Polymerization in direct mini-emulsions is a relatively new polymerization technique which allows the preparation of submicron latex particles within the range 100<particle diameter<500 nm This process involves the generation of a large population of submicron monomer droplets in water (termed the mini-emulsion) by intensive shear force with the aid of an adequate emulsifier and coemulsifier (or hydrophobe) These stable, homogenized monomer droplets have an extremely large surface area and, therefore, can compete effectively with the monomer-swollen micelles, if present, for the oligomeric radicals generated in water Monomer droplets may thus become the predominant loci for particle nucleation and polymerization This article presents a review of the current literature in the field of radical polymerization of conventional monomers and surface-active monomers in direct mini-emulsion systems Besides a short introduction into some kinetic aspects of radical polymerization in direct emulsion, mini-emulsion and micro-emulsion systems, we mainly focus on the particle nucleation mechanisms and the common and different features between the classical emulsion and finer mini-emulsion polymerization systems The effects of the type and concentration of initiator, emulsifier, coemulsifier (hydrophobe) and monomer are evaluated The influence of the complex formation, the close-packed structure, etc within the mini-emulsion droplet surface layer on the colloidal stability, the nature of the surface film, and the radical entry process are summarized and discussed These results show that the nature of the coemulsifier (hydrophobe), the weight ratio of emulsifier to coemulsifier, the mechanisms of sonification, the stability of monomer droplets, and the presence or absence of free micelles play a decisive role in the polymerization process

Radical Polymerization in Direct Mini-Emulsion Systems

Interfacial aspects of miniemulsions and miniemulsion polymers

2002 Roy W. Tess Award

Emulsification by Surfactants

Kinetic study of the mini-emulsion polymerization of styrene

The emulsification of styrene monomer using mixed-emulsifier systems comprising a fatty alcohol with either sodium lauryl sulfate or hexadecyltrimethylammonium bromide was studied by conductometric titration. The most stable miniemulsions were formed at emulsifier molar ratios between 1:1 and 1:3 when the alcohol had the same chain length as that of the emulsifier. Other factors such as temperature, mixing time, addition rate of the styrene, stirring speed, and composition of the oil phase were also found to affect emulsion stability.

W.L Grimm

Papers

The role of low concentrations of ionic emulsifier—fatty alcohol mixtures in the emulsification of styrene