Effects of surfactant on capillary evaporation process with thick films

Capillary evaporation has been widely applied in petroleum industries, chemical process industries and soil science, while surfactants are usually existed in the working liquid for these applications. In this paper, we investigated effects of surfactant on capillary evaporation with thick films from aspects of evaporation rates, morphologies of meniscus and contact angles between the capillary and the working liquid. The results show that, different from that in an unconfined space, in capillary evaporation the evaporation rate decreased with the increase of surfactant concentrations. This discrepancy is attributed to the decisive role of surfactant concentration in the kinetics of capillary evaporation and the deterministic role of evaporating area in the unconfined space. Although the surfactant can alter the surface tension of vapor/liquid, but cannot affect the meniscus shape in the capillary evaporation process with thick films. Moreover, the contact angle between the capillary and the working liquid were not influenced by the addition of surfactant.