17 - Stability of Oil-in-Water Emulsions in Polymer–Surfactant Complexes. Paraffin–Water Emulsions in Mixtures of Poly-(Vinyl Alcohol) with Cetyltrimethyl Ammonium Bromide or Sodium Dodecylbenzene Sulphonate

Abstract

Abstract Interfacial tension (γ) measurements at the paraffin oil-water interface at 25°C showed a marked change in the γ–log C curve for both CTABr and NaDBS as PVA was added to the surfactant solutions. Transitions similar to those previously obtained at the air–water interface were obtained. These changes were attributed to the interaction between PVA and CTA + or DBS − ions at the interface forming a “polyelectrolyte”-like complex and/or mixed micelles. The interaction between polymer and surfactant at the interface could also be illustrated by zeta-potential measurements. By using mixtures of PVA and CTABr or NaDBS, much finer emulsions than those obtained with PVA alone were obtained, especially at high surfactant concentrations. In the absence of surfactants, the rate of coalescence K decreased with increase in PVA concentration. At low CTABr concentrations ( −3 mol dm −3 ) the rate of coalescence sometimes increased on addition of PVA. However, at high CTABr concentrations (≥ 6 × 10 −3 mol dm −3 ) addition of PVA reduced K below the value obtained with CTABr or PVA For the PVA–NaDBS system, addition of PVA always reduced K to below the value obtained in NaDBS and at 1000 ppm PVA, K was also lower than with PVA alone at all NaDBS concentrations.