(methyl methacrylate), prior to completing field effect transistor fabrication using thiophene oligomer and polymer semiconductors. This results in threshold voltage shifts and off-current increases, from a combination of static charging and surface reactions. Static charging is assessed by Kelvin probe measurements and surface reactions are evident by changes in contact angles and photoelectron spectra. We further found that a scanning electron microscope source serves as a novel, regiodefined, and chemically cleaner tool for carrying out the charging of gate dielectric polymers, again prior to deposition of the semiconductor and source-drain contacts. Shifts of tens of volts, on the same order as the threshold voltage shifts, with no deleterious change in off current or mobility are observed. Surface analyses reveal that morphology and surface functionality are maintained. Contrasting transistors can be fabricated just millimeters apart, differing only in proximity to the charging source during the charging process. Translation of this method to printed organic circuitry will be discussed.
5:15 PM - BB2.9
Micropatterning of a Photocurable Hydrogel in a Microfluidic System.
Huijie Hou 1 , Arum Han 1 Show Abstract
1 Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States
Thermoresponsive hydrogels such as poly(N-isopropylacrylamide) (PNIPAAm) that can swell and deswell under external stimulus are attractive materials for applications such as cell release in tissue engineering, actuation of miniaturized components, and active controlling of surface properties. Micropatterned hydrogels show improved thermoresponsiveness compared to bulk hydrogels. Microfabricated hydrogel structures have been integrated into various miniaturized systems such as cell arrays or as actuation mechanisms. Current methods of hydrogel micropatterning are either through the use of photopolymerization combined with a photolithography mask or require sophisticated fabrication steps and equipments. Direct photopolymerization is a simple micropatterning method but generating high density arrays of hydrogel microstructures are challenging. Hydrogel microstructures with short distances tend to be connected to each other due to UV light scattering during photopolymerization. Hydrogel microstructures smaller than few tens of micrometers are also challenging to make due to their poor adhesion to substrates that results in micropillar detachment from substrates during the uncured hydrogel washing step. The softness and weak mechanical strength of most hydrogels make small microstructure formation even more challenging. We present here a method for fabricating several micrometer scale microstructures with high density and large area coverage using a maskless photopolymerization method combined with hydrophilically patterned hydrophobic substrates. Photoresist was first patterned to form the microstructure arrays (diameters: 15 μm ~ 200 μm, separations: 0 μm ~ 200 μm) on a glass substrate and then treated by trichlorosilane to make the area not covered by the photoresist patterns hydrophobic. The photoresist patterns were then removed in acetone, resulting in a hydrophobic substrate with arrays of hydrophilic spots. Microfluidic channel arrays made of poly (dimethyl siloxane) was placed on the substrate covering the hydrophilic spots, PNIPAAm injected into the microchannels, followed by flushing out the prepolymer hydrogel solutions at a controlled flow rate using a syringe pump. The hydrogel prepolymer solution remained only at the hydrophilic spots due to the surface tension and was subsequently cured under an UV light. Features down to 5 μm in diameter were successfully patterned to fully cover a 4 cm X 5 cm area with PNIPAAm micropillar arrays. Feature sizes could be controlled by adjusting the flushing speed of PNIPAAm pre-polymer solution and channel height of the microchannels. The developed method provides a simple and easy way of creating high density thermoresponsive hydrogel microstructure arrays covering a large surface and can be used to control the thermoresponsiveness and surface properties of such a surface.
5:30 PM - BB2.10
On the DC Breakdown Mechanism of P(VDF-HFP) Capacitor Films with High Electrical Energy Density.
