(669e) Interfacial Interactions in Oil/Brine Emulsions Stabilized By Combinations of Cellulose Nanocrystals and Emulsion Stabilizers

Oil/Brine emulsions were prepared and stabilized using a combination of negatively charged cellulose nanocrystals (CNC) and emulsion stabilizers of various charges. Dodecane was used as the oil phase, while two high salinity brines were used as aqueous phases, namely, synthetic sea water (SSW) and American Petroleum Institute (API: 2wt% CaCl₂ + 8wt% NaCl) brine. Emulsions prepared using either nanoparticles or surfactants have been extensively characterized and the interfacial phenomenon involved in stabilization of these emulsions are well documented. Emulsions and emulsion based products that use a combination of both nanoparticles and surfactants have various applications in oil and gas production, as well as environmental cleanup; understanding interactions between nanoparticles and emulsion stabilizers in such emulsion systems is thus very important. This study was designed to characterize mechanisms by which CNCs and emulsion stabilizers interact to stabilize oil-water emulsions. Both CNCs (1 wt.%) and surfactants (at concentrations just below their critical micelle concentration) were dispersed in the aqueous phase prior to emulsion formation. The critical micelle concentrations of the stabilizers were measured in each brine, both with and without nanocrystals, to study adsorption behavior of surfactant molecules onto the CNC surface using a force tensiometer. Representative samples with volume ratios of 25:75 and 90:10 aqueous to oil phase were prepared using high shear mixing. The oil rich emulsions have potential applications for oil/gas production, while the water rich emulsions are relevant for oil spill cleanup. These emulsions were then characterized as either O/W (oil in water) or W/O (water in oil) based on electrical conductivity measurements. It was found from the measurements that at low oil to water volume ratio all emulsions were of O/W type but as the relative volume of the oil phase increased they switched to W/O. The stabilities of the prepared emulsions were studied in terms of macroscopic creaming rates over the duration of 24 hours and by quantifying the size distribution of the dispersed droplets with an optical microscope. Two formulations, guar gum with CNC and CNC alone, stabilized the emulsions for longer times compared to charged surfactants mixed with CNC. Droplets for the most stable emulsions tested were smaller in size and uniform in distribution, indicating that they are able to withstand coalescence. Interfacial tension measurements of the brine/dodecane system were used to estimate the adsorption of CNC and surfactants onto the interface using the pendant drop method. The results indicate that using non-ionic stabilizer and CNC with minimal interaction between them can be used to significantly improve stability of dodecane/brine emulsion.