Synergistic Stabilization of Emulsions and Emulsion Gels with Water-Soluble Polymers and Cellulose Nanocrystals

The effect of water-soluble polymers on the properties of Pickering emulsions stabilized by cellulose nanocrystals (CNCs) was investigated. Pretreatment of CNCs with excess adsorbing polymer, hydroxyethyl cellulose (HEC) or methyl cellulose (MC), gave smaller and more stable dodecane-in-water emulsion droplets compared to either polymer or CNCs alone, i.e., synergistic stabilization. By contrast, dextran, which does not adsorb on CNCs, gave unstable emulsions, with or without CNCs. CNCs with HEC or MC produced emulsions that showed no significant creaming or phase separation over several months. Interfacial tension, quartz crystal microbalance and confocal laser scanning microscopy measurements indicate that both HEC and MC are surface active and adsorb onto CNCs. 75% of the oil-water interface is covered by CNC particles coated with HEC or MC and the remaining interface is stabilized by HEC or MC chains not bound to cellulose. Viscoelastic emulsion gels were also produced by adding excess MC to the CNC-HEC emulsions and heating above 70 degrees C. The thermogelation was reversible, and multiple cycles of heating/cooling did not lead to coalescence of the emulsion. This work points to broad application of CNCs with water-soluble polymers as promising green emulsion stabilizers for food, pharmaceutical, and cosmetic products.