Evaporation-induced nucleation and growth of colloidal crystals

Colloidal crystals are functional materials whose optical, electronic, or catalytic activity can be controlled by their microscopic structure. One convenient method to fabricate colloidal crystals is to disperse the colloids... [ view full abstract ]

Colloidal crystals are functional materials whose optical, electronic, or catalytic activity can be controlled by their microscopic structure. One convenient method to fabricate colloidal crystals is to disperse the colloids in solution and evaporate out the solvent. This typically yields a polycrystalline close-packed material whose structural characteristics depend on processing conditions in ways that are not fully understood. We performed massive-scale, explicit-solvent molecular dynamics simulations to study the evaporation-induced nucleation and growth of such crystals. We used a machine learning technique to discover and classify relevant structures in the simulation trajectories. Our algorithm uses graph theory to autonomously infer structural relationships between particles according to their local topology, allowing us to quantify the crystalline character of particles near defects, grain boundaries, and interfaces.

We showed how the crystal nucleates and grows from the drying air-solvent interface by evaluating structural evolution during the crystallization process. Complementary implicit solvent simulations were performed to demonstrate the nontrivial role that solvent plays in controlling several key phenomena. Our work has important implications for the processing of colloidal crystals from solution and non-equilibrium molecular modeling. Developing a full understanding of the self-assembly process could unlock new tools for directed self-assembly by leveraging non-equilibrium effects to select between structures with similar equilibrium free energies.