Polymerization in Microemulsion Systems

Abstract

Polymerization of monomers in microemulsion systems has achieved widespread attention in recent days [1–11]. This new type of polymerization can be considered as an extension of emulsion polymerization [12]. Microemulsions are the colloidal dispersion of oil and water stabilized by certain alkali metal soaps, conventionally known as surfactants [13, 14] (Fig. 1). A microemulsion may be either oil continuous, where water is solubilized in oil phase (i.e., water-in-oil); or water continuous, where oil is dispersed in water, making it an oil-in-water microemulsion. Microemulsions differ completely from macroemulsions or miniemulsions in respect to their thermodynamic stability. Macroemulsions, conventionally known as emulsions, are opaque, milky, and thermodynamically unstable mixtures of two immiscible liquids having droplet size more than 100 nm. Microemulsions, on the other hand, are isotropic, transparent or translucent, and thermodynamically stable systems. This is due to the low interfacial tensions between oil and water microdomains. It is supposed that these microemulsions exist in the form of droplet structure having sizes in the range of 10–30 nm. However, a bicontinuous lamellar structure has also been postulated which is consistent with their transparency [15, 16].