(704c) Evaporation-Induced Assembly of Colloidal Crystals

Colloidal crystals have promising applications for technologies such as photonics, catalysis, and sensing. One convenient method to create such crystals is to disperse the colloids in solution and evaporate out the solvent, leaving behind a close-packed structure. In most situations, however, the crystal structures that form after evaporation are polycrystalline and highly sensitive to the processing conditions. For example, Cheng and Grest [J. Chem. Phys. 138, 064701 (2013)] used computer simulations to show that in-plane crystalline order at the air-solvent interface undergoes a maximum with respect to evaporation rate. The influence of evaporation on crystal structure at larger scales, e.g, across multiple crystalline layers, is not fully understood.

We performed massive-scale, explicit-solvent molecular dynamics simulations to study the evaporation-induced nucleation and growth of a colloidal crystal. We classified the structure of crystallizing colloids using a machine-learning approach, and showed how the crystal nucleates and grows from the drying air-solvent interface. Complementary implicit solvent simulations were performed to demonstrate the nontrivial role that solvent plays in controlling the crystallization process. Our work has important implications for the processing of colloidal crystals from solution and nonequilibrium molecular modeling.