Compression of colloidal monolayers at liquid interfaces: in situ vs. ex situ investigation

TL;DR

This study compares in situ and ex situ methods for analyzing colloidal monolayers at liquid interfaces, revealing that traditional transfer techniques can significantly alter the monolayer's microstructure, impacting the interpretation of experimental results.

Contribution

The paper introduces an in situ light scattering setup coupled with a Langmuir trough to directly monitor colloidal monolayers during compression, challenging assumptions about structural preservation in ex situ analyses.

Findings

Ex situ transfer can alter monolayer microstructure.

In situ monitoring provides more accurate structural information.

Langmuir-Blodgett deposition may change colloidal arrangements.

Abstract

The assembly of colloidal particles at liquid/liquid or air/liquid interfaces is a versatile procedure to create microstructured monolayers and study their behavior under compression. When combined with soft and deformable particles such as microgels, compression is used to tune not only the interparticle distance but also the underlying microstructure of the monolayer. So far, the great majority of studies on microgel-laden interfaces is conducted ex situ after transfer to solid substrates, for example, via Langmuir-Blodgett deposition. This type of analysis relies on the stringent assumption that the microstructure is conserved during transfer and subsequent drying. In this work, we couple a Langmuir trough to a custom-built small-angle light scattering setup to monitor colloidal monolayers in situ during compression. By comparing the results with ex situ and in situ microscopy measurements, we conclude that Langmuir-Blodgett deposition can alter the structural properties of the colloidal monolayers significantly.