Stimuli-responsive emulsions stabilized by polymeric surfactants

We present physicochemical routes to the development of soap-free simple emulsions (n-dodecane-water) stabilized by ion-containing polymers as primary emulsifiers. First, we show how to control the type of emulsion (oil-in-water or water-in-oil) using a series of hydrophobically modified poly(sodium acrylate)-based polymers with a broad range of hydrophilic-lipophilic (HL) properties. The relevant parameters used to monitor the emulsion type are the degree of hydrophobic modification of the emulsifier, the type of the hydrophobic moiety, the ionic strength and pH of the system. We also present original results demonstrating how light can be used as a new trigger to set the emulsion type. Light-induced control is obtained using an appropriate combination of a photo-responsive (PR) polymer and an amphiphilic polyelectrolyte possessing well-balanced HL properties. The chromophore groups along the PR polymer allow the adjustment of its hydrophobicity upon irradiation and, hence, the overall hydrophobicity of the system. In turn, the macroscopic consequence of the effect of irradiation results in the control of the emulsion type. (C) 2003 Society of Chemical Industry.