Surface diffraction studies of 2D crystals of short fatty alcohols at the air-water interface

Abstract

Using X ray surface diffraction we have investigated crystalline monolayers of short alcohols (1-decanol to 1-tetradecanol) at the air-water interface in the vicinity of the first order transition corresponding to 2D melting (T_m(2D)). The diffraction patterns in the solid phase are in agreement with a 2D hexagonal close-packing. The lattice parameter value is 5.00 Å just below T_m(2D) and amounts 4.90 Å at T_m(2D)-20 K. The resolution limited Bragg peaks indicate a large crystalline coherence length. At the approach of the 2D melting point, the observed increase of the Debye Waller factor is attributed to critical fluctuations.