Mutual influence of ethanol and surfactin on their wetting and adhesion properties

Abstract

The measurements of the contact angle of aqueous solution of ethanol and surfactin mixture in the whole range of ethanol concentration on PTFE, PMMA and quartz were made at changing ethanol concentration and constant of surfactin and vice versa. Based on the obtained results, the Young-Dupre and van Oss et al. equations, the intermolecular interactions parameter between the solution and solid phases was determined and used to explain the possibility to form the ethanol and surfactin mixed layer beyond the solution drop settled on the PMMA and/or quartz surface. This layer pressure and that at the PMMA-solution, the quartz-solution interface was determined using the Young-Dupre and van Oss et al. equations and applied for the ethanol and surfactin Frumkin isotherm adsorption determination. The Gibbs adsorption isotherm was also determined. The ethanol and surfactin Gibbs and Frumkin isotherms at the solid-solution, solid-air interfaces were compared to those at the solution-air one. From these isotherms of surfactin and ethanol adsorption at three interfaces, the slope of the linear dependence between the adhesion and surface tension was explained. The Gibbs isotherm was applied for determination of the Gibbs standard free energy of ethanol and surfactin adsorption at the solid-air and solid-water interfaces.