Electric-field-induced rupture of polymer-stabilized oil films

Water-in-oil emulsions stabilized by polymeric surfactants are robust, but the reasons for their stability are poorly understood. We studied oil films stabilized by a comb-graft copolymer having a poly(siloxane) backbone and poly(ethylene oxide)/poly (propylene oxide) and C-16 grafts (Abil EM-90) wi th a total number-average molecular weight of 62,000. Electric fields impos ed in the aqueous phases on either side of the oil films were used to induc e rapid rupture, and the response of the film was monitored using optical i nterference and electrical conductance measurements. Film thickness values ranged between 30 and 50 nm and rupture at held strength values between 2 x 10(7) and 5 x 10(7) V/m. Unexpectedly, in some cases, stable pores were fo rmed and the films became electrically conductive. Often the pores persiste d for more than 20 min after the voltage had been removed. Since the curren t was independent of film area, very few pores are involved in conduction. This behavior is similar to that found in lipid films; however, the persist ence time is greater for polymer-stabilized films. Because the films are th ick? it is possible that pores are formed by multimolecular-self-assembly a s with pore-forming proteins. polymer purification also influenced film sta bility.