Emulsifying properties, of block copolymers. Oil‐water emulsions and microemulsions

Abstract

Abstract The emulsifying effect of poly(styrene‐b‐ethylene oxide) block copolymers (Cop PS‐PEO) has been studied for the toluene‐water system as a function of the molecular characteristics of the copolymer (composition, molecular weight, and structure). To demonstrate the surfactive properties of Cop PS‐PEO, we determined the interfacial tension γ i for the toluene‐water system in the presence of these block copolymers. For oil/water (O/W) and water/oil (W/O) emulsions, prepared in the presence of Cop PS‐PEO, we determined the phase inversion point, the particle size of the dispersed phase, the stability and the viscosity as a function of the PEO content, the molecular weight, and the structure of the block copolymers. It appeared that the best results for the emulsification are obtained with Cop PS‐PEO having molecular weights less than 100, 000. Stable O/W emulsions of small particle size are preferentially prepared with di‐ or triblock copolymers having a PEO content of 60‐80 percent. In contrast, stable W/O emulsions are obtained with diblock copolymers having a PS content of 60‐80 percent. The difference in behavior between diand triblock copolymers also showed the importance of the chain conformation at the toluene‐water interface. As an extension, we have shown that microemulsions can be obtained with such polymeric surfactants. Isopropanol and butylamine appeared to be efficient cosurfactants for the system water/toluene/Cop PS‐PEO.