Xin Zhou 1 , Shihai Zhang 1 , Qin Chen 1 , Yong Wang 1 , Chen Zou 1 , Qiming Zhang 1 Show Abstract
1 Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Polarpolymers with high dipole density have the potential to achieve very high electric energy density Ue, required in many modern electronics and electric systems. We demonstrate that by combining the nonpolar to polar molecular structure changes, a very high Ue (>25 J/cm3) can be obtained in defects modified poly(vinylidene fluoride) polymers, such as P(VDF-CTFE) (CTFE: chlorotrifluoroethylene), and P(VDF-HFP) (HFP: hexafluoropropylene). In this study, the DC breakdown mechanism of P(VDF-HFP) capacitor film was investigated systematically over a wide range of film thickness, temperature, and voltage ramp rate. It was found that above room temperature the DC breakdown strength decreases with temperature while below room temperature, it is nearly a constant. At room temperature, the DC breakdown strength increases with voltage ramp rate and but does not depend on the film thickness. The experimental results and theoretical simulation suggest that different breakdown mechanisms may be dominant at different temperature regions.
5:45 PM - BB2.11
Earthworm Inspired Locomotion from Thermoresponsive Organic-Inorganic Hybrid Hydrogels.
Hitesh Arora 1 2 , Rahul Malik 1 , Lilit Yeghiazarian 3 , Claude Cohen 2 , Ulrich Wiesner 1 Show Abstract
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca , New York, United States, 3 Biological Engineering, UCLA, Los Angeles, California, United States
Transformation of energy into directed motion requires different forms of complexity at different length scales. Nature demonstrates several mechanisms for inducing motion, at different length scales, through various organisms. It is desirable to mimic these natural systems to make efficient devices for MEMS and microfluidics. Although devices based on biological systems have demonstrated that directed motion can be induced using ATP powered biomolecules such as motor proteins, the stringent physiological conditions required limit the applicability of such systems. In contrast, a synthetic material may provide the necessary robustness and freedom to tune parameters as per the requirements. Responsive materials such as polymer hydrogels are ideal for such a device. The responsive nature has been exploited in the past to make devices for applications ranging from drug delivery to micro-valves.Previously, we developed a prototype device based on thermoresponsive hydrogels that mimics the earthworm locomotion. The mechanism involves shrinking and swelling small segments of a long gel, induced by volume phase transition through a simple temperature stimulus using peltier elements, an effect generated in the earthworm by flexing and stretching of muscles along the body. The shrinking segments moves the body forward while swollen segments hold the surface to prevent the moving body from slipping. The device, capable of generating directed motion at velocities of order 10 µm/sec and cargo carrying capability, had some limitations pertaining to mechanical robustness, long ionization times to induce large volume changes, slow swelling kinetics and slippage leading to imperfect motion. Here we show a new device, based on the same working principle, which overcomes these challenges. The device is made of super-porous, organic-inorganic hybrid hydrogels that show large volume phase transitions above 32°C without requiring additional ionization and show fast swelling kinetics that allow the gels to come back to their initial size in short times. With these gels, confined in rough capillary walls, we were able to generate efficient slip-free motion, over multiple cycles and with velocities of order µm/sec. In comparison, one of the fastest crawling eukaryotes, Amoebae of Acrasis (with cell surface area of 759 µm2), moves with an average speed of 71.6 µm/min. Since the time scale for shrinking and swelling decreases as the critical dimension of the gel becomes smaller, the velocity of gel motion is expected to increase dramatically by decreasing the diameter of the gel. We anticipate that the principle described herein might be widely utilized in a variety of areas in biotechnology, microfluidics, small-scale robotics and drug delivery.
Zhongyang Cheng Auburn University
Qiming Zhang The Pennsylvania State University
Siegfried Bauer Johannes-Kepler University Linz
Debra A. Wrobleski Los Alamos National Laboratory
BB3: New Materials and Characterization
Wednesday AM, December 03, 2008
Grand Ballroom (Sheraton)
9:00 AM - **BB3.1
Multiferroic Magnetoelectric Polymer-Based Composites.
Ce-Wen Nan 1 Show Abstract
1 Materials Science & Engineering, Tsinghua University, Beijing China
9:30 AM - BB3.2
Ferroic Nanofiber Yarns for Nanofluidic Applications.
