A study of the solution, interfacial and wetting properties of silicone surfactants

Abstract

This work reports an investigation of the solution, interfacial and special wetting properties of a group of three silicone surfactants using surface tension, wetting, adsorption, fluorescence and fluorescence decay techniques. Aqueous solutions of two of these surfactants exhibit a c.m.c. type break in the surface tension versus concentration plot. Fluorescence and turbidity measurements show that for one (SS1) the break corresponds to the formation of well dispersed droplets rather than micelles. A second surfactant, SS2, forms micelles in solution of aggregation number around 30 which is significantly lower than that for conventional surfactant micelles. SS1, with a compact hydrophobic group and a long polyether tail, reduces the surface tension of water to 20.5 mN m −1 and exhibits a unique ability to wet low energy surfaces such as polyethylene. Interestingly, fluorocarbon surfactants which can lower the surface tension of water even further do not wet polyethylene as efficiently. The special wetting properties of SS1 are attributed to a variety of factors, i.e., its unique structure, ability to lower the liquid-air surface tension to extremely low values, fast kinetics of adsorption at the liquid-air and solid-liquid interfaces, high affinity of the surfactant for low energy surfaces, and favorable orientation and structure of its adsorbed molecules.