Polystyrene latexes in a size range of 30−180 nm can be synthesized by polymerization in miniemulsions where the particle size responds to the amount of the surfactant sodium dodecyl sulfate (SDS) which was varied between 0.5 and 50 wt % with respect to monomer. Turbidity and surface tension measurements were used to characterize the miniemulsification by ultrasonication and the approach to a steady state of droplet size. Since size equilibrium seems to be established by a rate equation of collision-induced droplet fusion and ultrasound fission, miniemulsions realize the minimal droplet size for the distinct amount of surfactant; i.e., they are “critically stabilized” with respect to collisions (τ2 process). Complete stability against Ostwald ripening (τ1 process) is obtained by the addition of a hydrophobe, which was varied over a broad structural range. The efficiency of this hydrophobic agent is given mainly by a very low water solubility. The growth of the critically stabilized miniemulsion droplets is usually slower than the polymerization time; therefore in ideal cases, a 1:1 copy of droplets to particles is obtained, and the critically stabilized state is frozen. The critical surface coverage of these particles with SDS molecules was determined and depends strongly on the particle size:  the smaller the particle size, the higher the required surface coverage with surfactant. The good accessibility of these systems allows to establish a general relation between the macroscopic surface tension of the latex and the microscopic coverage of the particles which is expected to hold true for all latexes. Finally, the characteristics of polymerization in miniemulsions were compared with those of the corresponding processes in macro- and microemulsions.

This paper reports on the convenient one-step synthesis of hollow polymer nanocapsules by miniemulsion polymerization of different monomers in the presence of larger amounts of a hydrophobe. The idea of the procedure is that the hydrophobe and monomer form a common miniemulsion, whereas the polymer is immiscible with the hydrophobe and demixes throughout polymerization to form the hollow polymer structure surrounding the hydrophobe. The primary objective of this work was to study the effect of different monomers and monomer mixtures, of the type and amount of surfactant, and of the hydrophobe on the morphological characteristics of the polymer/oil composite particle, using dynamic light scattering, scanning and transmission electron microscopies, and atomic force microscopy. It was found that the structure can be adjusted to cover the whole range from independent particles over partially engulfed structures to structurally integer nanocapsules of high uniformity.

Polymer dispersions made of a variety of monomers, including styrene, butyl acrylate, and methyl methacrylate, were generated by the miniemulsion process in the presence of a coupling comonomer, a hydrophobe, and silica nanoparticles. Depending on the reaction conditions and the surfactants employed, different hybrid morphologies were obtained, comprising a "hedgehog" structure where the silica surrounds the latex droplet and provides stabilization even without any low molecular weight surfactant. In other parts of the composition diagram noncoupled structures as well as "raspberry" hybrids where whole clusters of silica nanoparticles are completely embedded in the polymer particle can be made. The resulting structures are promising for a number of applications, e.g. the increase of scratch resistance in water-based coatings.