Wetting and adsorption properties of n-octyl-β-d-glucopyranoside and monorhamnolipid in the system polytetrafluoroethylene–solution–air

Abstract

Abstract The measurements of the contact angle of the aqueous solutions of n -octyl-β- d -glucopyranoside (OGP) and monorhamnolipid (RL) on polytetrafluoroethylene surface (PTFE) as well as the water, diiodomethane and formamide on the PTFE covered by the OGP and RL layer were made at 293 K. On the basis of the obtained contact angle the values of the critical surface tension of the PTFE wetting, adhesion work of the solutions to the PTFE and the adsorption of the OGP and RL at the PTFE–water interface were calculated. The tendency of OGP and RL to adsorb at the PTFE–water interface was considered by determination of the standard Gibbs free energy of adsorption of these surfactants. To determine this energy, a new equation was proposed which was based on the critical micelle concentration of surfactants (CMC), surface tension and contact angle of solution at the CMC. The values of the standard Gibbs free energy of OGP and RL adsorption were compared to those determined by using the Langmuir and Gu and Zhu equations. It was stated that there is the good agreement between these values calculated in different ways. These values are close to those determined for the OGP and RL at the water–air interface.