Kostya Kornev 1 , Taras Andrukh 1 , Igor Luzinov 1 Show Abstract
1 School of Materials Science & Engineering, Clemson University, Clemson, South Carolina, United States
Magnetic nanofilaments are making recent publications; described as long flexible chains made of magnetic colloids and linkers, these particles have already been used in self-propulsion of bodily cells and DNA. Typically, diameter of these filaments is measured in nanometers, hence their applications are limited to nanomechanical systems. The major barrier to fabricate microscopic magnetic or ferroelectric filaments is that the flexural rigidity and magnetization/polarization cannot achieve high values simultaneously. In this paper, we discuss new approach which avoids these problems. Highly porous (~ 83%) polyvinylidene difluoride (PVDF) / polyethylene oxide (PEO) nanofibers of about 50-500 nm in diameter were prepared by electrospinning. Wetting experiments and theoretical analysis suggest that nanofibers have a core-skin morphology (PEO as a core and PVDF as a skin). Assembling these nanofibers in the yarns, we produce materials with high tenacity, which can be bent, knotted, or twisted without any breakage. Results of DSC, TGA, and FTIR characterization of the produced yarns reveal the presence of crystalline PVDF β-phase responsible for ferroelectric properties of the material. These yarns can be made magnetic by impregnating them with magnetic nanoparticles. Since the yarns are very flexible and field responsive, they can be irreversibly bent and twisted. A series of experiments show that ferroic yarns can be used as conduits and collectors in nanofluidic devices. Probing aerosol droplets, biofluids from capillaries, making operations on single cells, are only a few applications under consideration.
9:45 AM - BB3.3
Low Loss Magnetodielectric Polymer Nanoparticle Composites for Radio Frequency (RF) Applications.
Ta-I Yang 1 , Leo Kempel 2 , Peter Kofinas 3 Show Abstract
1 Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland, United States, 2 Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan, United States, 3 Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, United States
The aim of this research is to develop polymer nanocomposites with improved dielectric permittivity (ε), magnetic permeability (μ), and low energy loss at radio frequencies. Surfactant-modified iron oxide and nickel zinc ferrite nanoparticles of various sizes were successfully synthesized by a seed-mediated growth method. The free precursor ions present during synthesis is the major factor contributing to the growth of larger particles. The dielectric permittivity and magnetic permeability of the resultant block copolymer (styrene-b-ethylene/butylene-b-styrene) nanoparticle composites increased with increasing amount of doped nanoparticles. However, the magnetic permeability of the composites was significantly influenced by the size of the doped nanoparticles. The optimum size range for magneto-dielectric particles to obtain high magnetic permeability is between 30 and 100 nm, where single domain ferromagnetic particles without any domain walls are present. Polymer nanoparticle composites using softer nickel zinc ferrite nanoparticles exhibited higher magnetic permeability (μ=2) with lower dielectric loss tangent (tan δ<0.01) at 1 GHz.
10:00 AM - BB3.4
Polyaniline Nanostructures for Hydrogen Storage Applications.
Sesha Srinivasan 1 , Michael Jurczyk 1 , Ayala Phani 2 , Ashok Kumar 1 , Yogi Goswami 1 , Elias Stefanakos 1 Show Abstract
1 , University of South Florida, Tampa, Florida, United States, 2 , NANO-RAM Technologies, Bangalore India
Polyaniline nanostructures such as nanofibers and nanospheres have been synthesized using chemical templating and electrospun techniques in presence of surfactants as dopants. The reversible hydrogen sorption characteristics namely kinetics, pressure-composition isotherms and life-cycle measurements were performed on these polyaniline (PANI) nanostructures at high hydrogen pressures and room temperatures. The rapid uptake and release of hydrogen (~95% of hydrogen uptake in less than 10 minutes) was observed and this may be due to the unique nanostructures of polyaniline fabricated in the present study. The structural, microstructural, chemical and optical characterizations were compared and correlated with the observed hydrogen sorption behavior in these polyaniline nanostructures.
