Hydrodynamic Signatures of Nanoparticle-Laden Oil-Water-Solid Interfaces

Abstract

This research scrutinizes a multidisciplinary subject focusing on the in-situ formation of materials at oil-water interfaces and their effects on dynamics of liquid-liquid and liquid-solid interfaces. In particular, the formation of emulsions at oil-water interfaces is investigated in the presence of silica nanoparticles in the water and sorbitan monooleate surfactants in the oil. Then, the influence of in-situ generated emulsions on dynamics of (i) double emulsion/bicontinuous phase formation, (ii) drop pinch-off, and (iii) drop spreading are thoroughly examined. In the low viscosity oil, the spontaneous formation of multiple core-shell emulsions is reported. However, for the oils with a viscosity higher than 60 mPa.s, interconnected structures of oil and microemulsion phases are formed in a fraction of a second. The classical Plateau-Rayleigh instability in the presence of in-situ generated emulsions at the silica dispersion-high viscosity surfactant solution interfaces is revisited. The aqueous phase is injected vertically through a nozzle into a surfactant solution reservoir. The injection of DI-water generates single droplets. While in the presence of silica nanoparticles, a variety of flow morphologies from single droplets to straight liquid columns are observed. It is shown that the pinch-off of the silica nanoparticle dispersion droplet occurs in an elasto-capillary regime. The viscoelastic emulsion layer resists the capillary force and attenuates Plateau-Rayleigh instability, forming silica dispersion filaments. A scaling analysis based on the evaluation of the relative importance of the residence time to the required time for forming emulsions and the diffusion of emulsions from interface to bulk is conducted to identify required conditions for generating liquid filaments. Finally, filaments are used as inks for creating liquid letters and liquid-fluidic channels.In the last part of this dissertation, the effect of surfactants and nanoparticles on the spreading dynamics is examined. Silica nanoparticles at a concentration above 2.0 wt. % increase the early time spreading rate and the final wetted area. Increasing the surfactant concentration in the oil phase results in a plethora of wetting conditions from fully spreading to non-sticking. In the non-wetting system, the droplet levitates on a layer of oil which is used as a transport vehicle for depositing interfacial nanodroplets.