Probing Langmuir monolayer self-assembly in condensed and collapsed phases: grazing incidence X-ray diffraction and X-ray standing waves studies

TL;DR

This study reveals a novel corrugated structural state of Ce-induced arachidic acid Langmuir monolayers that persists beyond collapse, confirmed through grazing incidence X-ray diffraction and X-ray standing wave techniques.

Contribution

It uncovers a new monolayer configuration maintained after collapse, characterized by corrugation, expanding understanding of monolayer structural phases under metal ion influence.

Findings

Monolayers remain ordered beyond collapse point.

Corrugated monolayer structure confirmed by diffraction patterns.

Numerical simulations match experimental diffraction data.

Abstract

Ce-induced effects on the self-assembly of arachidic acid Langmuir monolayers was studied in this work. The monolayers were formed on the liquid subphase in the presence of Ce(III) ions. A new type of structural configuration is found for such monolayers, in which the monolayer maintains its structural ordering despite being compressed beyond the collapse point. Instead of forming 3D aggregates as in the typical collapsed state, the monolayer appears to be corrugated. Grazing incidence X-ray diffraction and X-ray standing waves confirm these findings. The diffraction pattern for the monolayer in a new state is represented by the unclosed diffraction rings with maxima near the sample horizon. This diffraction pattern is quantitatively reproduced in the numerical simulations by assuming the corrugated monolayer. The details of the conditions under which these corrugated Langmuir monolayers were observed and the analysis of the diffraction data are described.