Jeremy J. Porter, Jane K. Klassen, and Gilbert M. Nathanson

Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706

Received May 10, 1996. In Final Form: July 30, 1996

Perfluorinated polyether(PFPE) films spread spontaneously on concentrated sulfuric acid to form insoluble thin films that act as diffusion barriers to water vapor condensation. At acid concentrations between 89 and 95 wt %, the average film resistivity for water vapor is 8.3 ± 1.0 s/cm per um thickness of PFPE. This resistivity corresponds to a diffusion coefficient for water in PFPE of -6 x 10-1 CM2/S. Thus, a several micrometer thick PFPE film resists water condensation with an efficiency_greater than the evaporation resistance of many long chain alcohol monolayers on water. Below ~90 wt% sulfuric acid, thin indentations appear in the PFPE film and the resistivity drops to -4 (s/cm)/um near 84 wt % acid.