Nucleation under soft confinement: Role of polymer-solute interactions

Nucleation of a crystalline phase almost always occurs at interfaces. However, the lack of fundamental understanding of the impact of interfacial properties on nucleation hinders the design of nucleation active materials for regulating crystallization in practice. In particular, the role of intermolecular interactions is often neglected in nucleation under confinement such as those provided by nano- and microporous materials. Herein, we report the use of a novel material, polymer microgels with tunable microstructure and chemistry, for understanding the role of intermolecular interactions in nucleation under confinement and for controlling crystallization from solution in general. We demonstrate that by tuning the polymer-solute interactions, solute nucleation kinetics were promoted by up to 4 orders of magnitude. Moreover, the effect of polymer-solute interactions was manifested by the split of nucleation time scales due to the presence of nucleation sites of distinct chemical compositions in the microgels, characterized by small angle neutron scattering. Our mechanistic investigations suggest that the polymer matrix facilitates nucleation by enhancing effective solute-solute interactions due to solute adsorptive partitioning and by promoting molecular alignment inferred from preferred crystal orientations on polymer surfaces. Our results provide new insights into nucleation at interfaces and help enable a rational material design approach for directing nucleation of molecular crystals from solution.