# Adsorption of Surfactants and Polymers to Biomimetic Hair Model Surfaces

## TL;DR

This study explores how eco-friendly ingredients in shampoos interact with different hair surfaces using advanced techniques to improve product sustainability and performance.

## Contribution

The novelty lies in using neutron reflectometry and AFM to study adsorption on biomimetic hair surfaces with varying damage levels.

## Key findings

- The methyl branch of 18-MEA influences surface interactions with adsorbates.
- Polymer adsorption is enhanced in surfactant/polyelectrolyte mixtures.
- Partially damaged hair surfaces show distinct adsorption behaviors on hydrophobic and hydrophilic patches.

## Abstract

Improving the sustainability of cosmetic products while
maintaining
a good performance requires a deeper understanding on the way that
new eco-respectful ingredients interact with hair or skin. In the
case of shampoos, the surface science is dominated by the diverse
changes on the hair fiber due to both chemical and physical damages
that particularly affect physicochemical properties such as hydrophobicity.
A native, undamaged fiber is covered with a monolayer of lipids, mainly
18-methyleicosanoic acid (18-MEA), while a highly damaged hair surface,
having completely lost the protective lipids, is hydrophilic and negatively
charged. Intermediate states exist, where there is a partial loss
of 18-MEA (“partially damaged hair”). Here, four model
surfaces have been produced, to mimic different types of hair surfaces.
Their interaction with selected surfactants and polyelectrolytes (natural
and synthetic) has been studied by neutron reflectometry (NR). NR
can reveal hierarchical adsorption from mixtures thanks to the scattering
contrast between deuterated and hydrogenous molecules. Atomic force
microscopy (AFM) measurements complement the study by adding information
about the in-plane structure of adsorbed species. The presence of
the methyl branch of 18-MEA is found to affect the interaction of
the surface with adsorbates. For surfactant/polyelectrolyte mixtures,
for example, the adsorption of polymer is enhanced. Of particular
interest are the results on the partially damaged hair model, as it
manifests patches of hydrophobic and hydrophilic moieties; it is possible
to separately observe the different adsorption behaviors to the different
sites in a single experiment.