Surface Tension, Adsorption, and Wetting Behaviors of Natural Surfactants on a PTFE Surface

The adsorption kinetics and wetting behaviors of three plant-based natural surfactants (Reetha, Shikakai, and Acacia) on the polytetrafluoroethylene (PTFE) surface are reported in this study. Adsorption studies of these surfactants on PTFE surface show the equilibrium adsorption time is approximately 15 min, and Langmuir-type isotherm fits well for all three surfactants. The contact angle measurements show that the value achieved by Reetha and Acacia solutions are close (approximate to 109 degrees), but that is low in the case of Shikakai (98.13 degrees). Although, comparing the adsorption densities of the surfactants at PTFE-water and air-water interfaces, it has been found that adsorption densities at the PTFE-water interface are low for all three surfactants than that of air-water interface. The alcohol-Shikakai mixed solutions show nonideal behavior of surface tension reduction through a strong interaction between alcohol and Shikakai molecules, which in turn, show lower surface tension and contact angle values than that of ideal. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 655-663, 2015