(553e) Entropic Control over Nanoscale Colloidal Crystals

Globally ordered colloidal lattices have broad utility in a wide range of novel optical and catalytic devices, for example, as photonic bandgap materials. However, the self-assembly of stereospecific structures is often confounded by defects. Small free energy differences different crystal polymorphs, making it difficult to produce a single morphology at will. Current techniques to handle this problem usually rely on energy minimization; many colloids have been computationally engineered with anisotropic pairwise interactions to achieve morphological control. However, the complexity of these designs often makes experimental realization difficult. In this presentation, I plan to summarize recent computer simulation work enabled by efficient  GPU-centric codes on the effects of polymeric co-solutes on crystallizing colloidal suspensions. These can be used to direct colloidal structures by relying upon the polymer's entropic interactions resulting from the interplay between the polymer's internal degrees of freedom and the void structure of a material. This represents a novel design paradigm that has the potential to significantly simplify control over colloidal polymorphism. I will elaborate on how to rationally design the cosolute structure to thermodynamically stabilize a single desired polymorph in a binary mixture, and the consequences that thermal perturbations have on this effect. I will then offer insights into how to design temperature dependent cosolute “switches” that allow the stability of a polymorph to be controlled via†experimentally accessible parameters.