(476e) Engineering the Pinning, Interactions, and Assembly of Colloids at Fluid Interfaces Using Roughness

In this talk, we discuss the disparate ways in which particle surface roughness on spheres and ellipsoids impacts the interfacial pinning, capillary interactions, mechanics, and assembly of particle monolayers. We use a seeded emulsion polymerization technique to produce polystyrene microspheres and microellipsoids with controlled surface topography. By monitoring the dynamics of two particles approaching one another, we find that rough ellipsoids exhibit a strikingly shorter-range capillary interaction potential than smooth ellipsoids. In situ interferometry measurements of the fluid deformation surrounding a single particle quantitatively confirm the decrease in capillary interaction energy and point to roughness-induced changes to interfacial pinning as the mechanism for reduced attraction. This results in a capillary cloaking effect, where rough ellipsoids are interfacially invisible to one another at separations where their smooth counterparts would normally strongly attract. We further explore how controlling particle roughness on both spheres and ellipsoids dictates the interfacial mechanics and microstructural assembly of particle monolayers. In particular, the reduction in interparticle capillary attraction between rough ellipsoids minimizes the propensity for kinetically arrested particle aggregation, allowing the assembly of close-packed, anisotropic, ordered particle monolayers. These results have profound implications on the design and tunability of Pickering emulsions, foams, and the development of anisotropically ordered 2D materials.