Using Contactless Interfacial Rheology to Probe Interfacial Mechanics for Compositional Ripening

In this study, we investigate the impact of modifying colloid-colloid interactions on the rheological properties of a layer of poly(methyl methacrylate) PMMA colloids at a dodecane-water interface. Toluene is introduced into the oil phase in order to modify attractive interactions between colloids. We first make qualitative observations of water-in-oil emulsions undergoing compositional ripening, demonstrating how the addition of toluene modifies the evolution. Without toluene, water droplets finally "explode"; with the addition of toluene, they instead form connected colloidal structures. We secondly employ a novel contactless interfacial setup to probe the rheological properties of a PMMA colloid-laden water-dodecane interface, examining the effects of toluene addition. We find that the interface becomes significantly weaker and more flexible following addition of toluene, contrary to what one might expect for increasing interparticle attractions for high surface coverage interfaces.