Influence of Surfactant-Nanoparticle Interactions on Emulsion Behavior with Applications to Flow Assurance

Abstract

Emulsions have wide industrial applications such as those in paints, cosmetics, food, energy, and pharmaceuticals. The surfactant-nanoparticle interactions play a critical role in determining the stability of the interfacial film. My research aims at probing the fundamental mechanisms governing the surfactant-nanoparticle interactions at the fluid-fluid interface and the consequence of surfactant-nanoparticle interactions on the stability and rheology of emulsions. My research consisted of four parts: a) probing the influence of nanoparticle addition to surfactant-stabilized emulsions b) elucidating the effect of surfactant addition to nanoparticle-stabilized emulsions c) investigating the influence of surfactant-nanoparticle interactions on the behavior of oil-in-oil emulsions d) examining the influence of surfactant-nanoparticle interactions and nanoparticle wettability on hydrate formation.

Literature shows that the presence of both surfactants and nanoparticles enhance emulsion stability. On the contrary, our data showed that the addition of silica nanoparticles to surfactant-stabilized emulsions could lead to destabilization of water-in-oil emulsions. Partially hydrophobic silica nanoparticles had higher destabilization efficiency as compared to hydrophilic and hydrophobic silica nanoparticles.

Our results showed that the addition of surfactants significantly influenced the droplet size of Pickering emulsions depending on the wettability of nanoparticles at the liquid-liquid interface. For water-in-oil emulsions stabilized using hydrophobic nanoparticles, there was a significant decrease in the droplet size upon the addition of a surfactant. On the contrary, for water-in-oil emulsions stabilized using partially hydrophobic nanoparticles, no significant change in the droplet size was observed upon the addition of a surfactant. Based on our data, we postulate that the addition of a non-ionic surfactant aided in partial displacement of hydrophobic nanoparticles from the oil-water interface unlike partially hydrophobic nanoparticles, which in turn affected the droplet size of emulsions.

Furthermore, our results showed that simultaneous emulsification using hydrophobic nanoparticles and a surfactant (either Span 80 or Triton X-100) resulted in a single-step formation of multiple oil-in-oil-in-oil (O/O/O) emulsions. Multiple O/O/O emulsions had lower viscosity when compared to simple oil-in-oil (O/O) emulsions. Simple O/O emulsions had a lower degree of shear thinning behavior when compared to multiple O/O/O emulsions.

In addition, our results showed that nanoparticle wettability influenced the formation and rheology of hydrates in water-in-oil emulsions.