THE INFLUENCE OF AQUEOUS METHANOL FILM ON THE WETTABILITY OF POLYTETRAFLUOROETHYLENE

Contact angles were measured for polytetrafluoroethylene (PTFE) wetted with aqueous methanol solutions-water drop or diiodomethane drop-air systems as a function of the holding time of the PTFE plate in the measuring chamber filled with a mixture of molecular sieves (4 A ̊ + 5 A ̊); a theoretical analysis of the equilibrium state of these systems was also made. Using published data, the components of the surface free energy of PTFE for various degrees of the coverage of its surface by water and methanol film were calculated. The contact angles for water and diiodomethane drops settled on PTFE/mixed film (water + methanol) were calculated and compared with the measured values. On the basis of these measurements and calculations, it was found that the contact angle for a water drop depends on the degree of the coverage of the PTFE surface with molecules of methanol, but the contact angle for a diiodomethane drop depends on the degree of a coverage of the PTFE surface with water and methanol molecules. It was shown that the measured contact angles for the studied systems were in the range of the calculated values. © 1990.