Synergistic Formation and Stabilization of Oil-in-Water Emulsions by a Weakly Interacting Mixture of Zwitterionic Surfactant and Silica Nanoparticles

Abstract

Oil-in-water emulsions were formed and stabilized at low amphiphile concentrations by combining hydrophilic nanoparticles (NPs) (i.e., bare colloidal silica) with a weakly interacting zwitterionic surfactant, caprylamidopropyl betaine, to generate a high hydrophilic-lipophilic balance. The weak interaction of the NPs with surfactant was quantified with contact angle measurements. Emulsions were characterized by static light scattering to determine the droplet size distributions, optical photography to quantify phase separation due to creaming, and both optical and electron microscopy to determine emulsion microstructure. The NPs and surfactant acted synergistically to produce finer emulsions with a greater stability to coalescence relative to the behavior with either NPs or surfactant alone. As a consequence of the weak adsorption of the highly hydrophilic surfactant on the anionic NPs along with the high critical micelle concentration, an unusually large surfactant concentration was available to adsorb at the oil-water interface and lower the interfacial tension. The synergy for emulsion formation and stabilization for the two amphiphiles was even greater in the case of a high-salinity synthetic seawater aqueous phase. Here, higher NP adsorption at the oil-water interface was caused by electrostatic screening of interactions between (1) NPs and the anionic oil-water interface and (2) between the NPs. This greater adsorption as well as partial flocculation of the NPs provided a more efficient barrier to droplet coalescence.

Viscosity and stability of ultra-high internal phase CO2-in-water foams stabilized with surfactants and nanoparticles with or without polyelectrolytes

“…Also, the strong capillary interactions between neighbouring particles at the liquid menisci may stabilize lamella against coalescence. 34 The reduction of particle charge with surfactant adsorption as shown in Figure S1 may result in particle flocculation, which is known to provide a greater steric barrier for lamella stability against coalescence, as well as raise the continuous phase viscosity to slow down drainage (Figure 3d), as seen for silica and hexadecyltrimethylammonium bromide, 46 as well as silica and caprylamidopropyl betaine 54 .…”

Novel and Environmentally Friendly Oil Spill Dispersant Based on the Synergy of Biopolymer Xanthan Gum and Silica Nanoparticles

“…39,49,55 In a previous study, highly stable oil−in− seawater emulsions was achieved with addition of 0.5% w/v silica nanoparticles and 0.1% w/v caprylamidopropyl betaine. 30 Binks et al prepared stable emulsions with no oil released within 6 months using 2 wt % silica nanoparticles and SDS as an emulsifier. 44 The lower silica concentration used here means a possible reduced adverse effect of fine nanoparticles on marine organisms.…”

Stabilization of Oil-in-Water Emulsions with Noninterfacially Adsorbed Particles

“…Binks et al have demonstrated interactions between negatively charged silica and positively charged surfactant, and vice versa, as a route to stable Pickering emulsions. 16,17 Interaction between surfactants and hydrophilic nanoparticles (no affinity for the oil-water interface) has indeed been exploited by a number of researchers for its ability to enhance emulsion stability, 16,[18][19][20][21][22] and induce emulsion phase inversion. 10,23,24 In this work, the combination of bare (fully water wet) or surface modified (partially wet by both the oil and water phases) silica nanoparticles (NPs) with surfactant, at concentrations where neither component can form a stable emulsion alone, is shown to form stable emulsions via synergistic effects.…”