An In Situ Look at Interfacial Controls on Crystallization and Self-Assembly in Inorganic and Biomolecular Systems

Interfaces play a critical role in solution-based phenomena, such as ion segregation, mineral nucleation, and biomolecular and colloidal self-assembly. The interface alters the distribution of water and ions from that of the bulk, introduces an interfacial free energy that largely determines the free energy barrier for nucleation, and creates an entropic repulsion that acts like a volume exclusion force to drive colloidal assembly. The origin and characteristic length scales of these phenomena are inherently atomic-to-molecular but are manifest in ensemble dynamics and outcomes. Moreover, processes like nucleation and self-assembly arise from fluctuations, making the events that must be probed transient in nature. Consequently, in situ imaging techniques that can capture structure and its evolution, particularly at high speed, are required to build a quantitative picture of such processes. Here I use examples from and in situ TEM, high-speed AFM and fast force mapping studies of interfacial structure, nucleation, and assembly in inorganic and biomolecular systems to elucidate the mechanisms by which interfaces direct these processes, leading to unique pathways, materials and morphologies. The results reveal the importance of surface charge, chemical gradients, colloidal forces, molecular mobility, and solvent organization near interfaces in determining how ordered materials emerge from the solution.