10:15 AM - BB3.5
Pattern Transformation in Periodic, Porous, Elasto-plastic Microstructures.
Srikanth Singamaneni 1 , Katia Bertoldi 2 , Sehoon Chang 1 , Ji-hyun Jang 3 , Edwin Thomas 3 , Mary Boyce 2 , Vladimir Tsukruk 1 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Materials Science and Engineering and Institute of Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Single and multi-component periodic porous micro and nanostructures have attracted increased attention over the last two decades owing to their current and prospective applications in photolithography, photonics, phononics, microfluidics, sensors, and scaffolding. When these microstructures are stressed, their periodic porous geometry can suddenly change at a critical point due to mechanical instability of the structural elements leading to dramatic reorganization of organized microstructures. We present the recent observation of the sudden transformation of periodic microporous structures of a crosslinked epoxy-based Novolak photoresist fabricated by interference lithography. The mechanical instability is brought about by polymerization of acrylic acid onto the porous microframe structures. The results of a numerical investigation confirm the critical role of the compressive stresses developed in the microframe structure. In striking contrast to the earlier observations of elastic instabilities in porous elastomeric structures, the elastic-plastic nature of the crosslinked microstructure studied here provides the ability to dramatically transform the original geometry and lock in the new pattern.
10:30 AM - BB3.6
Operation Characteristics of Ionic Polymer-Metal Composite using Ionic Liquids.
Kunitomo Kikuchi 1 , Masafumi Miwa 2 , Shigeki Tsuchitani 3 Show Abstract
1 Graduate School of Systems Engineering, Wakayama University, Wakayama-shi Japan, 2 Institute of Technology and Science, The University of Tokushima, Tokushikma-shi Japan, 3 Department of Opto-Mechatronics, Faculty of Systems Engineering, Wakayama University, Wakayama-shi Japan
Recently, it was reported that Nafion-based ionic polymer-metal composite (IPMC) using ionic liquids (ILs) could operate in air. In this study, we evaluated operation of IPMCs using 1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMIBF4), 1-buthyl-3-methyl-imidazolium tetrafluoroborate (BMIBF4), and 1-buthyl-3-methyl-imidazolium hexafluorophosphate (BMIPF6) as ionic liquids. Among IPMCs using three kinds of ILs, IPMC using BMIPF6 had the largest displacement in air under an application of a rectangle waveform voltage (±2.0V) with a frequency of 0.5Hz. Compared with the previously reported Flemion®-based IPMC using BMIBF4, Nafion®-based IPMC using BMIBF4 exhibited a curvature of 0.6m-1, which was approximately a half of that of the Flemion®-based IPMC (1.5m-1). On the other hand, the curvature of Nafion®-based IPMC using BMIPF6 was almost same as that of Flemion®-base IPMC using BMIBF4. In the previous study concerning Flemion®-based IPMC, the one using BMIBF4 had larger displacement than that using BMIPF6. This difference of the performance between Nafion®-based and Flemion®-based IPMCs using the same kinds of ILs might be based on difference in molecular structure and electrical affinity to ILs of the both ion exchange materials. We found that the behavior of IPMC using ILs changed depending on environmental humidity. In all evaluating conditions, slope of response curves at initial stage (the initial response speed) increased with increase in humidity and the applied voltage. Increase in the initial response speed at higher humidity and higher applied voltage, is probably due to increase in moving speed of counter ions in IPMC in these conditions. It is thought that mobility of counter ions in IPMC increased with increasing humidity. To estimate equivalent circuit of IPMC using ILs and to investigate influences of the derived circuit parameters on the operation of IPMC, we evaluated frequency dependence of complex impedance of IPMC. Complex impedance plane plots (Cole-Cole plots) of IPMC were preferred at higher frequencies over 5.0Hz. In all measurement conditions, the complex impedances were plotted in semicircular shape. This result might indicate that the equivalent circuit of IPMC is expressed by a parallel combination of resistance element and capacitance element in this frequency range. The curvature of IPMC using IL was larger than that of IPMC having lower resistance element. The value of resistance element of IPMC decreased with increase in environmental humidity. This means that ionic conductivity of the Nafion® membrane increased with increasing environmental humidity. It is thought that the increase in ionic conductivity at higher humidity resulted in the increase in the initial response speed, as described in above. This work was supported in part by Grant-in-Aid for Scientific Research C (No. 18560249) from Japan Society for the Promotion of Science (JSPS). J. Wang et al., Proc. SPIE, Vol. 6168, 61680R (2006)
10:45 AM - BB3.7
α to β Phase Transformation in Nanocomposites of Poly (Vinylidene Fluoride) Doped with Silver Nanoparticles.
