Effects of Bidisperse Wettability on Interfacial Viscoelasticity of Particle Laden Interfaces

Increasing use of Pickering Emulsions has led to increasing study of interfacial particles. It is known that particle contact angle determines emulsion type and modifies interfacial viscoelasticity, effecting emulsion stability and viscosity. Most studies of particle interfaces examine a mono-population of colloids. However, in applications, there can be significant distribution in contact angle. What role such distribution plays on interfacial mechanical properties is unclear.

In this work, the effects of controlled dispersity of wettability on particle laden interfaces is examined. Using hydrophobic and hydrophilic negative polystyrene and hydrophobic non-ionic polystyrene, mixed wettability systems with varying ratios of hydrophobic to hydrophilic particles are studied. An increase in interfacial elasticity is observed when the ratio of hydrophobic to hydrophilic particles reaches 1. This corresponds with an increase in local hexagonal order and decrease in area around particles. Similar but smaller magnitude changes are observed for combinations of hydrophobic particles. We believe these changes occur due partitioning of particles to either side of the interface, creating larger local density and increased resistance to deformation.