Effect of temperature on the wettability of low-energy surfaces

Abstract

Advancing and receding spreading coefficients of pure water and of solutions of tetradecyltrimethylammonium bromide (T.T.A.B.) wetting a paraffin wax surface have been measured over the temperature range 20° to 45°C. The surface tensions of the solutions of T.T.A.B. were also measured over the same temperature range. Special care was taken in preparing uniform wax surfaces so that wetting hysteresis was reduced to a minimum level. Even so, advancing spreading coefficients were invariably lower (i.e., a larger negative value) than receding values. At the liquid-air interface T.T.A.B. adsorbed more readily at low temperatures than at high. The decrease of surface tension with temperature at low concentrations of T.T.A.B. is entirely due to the effect of water in the surface. At high concentrations of T.T.A.B. where the surface was nearly saturated the surface tension remained constant with temperature and the process of surface formation accordingly became isentropic. The spreading coefficient of a solution of given concentration was added to twice its equilibrium value of surface tension to give the work of adhesion. This was then plotted as a function of temperature. The work of adhesion of pure water on wax increased with temperature for advancing conditions only. For receding conditions the work of adhesion decreased with temperature. Addition of T.T.A.B. to the advancing spreading liquid had the effect of increasing the work of adhesion by about 10 ergs/cm 2 but the amount did not vary significantly with temperature. Receding solutions of T.T.A.B., as well as pure water, prossessed works of adhesion large than those of advancing solutions. The work of adhesion for receding conditions decreased with temperature. Hysteresis and its temperature coefficient is explained as being due to hydrophilic patches on the wax surface adding to the work of adhesion under receding conditions but not under advancing conditions. The effect of T.T.A.B. at the solid-liquid interface increases the work of adhesion by replacing water with monolayer that attracts was more strongly. The behavior of this system is discussed in relation to other work.