Daniel Miranda 1 , Vitor Sencadas 1 , Ana Sanchez-Iglesias 2 , Isabel Pastoriza-Santos 2 , Luis Liz-Marzan 2 , Jose Gomez Ribelles 3 4 5 , Senentxu Lanceros-Mendez 1 Show Abstract
1 Departamento de Física, Universidade do Minho, Braga Portugal, 2 Dept. de Química Física, Universidade de Vigo, Vigo Spain, 3 3Centro de Biomateriales, Universidad Politécnica de Valencia, Valencia Spain, 4 Regenerative Medicine Unit, Centro de Investigación Príncipe Felipe, Valencia Spain, 5 , 5CIBER en Bioingeniería, Biomateriales y Nanomedicina, Valencia Spain
11:30 AM - BB3.8
Enhanced Ferroelectric Properties of Electrospun Polyvinylidene difluoride-based Nanocomposites: Towards Multiferroic Materials.
Jennifer Andrew 1 , David Clarke 1 Show Abstract
1 Materials, University of California- Santa Barbara, Santa Barbara, California, United States
Multiferroic materials exhibit both ferromagnetic and ferroelectric properties, which tend to be mutually exclusive in single-phase materials. Therefore, composite materials are the obvious approach to developing a material with both a high electric permittivity and high magnetic permeability. In composite systems the magnetoelectric effect arises from the mechanical coupling between magnetostrictive and piezoelectric phases. Magnetoelectric coupling in composite systems is an interfacial phenomenon. To enhance this coupling, the interfacial area between the two phases should be maximized. This can be accomplished using nanoparticles, which have a large surface area-to-volume ratio. Ceramic multilayer multiferroic materials are plagued with porosity and cracking at the interfaces between the two phases, resulting in reduced performance. To avoid the limitations of these ceramic composites, ferroelectric polymer- magnetic nanoparticle (PVDF-Ni0.5Zn0.5Fe2O4) composites with enhanced properties were prepared via electrospinning.
Polyvinylidene difluoride (PVDF) fibers with continuously dispersed ferrite (Ni0.5Zn0.5Fe2O4) nanoparticles were prepared by electrospinning from dimethyl formamide (DMF) solutions. The ferrite nanoparticles were synthesized using aqueous coprecipitation routes, and were subsequently functionalized with an organo-silane, forming stable ferrofluids in DMF. The effects of the electrospinning processing conditions and nanoparticle loading on the fiber morphology, crystallinity and the crystalline structure of PVDF were investigated. SQUID magnetometer and dielectric measurements were also performed to determine the materials’ magnetic and dielectric properties.
Electrospinning provides a simple one- step technique to form PVDF in the ferroelectric β- phase directly from solution. The average fiber diameter can be tuned from 150nm to 2 microns by adjusting the processing parameters. We have shown that the amount of β-phase can be enhanced by the addition of a well-dispersed nanoparticle phase. The fraction of β-phase increases with increased nanoparticle loading, with a maximum fraction of β- phase, F(β)max, of 1.
11:45 AM - BB3.9
``Smart" Surfaces of Polymer Brushes.
