Ion Specific Electrolyte Effects on Thin Film Drainage in Nonaqueous Solvents Propylene Carbonate and Formamide

Electrolytes have been found to stabilize thin films in nonaqueous solvents propylene carbonate and formamide, in the absence of surfactant. The thin film balance microinterferometry technique has been used to measure film lifetimes, drainage kinetics, and rupture thicknesses for thin films between air-nonaqueous solution interfaces. Electrolytes that were previously found to inhibit bubble coalescence in bulk bubble column measurements also increase the lifetimes of individual thin films across a similar concentration range (from 0 to 0.3 M). We report that increasing the concentration of inhibiting electrolyte stabilizes the thin liquid film in two ways: the rate of film drainage decreases, and the film reaches a lower thickness before rupturing. In contrast, noninhibiting electrolyte shows little to no effect on film stability. We have here demonstrated that both drainage and rupture processes are affected by the addition of electrolyte and the effect on the thin film is thus ion specific.