Nanosize latex particles via miniemulsion polymerization

The mechanisms of miniemulsion formation, stabilization, and polymerization were studied both experimentally and theoretically. The subdivision of miniemulsion droplets was investigated as a function of homogenization energy. The stabilization of droplets against Ostwald ripening has been explained on a thermodynamic basis. Miniemulsions and their corresponding latexes were synthesized and characterized for particle size and surface coverage by surfactant titration, as well as polymerization rate using calorimetry. Equations relating the surface properties and reaction kinetics to particle diameters were developed. The particle nucleation mechanism was established under varying free surfactant conditions. Nanosize latex particles (<50 nm) have been synthesized using less surfactant and/or costabilizer than previous researchers.; The interfacial area in a miniemulsion prepared by sonification increased linearly with time according to an energy balance equation, and the droplets were shear-limited in size. Droplet diameters were reduced substantially after a single pass through a Microfluidizer, but did not change significantly after additional passes, indicating that the droplets were surfactant-limited in size.; Miniemulsion droplets were stabilized more effectively against Ostwald ripening by increasing the costabilizer amount or decreasing the costabilizer molecular weight. The initially broad droplet size distribution narrows considerably during polymerization as the result of monomer redistribution by a polymer concentration gradient. Hexadecane was more effective as a costabilizer than cetyl alcohol or predissolved polymer, and stabilized the miniemulsion droplets over a period of several hours.; The free surfactant concentration increased as surfactant was added, until the critical micelle concentration was exceeded at 60 mM SLS, and micellar nucleation occurred simultaneously with droplet nucleation. Most of the surfactant was on the surface of the droplets (80%) or particles (95%). The fractional surface coverage on the droplets was the same as on the corresponding latex particles. The droplet diameter in a low-solids miniemulsion was greatly reduced as a result of the high ratio of surfactant to monomer. The maximum rate of polymerization varied with the number of particles to the 0.59 power, and the kinetics were explained mathematically as an extension of Smith-Ewart kinetics. The rate of miniemulsion polymerization was expressed as a function of temperature using an Arrhenius equation.