Excess adsorption on hydrophobic and hydrophilic solid-liquid interfaces.Positive excess adsorption of non-ionic surfactant.Part 1

摘要

The extent of adsorption (GAMMA_2~1) of non-ionic surfactant Tween-20 onto hydrophilic alumina and silica and hydrophobic charcoal surfaces has been measured as a function of surfactant concentration (X_2) in mole fraction unit at different temperatures.For each isotherm,GAMMA_2~1 at low range of X_2 increases with increase in surfactant concentration.But,it reaches maximum (GAMMA_2~m) when X_2 reaches a critical value X_2~m .With increase in temperature,GAMMA_2~m increases for charcoal and silica surfaces while it decreases for alumina surface.At 40 deg C,GAMMA_2~1 at charcoal surface begins to decrease when X_2 exceeds GAMMA_2~m.At 30 deg C for charcoal surface,GAMMA_2~1 increases sharply with increase in X_2 without reaching any limiting value due to the multilayer adsorption of Tween-20.Similar formation of multilayers is also observed at alumina-water interface when the surface coverage is significantly low.Fomation of multilayers of Tween-20 molecules on the surface of silica is not observed even when X_2 is relatively high.Using the integrated form of the Gibbs adsorption equation,the standard free energy change DELTAG~0 deg for the adsorption of non-ionic surfactant per square meter of powdered surface due to the change of the bulk activity of Tween-20 from zero to unity has been evaluated and critically examined.