Effect of ethanol on wetting and adhesion properties of rhamnolipid

Abstract

The wetting and adhesion properties of the surfactants and biosurfactants play a very important role in the processes occurring in practice. These properties can be changed by the addition to the aqueous solution of the surfactants and biosurfactants different kinds of the substances influencing the structure of water and the hydration of the head and tail of the surfactants molecules. Therefore, we studied effect of the ethanol on the wetting and adhesion properties of rhamnolipid by the measurements of the contact angle of the aqueous solution of rhamnolipid in the presence of ethanol on the polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA) and quartz surface. The obtained results of the contact angle were analyzed in the light of the surface tension components of the solids, water, ethanol as well as the head and tail of the rhamnolipid surface tension. Based on these analyses the adsorption of the ethanol and rhamnolipid at the solid-solution, the dependence between adhesion and surface tension, the dependence between the adhesion work of the solution to the solid surfaces and solution surface tension as well as the critical surface tension of solid wetting were considered. The critical surface tension was compared to the surface tension of the solid. From above mentioned consideration, it appeared, among other things, that on the basis of the PTFE-aqueous solution of ethanol (ET) and PTFE-aqueous solution of rhamnolipid (RL) interface tension, it is possible to predict the contribution of ET and RL adsorption at the PTFE-solution of RL and ET mixture. It also appeared that it is possible to determine the Gibbs standard free energy of ET and RL adsorption at the solid-air and solid-solution interfaces, by using the Gibbs excess concentration of ET and RL at these interfaces determined on the basis of contact angle in Langmuir equation modified by de Boer. • Replacement of RL by ET molecules in interfaces layer can cause contact angle increase. • Above ET CAC contact angle depends practically on its adsorption at interfaces but not RL. • Parameter changes linearly as a function of logarithm from sum of and but not • Solution of ET and RL mixture spreads complete over PMMA and quartz at C of ET higher than its CAC. • For PMMA and quartz there is linear dependence between adhesion work and