Charge carriers created by interaction of a nonionic surfactant with water in a nonpolar medium

Abstract

Electric charging phenomena in nonpolar media are crucial in various industrial fields such as the development of oil-based electrophoretic inks or flow assurance in petroleum handling. Despite a number of hypothetical mechanisms, the exact pathway for electric charging is still a matter of ongoing research. In the present study, we consider charge carriers in a nonpolar medium, particularly those created by the interaction of a nonionic surfactant with water, to shed some light on the mechanistic pathway for the electric charging process. First, it is shown that a nonionic polyisobutylene succinimide amine surfactant (PIBS-C) has the ionizability of taking proton from its acidic interaction partner water, by measuring the pH of the aqueous phases in contact with the nonpolar PIBS-C/hexane solutions. Next, it is shown that a net negative electrophoretic mobility, which is observed when implementing phase analysis light scattering on the nonpolar PIBS-C/hexane solutions, is systematically enhanced upon the deliberate addition of water, suggesting the size asymmetry between (larger) water-swollen micellar anions and relatively dry (smaller) micellar cations. Finally, the measured electric conductivity of the “wet” and “dry” PIBS-C/hexane solutions with and without added water, respectively, is compared and discussed in terms of the amount of water per micelle that is related to the Born radius of the ion.