Encapsulation of carbon black by miniemulsion polymerization

In this paper the effective encapsulation of carbon black with polymers by co-sonication of a carbon black dispersion and a typical miniemulsion polym erization recipe is described. The carbon containing polymer particles are analyzed in detail by particle size measurements, transmission electron mic roscopy, 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 mi nimal surface tension of SDS indicating the absence of micelles and the inc omplete coverage of the polymer coated carbon particles with surfactant. Th e amount and type of an added hydrophobe needed for osmotic stabilization a s well as the type of monomer have a large influence on the encapsulation p rocess. The encapsulation process can be described by a scenario where the fusion/fission by ultrasound splits the monomer droplets, whereas the monom er 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 ra nge of monomer layer thickness in order to preserve the morphology, Too low amounts of monomer result in incompletely covered particles which aggregat e with polymer whereas too much monomer results in the formation of a secon d species of pure polymer particles. The process can be described as a poly merization in an adsorbed monomer layer created and stabilized as a miniemu lsion ("ad-miniemulsion polymerization").