Crystallization of Polymer-Grafted Nanoparticles (PGNPs) Induced by Polymer Additives and Kinetic Pathways of PGNP Interfacial Assembly

Growing nanoparticle (NP) crystals has been pursued extensively using ligand chemistries such as DNA and supramolecules, controlled evaporation and patterned surfaces. In this talk, I will introduce a precipitation-induced NP crystallization process where a trace amount of polymeric impurities (&lt;0.1 wt.%) leads to reproducible, rapid growth of high quality 3-D NP crystals in solution and on patterned substrates with high yield. The polymers preferentially precipitate on the PGNP polymeric surfaces inducing the formation of small PGNP clusters, which subsequently act as nuclei to initiate PGNP crystal growth in dilute solution. Formation of 3-D PGNP crystals can be tuned by varying polymeric additives loading, solvent evaporation rate and NP size. This study elucidates how to balance cohesive energy density and PGNP diffusivity in the self-assembly to favor nuclei formation energetically and kinetic growth in dilute solutions.<br/>Further structural diversity is achieved by enabling co-crystallization of two types of PGNPs into binary crystals. Kinetic process of binary PGNP assembly at liquid-air interface is captured by <i>in-situ</i> X-ray scattering combined with <i>ex-situ</i> TEM characterization, featuring a polymer-like autophobic dewetting process to lower surface energy. Nanoscale microphase separation within binary PGNP mixtures is followed by surface-induced particle reorganization. Metastable structures form through stacking of PGNP layers and short-range diffusion, which can further form “frustrated” lattices. Alternatively, equilibrium crystals nucleate and grow through lattice distortion depending on the compatibility of the preferred local order and global crystalline order. This study helps illustrate the process of how different interactions interplay and influence the final structures and provide guidelines for hierarchical functional materials fabrication.