Dilational surface visco-elasticity of CnEOm solutions under dynamic conditions A Physicochemical and engineering aspects

Harmonic surface oscillations of drops are used to study the dilational surface rheology of solutions of the oxyethylated alcohols C10ЕO8, C12ЕO5 and C14ЕO8 at the fixed oscillation frequency of 0.1 Hz for adsorption times between 200 and 5000 s. It was found that at shorter adsorption times the visco-elasticity modulus is lower than its value at longer adsorption times or in the equilibrium state of the adsorption layer at the same surface pressure. This mechanism is explained by the fact that an actual surfactant, characterized by a certain number of EO groups, is in fact a mixture of compounds with a quite wide range of these groups. As molecules with a smaller number of EO groups exhibit a higher visco-elasticity modulus, the changes in the composition of the adsorbed layer during the adsorption lead to the given situation. These considerations are supported by theoretical calculations of the adsorption for mixed surfactants solution.