Nanoemulsions with enhanced temperature stability using thermo-sensitive association of nonionic surfactant and amphiphilic polyelectrolytes

Aqueous mixtures containing a non-ionic surfactant (tetraethylene glycol monododecylether, C12E4), an amphiphilic polymer (poly(sodium acrylate) hydrophobically modified with azobenzene groups randomly attached along the chains, HMPA) and 0.3 M NaNO3 were studied regarding the associations between macromolecules and surfactant assemblies (micelles or lamellar phases) at various temperatures (4–37 °C). The effects of the thermo-induced transition of surfactant assemblies from micelles to lamellar phase on phase separation behavior were systematically investigated as a function of surfactant and polymer concentration, polymer structure (amount of grafted hydrophobic groups) and temperature. Rheological properties of polymer-rich coacervates revealed thermo-thickening behavior, in accordance with phase separation behavior. Finally, bulk phenomena were applied to design nanoemulsions with improved temperature stability taking the opportunity of strengthening interfacial layers through thermo-thickening properties.