Linear shrinkage of hydrogel coatings exposed to flow: interplay between dissolution of water and advective transport.

Philipp Baumli,Jochen S Gutmann,Lukas Hauer,Emanuela Lorusso,Burkhard Dünweg,Maria D’Acunzi,Azadeh Sharifi Aghili,Doris Vollmer,Katharina I Hegner

doi:10.1039/d1sm01297e

Abstract

We investigate the shrinkage of a surface-grafted water-swollen hydrogel under shear flows of oils by laser scanning confocal microscopy. Interestingly, external shear flows of oil lead to linear dehydration and shrinkage of the hydrogel for all investigated flow conditions irrespective of the chemical nature of the hydrogel. The reason is that the finite solubility of water in oil removes water from the hydrogel continuously by diffusion. The flow advects the water-rich oil, as demonstrated by numerical solutions of the underlying convection-diffusion equation. In line with this hypothesis, shear does not cause gel shrinkage for water-saturated oils or non-solvents. The solubility of water in the oil will tune the dehydration dynamics.

Highlights

We investigate the shrinkage of a surface-grafted water-swollen hydrogel under shear flows of oils by laser scanning confocal microscopy
We find hydrogel shrinkage exclusively caused by the finite solubility of water in the flowing liquid
The purpose of the present paper is to substantiate this picture by reporting our experimental findings obtained by laser scanning confocal microscopy and the corresponding theoretical analysis based on numerical solutions of the convection-diffusion equation that governs the solute dynamics

Summary

Introduction

We investigate the shrinkage of a surface-grafted water-swollen hydrogel under shear flows of oils by laser scanning confocal microscopy. The flow advects the water-rich oil, as demonstrated by numerical solutions of the underlying convection-diffusion equation. In line with this hypothesis, shear does not cause gel shrinkage for water-saturated oils or non-solvents. We find hydrogel shrinkage exclusively caused by the finite solubility of water in the flowing liquid This even happens when the solubility is low, such as in the case of flowing oil. The purpose of the present paper is to substantiate this picture by reporting our experimental findings obtained by laser scanning confocal microscopy and the corresponding theoretical analysis based on numerical solutions of the convection-diffusion equation that governs the solute dynamics

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