Cationic gemini surfactants with oligo(oxyethylene) spacer groups and their use in the polymerization of styrene in ternary microemulsion

The aggregation and phase behavior, micelle and microemulsion structure, and the polymerization behavior of various binary and ternary systems containing water, (oligooxa)alkanediyl-alpha,omega-bis(dimethyldodecylammonium bromide) surfactants (12-EOx-12), and styrene are reported. The hydrophilic spacer chain length x in the cationic gemini surfactants was varied between 0 and 5. With increasing spacer chain length the surface area per molecule at the air-water interface increases, whereas the single-phase region of the ternary microemulsion systems is largest for x being 1 and decreases with increasing x in the investigated concentration range. Small-angle neutron scattering (SANS) and cryogenic temperature transmission electron microscopy (cryo-TEM) measurements indicate that the micelle and microdroplet dimensions decrease with increasing x. Polymerization was carried out at 25 and 60 degrees C using Co-60 gamma-rays. Spherical polystyrene particles in the nanometer size range were obtained, the particle size being dependent on the spacer length of the gemini surfactants and on the polymerization temperature. At 25 degrees C, particle size and molecular weight of polystyrene were maximum at medium spacer length, while at 60 degrees C, the particle size decreased with increasing x, in correspondence to the microstructural properties of the microemulsions observed by SANS. The experimental results suggest that the chemical structure of the surfactant molecules used in the microemulsion formulation has a strong influence on the particle properties after polymerization. This influence depends on the curvature of the interfacial film induced by the surfactant molecules.