Franca Tiarks

Encapsulation of Carbon Black by Miniemulsion Polymerization

Full Paper: In this paper the effective encapsulation of carbon black with polymers by co-sonication of a carbon black dispersion and a typical miniemulsion polymerization recipe is described. The carbon containing polymer particles are analyzed in detail by particle size measurements, transmission electron microscopy, density distributions experiments with the ultracentrifuge, and by nitrogen adsorption. The final particle size was in the range of 50 to 170 nm, the weight ratio polymer to carbon was changed between 20 : 80 and 90 : 10. In all cases, the surface tension of the final dispersion is above the minimal surface tension of SDS indicating the absence of micelles and the incomplete coverage of the polymer coated carbon particles with surfactant. The amount and type of an added hydrophobe needed for osmotic stabilization as well as the type of monomer have a large influence on the encapsulation process. The encapsulation process can be described by a scenario where the fusion/fission by ultrasound splits the monomer droplets, whereas the monomer coated carbon stays intact. The thickness of the monomer film depends on the amount of monomer and has to be optimized since there is an optimal range of monomer layer thickness in order to preserve the morphology. Too low amounts of monomer result in incompletely covered particles which aggregate with polymer whereas too much monomer results in the formation of a second species of pure polymer particles. The process can be described as a polymerization in an adsorbed monomer layer created and stabilized as a miniemulsion (“ad-miniemulsion polymerization”).

Polyaddition in miniemulsions: A new route to polymer dispersions

Polyaddition reactions in miniemulsions were successfully performed by miniemulsification of mixtures of di-, tri-, and tetra-epoxides with varying diamines, dithiols, or bisphenols, and subsequent heating to 60°C. This expands the potential applications of the family of miniemulsification techniques to generate aqueous polymer dispersions, since miniemulsions were previously just employed for the radical polymerization of vinylic monomers. Depending on the chemical nature of the monomers, the amount of surfactant, and the pH of the reaction mixture, latex particles with diameters between 30 and 600 nm and sometimes very narrow particle size distributions were obtained. Gel permeation chromatography (GPC) measurements on the final polyaddition products reveal molecular weights of about 20 000 with a polydispersity index of close to 2, i. e., close to ideal reaction conditions are preserved throughout the heterophase reaction.

The controlled generation of nanosized structures in miniemulsions

In this article the effective encapsulation of carbon black with polymers by cosonication of a carbon black dispersion and a miniemulsion is decribed. The inverse miniemulsion process is shown to be an excellent method for the preparation of particles consisting of hydrophilic polymers.