(497b) Charging of Hydrophobic Polymer Particles By Basic Surfactants in a Nonpolar Liquid

Charging in nonpolar liquids is not common because of the large Born energy associated with ions in media of low dielectric permittivity. However, surfactants are known to reduce this energy cost and promote electric charging by increasing the effective ion size. Surfactants not only raise the conductivity of nonpolar bulk liquids but also cause surface charging of dispersed colloidal particles. Although particle charging in nonpolar liquids has been exploited in many practical applications such as electrophoretic image displays or electrostatic lithographic printers, the underlying mechanisms are still not understood. We discuss the charging of polymer particles in alkanes mediated by polyisobutylene succinimide-based surfactatns with systematic structural variations. The surface properties of the particle and surfactant polar head were characterized using the energy parameters of the van Oss-Chaudhury-Good (vOCG) theory of surface energy components. Based on the acid-base parameters of the interacting condensed phases and the electrophoretic mobility observed by phase analysis light scattering (PALS) for the charged particles and the particle-free micellar solutions, we propose that the charging of polymer surfaces may be achieved mainly by asymmetric adsorption of micellar ions. We discuss a hypothetical mechanism for the formation of micellar ion pairs with size asymmetry, and point out characteristic differences between the surfactants-mediated charging of hydrophobic polymer surfaces and that of hydrophilic surfaces in nonpolar liquids.