ELLIPSOMETRY STUDY OF 2D CRYSTALLIZATION OF 1-ALCOHOL MONOLAYERS AT THE WATER-SURFACE

We investigate monolayers of 1-alcohols (C8 to C14) obtained by placing an excess of material on top of a clean water surface. The excess is collected in a lens which constitutes a reservoir of molecules for the monolayer. We observe a first-order transition (2D crystallization) with temperature. Ellipsometry measurements show a narrow transition in temperature with no measurable hysteresis corresponding to a jump of the monolayer thickness. For each sample, simultaneous surface tension measurements show a break of slope at the same transition temperature. Both below and above the transition we observe large positive coefficients for the temperature variation of the surface tension.