MOLECULAR LAYERING IN A LIQUID ADSORBED FILM AT ROOM-TEMPERATURE

We present the first observation of structural effects in a film adsorbed from vapor at room temperature. A new ellipsometric technique has enabled us to identify steps in the adsorption isotherm of the nonpolar liquid octamethylcyclotetrasiloxane on molecularly smooth mica. The transition from one layer to two layers of adsorbed molecules at a relative vapor pressure of 0.8 is particularly distinct. This layering transition shifts toward higher vapor pressure with decreasing temperature but no qualitative change is found on passing through the triple point of the bulk liquid. Such layering phenomena in adsorbed films have previously only been detected in films of inert and other simple gases at low temperatures.