Quantitative considerations for the formulation of miniemulsions

摘要

The polymerization of sty-rene in miniemulsions stabilized with anionic sodium dodecyl sulfate or nonionic Lutensol AT50 results in stable polymer dispersions with particle diameters between 30 and 480 nm and narrow particle size distributions. Steady-state mini-emulsification results in a system "with critical stability", i.e. the droplet size is the product of a rate equation of fission by ultrasound and fusion by collisions, and the mini-droplets are as small as possible for the timescales involved. The droplet growth by monomer exchange, or the τ_1 mechanism, is effectively suppressed by addition of a very hydro-phobic material, whereas droplet growth by collisions, or the τ_2 mechanism, is subject to the critical conditions. 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.