Significance of surface excess concentration in the kinetics of surfactant-induced pore wetting in membrane distillation

Failure of membrane distillation (MD) due to pore wetting by amphiphilic molecules has recently received growing interests because it is a critical challenge to overcome for MD to be applicable for treating unconventional feed water. Recent MD studies using feed solutions containing surfactants have elucidated fundamental mechanism of wetting and generated practical solutions for wetting mitigation. However, what remains unclear is the impact of surfactant species on pore wetting kinetics. Based on a recently developed kinetic model for surfactant-induced pore wetting in MD, we hypothesize that the surface excess concentration of a surfactant is the most important surfactant property in affecting the pore wetting kinetics. In this study, we performed controlled MD wetting experiments using seven different types of surfactants and measured their respective breakthrough time as a quantitative metric for wetting kinetics. Our experiments reveal a good linear correlation between the surface excess concentration and breakthrough time for most but one tested surfactant. When surface excess concentration and diffusion coefficient are both considered, the model-simulated breakthrough time matches the experimentally measurement remarkably well for all tested surfactants.