THERMAL-EXPANSION COEFFICIENT OF A WATER-SUPPORTED PERFLUORO-N-EICOSANE MONOLAYER

We report the results of grazing incidence X-ray diffraction studies, as a function of temperature, of monolayers of perfluoro-n-eicosane. T he experiments were undertaken to test the suggestion that there is a phase transition in this monolayer between 20 and 25 degrees C, in ana logy with the transition which occurs in Teflon at about the same temp erature. The issue is of importance with respect to determining whethe r description of the properties of a monolayer requires consideration of only the obvious quasi two dimensional character of the monolayer o r requires inclusion of its three dimensional character. Our results d o not support the existence of the suggested transition.