Energy landscapes for interfacial colloidal crystallization on three-dimensional surface topographies

Designing conditions to enable interfacial colloidal crystallization on three-dimensional (3D) surface topographies requires understanding how particles interact with each other, surfaces, solution species, and gravity. The net interaction, or potential energy landscape, can produce diverse states including dispersed, aggregated, deposited, arrested, and sedimented configurations, often more easily than near-equilibrium interfacial crystalline states. Although nearly neutrally buoyant particles at fluid interfaces have been well studied, less progress has been made in determining competing interactions necessary to produce interfacial colloidal crystals on fluid-solid surface topographies. In this work, we directly measure and model the interactions that control interfacial colloidal crystallization on 3D surface topographies with varying elevation and curvature. Our results demonstrate crystallization for different colloidal materials and sizes in solvent mixtures containing charged surfactants without density or refractive index matching. Conditions for interfacial crystallization are designed via systematic development of direct measurements and models of kT-scale energy landscapes balancing buoyancy, electrostatics, and depletion interactions. Unique crystal morphologies are obtained for different particle materials and dimensions, which shows a dependence on the balance of gravitational and pair interactions.