Interfacial Dynamics of Confined Microgel Liquids on Soft Surfaces

While much research has strived to understanding the dynamics of confined liquids on a hard solid surface, the dynamics of liquids confined on a soft and deformable surface remains unclear. In this work, we employed poly(N-isopropylacrylamide) (PNIPAM) microgels of varied crosslinking density as the confined liquids as well as confining surface coatings. We analyzed the mean-squared-displacement (MSD) of confined PNIPAM microgel particles in the first 1-2 particle layers immediately adjacent to PNIPAM coated surface of varied particle-to-surface elasticity ratios. We observed that soft surface of low elasticity show little impact on the interfacial dynamics of confined microgel particles of varied elasticity, where the MSD of confined microgels exhibits little deviation from their bulk behaviors. Such interfacial behavior is in sharp contrast to the dynamic arrest of microgels confined on hard surface of high elasticity. Furthermore, we found that the dynamic heterogeneity in confined glass-like microgel liquids could diminish with decreasing the elasticity of confining surface, which gives insight to design low-friction and lubricious coatings and surfaces.