Thermotropic Phase Transition in an Adsorbed Melissic Acid Film at the n-Hexane - Water Interface

TL;DR

This study investigates a reversible thermotropic phase transition in an adsorbed melissic acid film at the n-hexane-water interface, revealing crystallization and smectic layering through synchrotron X-ray techniques.

Contribution

It provides new insights into the structural changes during phase transition of melissic acid at the interface, combining X-ray reflectometry and scattering data.

Findings

Interface 'freezing' involves crystallization of the monolayer.

Formation of a planar smectic structure occurs during transition.

The adsorbed film is approximately 300 Å thick with layered substructure.

Abstract

A reversible thermotropic phase transition in an adsorption melissic acid film at the interface between n-hexane and an aqueous solution of potassium hydroxide (pH=10) is investigated by X-ray reflectometry and diffuse scattering using synchrotron radiation. The experimental data indicate that the interface "freezing" transition is accompanied not only by the crystallization of the Gibbs monolayer but also by the formation of a planar smectic structure in the ~300-Angstrom-thick adsorption film; this structure is formed by ~50-Angstrom-thick layers.