# Humidity-Induced Structural Transformation in Self-Organized Polymer–Surfactant Multilayer Nanofilms

## TL;DR

This study explores how humidity changes the structure of polymer-surfactant nanofilms, revealing a mechanism that could be used to create smart antimicrobial coatings.

## Contribution

The study reveals a humidity-induced structural transformation mechanism in polymer–surfactant nanofilms, enabling potential applications in controlled release coatings.

## Key findings

- Exposure to humidity causes a reorganization of the film into a vertically stratified multilayer structure.
- Surfactant-rich domains form with increased humidity, indicating high surfactant mobility in the polymer matrix.
- Surfactant nanocrystals diffuse upon humidity exposure, forming reservoirs for potential controlled release.

## Abstract

We have investigated the humidity-responsive structure
of polymer–surfactant
multilayer nanofilms composed of a hydrophilic maleic acid polymer
and an amphoteric amine oxide surfactant (C12-AO). Neutron reflectometry
(NR) revealed the presence of a smooth thin film comprising several
surfactant bilayers intercalated with the polymer. Upon exposure to
increased humidity, the nanostructured film reorganized into a vertically
stratified multilayer structure with polymer chains located in the
vicinity of hydrated surfactant headgroups, with further humidity
increase leading to the formation of surfactant-rich domains, indicating
a high mobility of the surfactant molecules in the polymer matrix.
Off-specular neutron reflectometry and grazing-incidence X-ray scattering
revealed the presence of surfactant nanocrystals in the as-prepared
film, which diffused to form surfactant-rich domains upon exposure
to humidity, thus providing a reservoir of surfactants. These findings
help elucidate a mechanism of structural transformation in dried polymer–surfactant
films, thus suggesting an avenue for engineering an antimicrobial
coating with longevity and a humidity-activated release of active
molecules using two-dimensional confinement effects.