Surface Freezing in Hydrated Alcohol Melts

Surface freezing in hydrated alcohol melts was studied by surface tension and x-ray methods. An ~2.5 swelling of the surface-frozen bilayer is observed at saturated humidity, due to water intercalation into the bilayer. The concomitant upshifts of 2.5 and 3--6 ^∘{}C, observed in the bulk and surface freezing temperatures, respectively, are traced to the surprising increase in hydration upon freezing. For the liquid surface phase, the Gibbs-rule-predicted water depletion at the surface, relative to the bulk, accounts well for the unequal upshifts. It also explains the observed increases in the chain length and temperature ranges over which surface freezing exists.