Dual-responsive poly(styrene-alt-maleic acid)-graft-poly(N-isopropyl acrylamide) micelles as switchable emulsifiers

Self-assembled polymeric micelles can be used as efficient particulate emulsifiers. To explore the relationship between micellar structure and emulsification performance, pH- and temperature-responsive self-assembled micelles were prepared and used as emulsifiers, based on a novel grafted polymer poly(styrene-alt-maleic acid)-graft-poly(N-isopropyl acrylamide) (PSMA-g-PNIPAm). Structure of PSMA-g-PNIPAm micelles varies in response to pH and temperature changes and can be classified into four typical states, including shrunken, moderately swollen, extremely swollen, and inverted states, confirmed by a combination of electrophoresis, dynamic light scattering (DLS), transmission electron microscopy (TEM), and H-1 NMR. This structural variation plays a key role in the emulsification performance of PSMA-g-PNIPAm micelles, according to the emulsifying characteristics of the four typical PSMA-g-PNIPAm micelles as well as the micellar morphologies on the surface of oil droplets as observed by SEM. Emulsions stabilised by micelles with moderately swollen structure are especially stable compared with either the shrunken micelles or the extremely swollen micelles, because the moderately swollen micelles combine the advantages of solid particulate emulsifiers and polymeric surfactants. (C) 2012 Elsevier Inc. All rights reserved.