Pickering Emulsion Formation of Paraffin Wax in an Ethanol-Water Mixture Stabilized by Primary Polymer Particles and Wax Microspheres Thereof.

Stable dispersions of paraffin wax droplets and their nano- and microspheres have broad applications. Despite intensive efforts, the production of uniform wax spheres remains a challenge. For their preparation, abundant surfactants and other additives are commonly used to stabilize the dispersions. These additives are hardly removable and entrain often adverse consequence in many applications, particularly in biological and medical applications, where microspheres with absolutely clean surface are preferred. We report here a novel process to prepare stable dispersion of wax droplets in a water-ethanol mixture with a narrow size distribution by simply shaking without any surfactants. The process is featured by using primary polymer particles (PPs) of poly(dodecene-trihydroxymethylpropane triacrylate) as a Pickering stabilizer. PPs were prepared by precipitation polymerization without any surfactant and stabilizer. By rapidly cooling the wax emulsion, solid wax spheres with good uniformity were obtained. Their size, between 50 and 480 μm, was easily adjustable by changing the shaking rate, number of PPs, and particularly the size of PPs. The morphology of the wax spheres was examined by SEM, which showed that they were covered by a layer of PPs. The formation mechanism of the microspheres was also discussed on the basis of the adsorption energy of PPs on wax spheres, estimated from the corresponding contact angle of the solvent toward the PPs and the wax. This paper presents a novel pathway for the preparation of wax microspheres with only polymer particles without the need for any other additives.