Effects of surfactants on the rate of thinning of the dimple between a horizontal glass plate and an air bubble in water

Abstract

We in investigated the effects of sodium dodecyl sulfate (SDS) on the rate of thinning of the dimple formed between an air bubble and a glass plate horizontally immersed in water. The activation energy of thinning of the dimple increases with increasing concentration of SDS and flattens in the saturated adsorption region. The increment may be regarded as the activation energy of the surface flow. Addition of dodecanol to the saturated adsorption surface of SDS results in further increase in activation energy. The Arrhenius equation does not hold for these cases but should be transformed to k = A′ exp(−ΔH ‡/RT + ΔS ‡/R , where ΔH ‡ and ΔS ‡ are the activation enthalpy and entropy of thinning of the dimple, respectively, and the latter was estimated from the data for dodecanol. The electrical force acting between glass and bubble surfaces is rather smaller in SDS solutions in potassium chloride solutions because of the compensation of the ionic strength effect by the surface charge effect. It may be conclude that ΔH ‡ would be contributed by the surface shear viscosity but not by the surface area viscosity, because a nonionic surfactant, heptaethylene glycol dodecyl, has no effect on ΔH ‡ .