Melting of 1-Alcohol Mololayers at the Air-Water Interface. I. X-Ray Reflectivity Investigations

The melting of I-alcohol monolayers adsorbed at the air-water interface has been studied using X-ray reflectivity. This technique allows for an accurate determination of the thickness and the density of the monolayer. The reflectivity, both in specular and non-specular directions, over a large temperature range of different chain lengths (from Cio to C16) have been interpreted using a model taking into account the scattering from thermally induced capillarywave fluctuations and the instrumental resolution. The density and the thickness of the aliphatic layer exhibit a clear discontinuity at the solid-liquid transition. Large changes with temperature in the packing of the monolayer are observed in both the solid and the liquid phase. In the crystal phase, the fitted thicknesses are lower than all-trans molecular chain lengths. In the liquid phase, the density remains 10$l larger than in bulk liquid phases. @ Les Editions de Physique 1995 608 JOURNAL DE PHYSIQUE II N°4