Tailoring the viscoelasticity of polymer gels of gluten proteins through solvent quality

TL;DR

This study explores how solvent quality affects the viscoelastic properties of gluten protein gels, revealing a superposition principle and a solvent-dependent transition in molecular interactions that can be used to tailor gelation.

Contribution

It demonstrates a universal superposition principle for gluten gels in water-ethanol mixtures and links molecular interactions to macroscopic viscoelastic properties.

Findings

Gels exhibit a time/solvent composition superposition principle.

Viscoelastic parameters span several orders of magnitude with solvent change.

Molecular interactions transition from intra- to interchain with increased ethanol.

Abstract

We investigate the linear viscoelasticity of polymer gels produced by the dispersion of gluten proteins in water:ethanol binary mixtures with various ethanol contents, from pure water to 60% v/v ethanol. We show that the complex viscoelasticity of the gels exhibits a time/solvent composition superposition principle, demonstrating the self-similarity of the gels produced in different binary solvents. All gels can be regarded as near critical gels with characteristic rheological parameters, elastic plateau and characteristic relaxation time, which are related one to another, as a consequence of self-similarity, and span several orders of magnitude when changing the solvent composition. Thanks to calorimetry and neutron scattering experiments, we evidencea co-solvency effect with a better solvation of the complex polymer-like chains of the gluten proteins as the amount of ethanol increases. Overall the gel viscoelasticity can be accounted for by a unique characteristic length characterizing the crosslink density of the supramolecular network, which is solvent composition-dependent. On a molecular level, these findings could be interpreted as a transition of the supramolecular interactions, mainly H-bonds, from intra- to interchains, which would be facilitated by the disruption of hydrophobic interactions by ethanol molecules. This work provides new insight for tailoring the gelation process of complex polymer gels.