Wetting of solids by binary surfactant solutions: Synergistic effect

Wetting of glass and polystyrene by aqueous binary surfactant solutions was investigated. The surfactants were cationic - cetyltrimethylammonium bromide (CTAB) and non-ionic - polyoxyethylene-t-octy I phenol (Triton X-100). The mole fraction values of CTAB (alpha) were 0; 0.2; 0.5; 0.8; 1.0. Total surfactant concentrations (c) were varied over the range 10(-8)-10(-2) M. Contact angles were measured by the sessile drop (advancing) and captive bubble (receding) techniques. For glass, the synergistic effect was observed at all a values and over a wide concentration range c = 10(-7)-10(-3) M. For polystyrene, a synergism was observed also at all alpha values in the concentration range c = 10(-4)-10(-3) M corresponding to micellization in these mixtures. The dependence of contact angles on mole fraction of CTAB. alpha correlates well with surface tension isotherms for different a values. The synergistic effect depends on alpha values for wetting of both glass and polystyrene.