Crystalline bilayers on the surface of molten alcohol

Surface freezing is discovered in normal alcohol melts and studied using surface X-ray scattering techniques. A single crystalline bilayer is formed on the surface, at temperatures up to 1 °C above the bulk freezing temperature. The single bilayer persists down to bulk freezing. It is hexagonally packed, and the molecules are vertical for short chains and tilted for long ones. The two layers comprising the bilayer are shifted relatively in the next-nearest-neighbor direction. The structural details of the layer, its range of existence in temperature and chain length, its relation to Langmuir films and to the recently discovered surface crystallization in alkane melts are discussed.