# Elucidating and Mitigating Instabilities of Poly(vinyl alcohol) Thin Films in Aqueous Environments

## TL;DR

This study investigates how poly(vinyl alcohol) thin films break down in water and how to stabilize them using chemical treatments.

## Contribution

A new 'landmarking and overlaying' method is introduced to quantify polymer rearrangement, and in situ cross-linking is shown to mitigate PVOH instability.

## Key findings

- PVOH88%H shows faster desorption–readsorption kinetics and more rearrangement upon water exposure.
- In situ cross-linking with glutaraldehyde eradicates dewetting of PVOH on PDMS substrates.
- Ex situ cross-linking with succinyl chloride preserves fractal structures upon water exposure.

## Abstract

In this study, 88% and 99% hydrolyzed poly­(vinyl alcohol)
(PVOH88%H and PVOH99%H, respectively) polymers
were statically
adsorbed and spin coated from an aqueous solution onto high molecular
weight (HMW) polydimethylsiloxane (PDMS) substrates. The resulting
PVOH thin films are unstable and rupture into fractal structures in
a diffusion-limited aggregation fashion upon drying. The dynamics
of these fractal thin films upon immersion in water and upon exposure
to a single water droplet were closely examined. A newly developed
“landmarking and overlaying” method was used to quantify
the extent of polymer rearrangement under these conditions. Overall,
both types of PVOH films exhibit instability in aqueous environments;
however, PVOH88%H has faster desorption–readsorption
kinetics at the substrate–solution and substrate–solution–air
interfaces, resulting in more significant rearrangements upon water
exposure. Ex situ cross-linking reactions using succinyl
chloride in the vapor phase were carried out on the PVOH fractal thin
films. Under the optimal reaction conditions, the PVOH fractal structures
were entirely preserved upon water exposure. In situ cross-linking reactions using glutaraldehyde were performed on the
PVOH thin films in contact with solution. Microscopic dewetting of
PVOH on HMW PDMS and nanoscopic dewetting of PVOH on intermediate
MW PDMS were eradicated. The in situ cross-linking
results provide convincing evidence that PVOH dewetting takes place
during the drying process and can be mitigated.