Dong Meng 1 , Qiang Wang 1 Show Abstract
1 Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado, United States
12:00 PM - BB3.10
Dielectric Breakdown of Transformer Insulation Materials Under Cryogenic and Room Temperatures.
Horatio Rodrigo 1 , Danny Crook 1 , Steve Ranner 1 , Richard Liang 1 2 , Aniket Ingole 1 2 Show Abstract
1 Center for Advanced Power Systems, Florida State University, Tallahassee, Florida, United States, 2 Industrial Engineering, Florida State University, Tallahassee, Florida, United States
The results of breakdown voltage measurements on "ThermaVolt", a material used in power transformers is presented. The performance of this material is compared with others that consist of polymer resins that have been modified by the addition of nano-particles. The polymers are Epoxies with the addition of Barium Titanate and Alumina. The breakdown voltage measurements have been conducted under 60 Hz AC high voltage and high voltage impulse voltage with standard lightning waveform.The electrode configuration gives a uniform field with 25 mm diameter electrodes made of Stainless Steel with Bruce profile. Measurements presented are at room temperature 293 K and at Liquid Nirtogen temperature 77 K.
12:15 PM - BB3.11
Bilayer Microactuator of Two Kinds of Polypyrroles Doped with Different Dopants.
Shigeki Tsuchitani 1 , Kosei Chikatani 2 , Kunitomo Kikuchi 2 Show Abstract
1 Department of Opto-Mechatronics, Wakayama University, Wakayama-shi Japan, 2 Graduate School of Systems Engineering, Wakayama University, Wakayama-shi Japan
Many applications of conjugated polymers as soft actuators are being proposed, since they have many excellent characteristics compared with conventional inorganic actuators, such as light weight, large deformation and low operation voltage. Recently, microactuators using conjugated polymers, which are fabricated by MEMS (Micro Electro Mechanical Systems) technology, are attracting much attention, aiming at realization of micro-valve, micro-pump, microrobot arm, etc.We fabricated a bilayer microactuator of two kinds of polypyrroles (PPys) doped with different dopants, i.e., dodecylbenzenesulfonic acid (DBS) and p-phenolsulfonic acid (PPS), on a silicon substrate using surface micro-machining technology. The fabricated actuator was 0.5mm long, 0.2mm wide and 1μm thick. It bended about 90 degree under an application voltage of 0.7V in an aqueous solution of sodium hexafluorophosphate (NaPF6).In the fabrication of the microactuator, a patterned chromium layer (thickness: 5nm), which had a function of an adhesion layer to fix the microactuator on the substrate, was formed on the silicon substrate at first. After that, a gold layer (thickness: 100nm) was deposited both on the chromium layer and the bear silicon substrate, and pattered to the shape of the microactuator. Then, PPy doped with PPS (PPy(PPS)) was deposited on the pattered gold layer potentiostatically in an aqueous solution of pyrrole (0.25M/l) and PPS (0.15M/l). Furthermore, PPy doped with DBS (PPy(DBS)) was successively deposited on the PPy(PPS) layer potentiostatically in an aqueous solution of pyrrole (0.25M/l) and DBS (0.15M/l).The fabricated microactuator was actuated in the aqueous solution of NaPF6 (1M/l) by applying a voltage of 0.7V between the gold layer and a counter electrode. In the first voltage application, the gold layer which constructed the microactuator, peeled away from the silicon substrate except the contacting part with the chromium layer and bent about 90 degree in about 18s, since adhesion force between gold and silicon is enough smaller than that between gold and chromium. After the second voltage application, the microactuator bent stably having a response speed of about 5s. Since the main components of the fabricated microactuator are two kinds of polypyrroles doped with the different dopants and the thickness of the gold layer was enough smaller than that of polypyrrole layers, the effects of ductility of the gold layer on the operation of the microactuator is very small. As a result, the stable operation of the microactuator is expected.
BB4: Device Application