Effects of Nanoparticle Interfacial Additives on Phase Inversion of Pickering Emulsions

Abstract

Understanding the effects of interfacial additives such as surface-active nanoparticles on phase inversion of Pickering emulsions is important from a practical point of view. In this work, we studied the effects of surface-active starch nanoparticles on catastrophic phase inversion of Pickering emulsions by continuous addition of a dispersed phase. Two types of experimental grade starch nanoparticles were used: hydrophilic starch nanoparticles (HSNP) and hydrophobic starch nanoparticles (HOSNP). The effects of unmodified and modified bentonite nanoclays (with various degrees of surfactant modification) on the catastrophic phase inversion of water-in-oil (W/O) emulsion to oil-in-water (O/W) emulsion was also determined experimentally. The bentonite nanoclay (NC-Bt) was suspended in the aqueous phase and the critical volume fraction of water where phase inversion of W/O to O/W emulsion took place was determined through conductivity measurements. Cetyl trimethyl ammonium bromide (CTAB) was used as a surfactant to modify the nanoclay. The adsorption of CTAB on nanoclay had a strong influence on the contact angle and the critical volume fraction of water where phase inversion took place. The modification of the nanoclay brought about by the adsorption of CTAB increased the three-phase contact angle (measured through the aqueous phase), thereby making it more hydrophobic.