Rheological properties of acid-induced carboxymethylcellulose hydrogels

TL;DR

This study investigates the rheological behavior of acid-induced carboxymethylcellulose hydrogels, revealing their viscoelastic properties, temperature dependence, and reversible yielding, providing insights into their physical gel nature and pH effects.

Contribution

It provides a detailed rheological characterization of acid-induced CMC hydrogels, including linear and non-linear properties, and models their behavior using fractional models and Arrhenius-like temperature dependence.

Findings

CMC gels are reversible and exhibit a yielding transition.

Viscoelastic spectra follow fractional models with temperature-dependent shift factors.

Activation energies suggest hydrophobic interactions govern gel formation.

Abstract

Cellulose ethers represent a class of water-soluble polymers widely utilized across diverse sectors, spanning from healthcare to the construction industry. This experimental study specifically delves into aqueous suspensions of carboxymethylcellulose (CMC), a polymer that undergoes gel formation in acidic environments due to attractive interactions between hydrophobic patches along its molecular chain. We use rheometry to determine the linear viscoelastic properties of both CMC suspensions and acid-induced gels at various temperatures. Then, applying the time-temperature superposition principle, we construct master curves for the viscoelastic spectra, effectively described by fractional models. The horizontal shift factors exhibit an Arrhenius-like temperature dependence, allowing us to extract activation energies compatible with hydrophobic interactions. Furthermore, we show that acid-induced CMC gels are physical gels that display a reversible yielding transition under external shear. In particular, we discuss the influence of pH on the non-linear viscoelastic response under large-amplitude oscillatory shear. Overall, our results offer a comprehensive description of the linear and non-linear rheological properties of a compelling case of physical hydrogel involving hydrophobic interactions.