THE EVAPORATION RESISTANCE OF OCTADECANOL MONOLAYERS AS A FUNCTION OF TEMPERATURE

Surface pressure-area isotherms and resistances to water evaporation have been measured on octadecanol monolayers at temperatures from 1 to 48°C. The data are used to examine three theories of monolayer permeation: the energy barrier theory, the density fluctuation theory, and the accessible area theory. Each theory is in reasonable accord with the experimental results: the Arrhenius plots are linear over the entire temperature range; experimental values of the entropy of expansion or spreading yield, through the density fluctuation theory, reasonable values for the evaporation resistance; and the change in evaporation resistance with temperature can be attributed to the expansion of the monolayer, as suggested by the accessible area theory. Thus there is no evidence favoring one theory over another. The evaporation resistance data show no perturbations which could be attributed to changes in the structure of vicinal water or to the solid-superliquid phase transition. © 1990.