Temperature-Dependent Swelling Kinetics and Thermodynamic Parameters of a Xanthan/Polyacrylamide-Based Hydrogel in Different Media

Abstract

This study addresses this gap by systematically evaluating temperature and contact time, providing insights essential for optimizing hydrogel performance in applications such as controlled release and water shut-off. In this study, a hydrogel with high-swelling capacity (max. 241 g/g) was synthesized via alkaline crosslinking of a homogeneous mixture of the biopolymer xanthan and polyacrylamide. The solution, containing a low concentration of reagents, was converted into a gel-forming material within 4–6 h at 40 °C through reaction with glutaraldehyde. The structure of the crosslinked macromolecular network was characterized by FTIR spectroscopy, revealing that crosslinking predominantly occurs through the formation of bridges by glutaraldehyde between the -NH₂ groups of polyacrylamides and the -OH groups of xanthan. The swelling behavior of the hydrogel was investigated as a function of time in different pH media, as well as in NaCl, CaCl₂, and AlCl₃ solutions. To elucidate the swelling mechanisms, first- and second-order kinetic models, as well as the Ritger-Peppas, Weibull, and Peppas-Sahlin models, were applied. It was determined that the swelling process follows a non-Fickian diffusion mechanism at lower temperatures and in physiological solutions. The observed increase in swelling with temperature can be attributed mainly to the enhanced mobility of polymer chains, accelerated diffusion of water molecules into the polymer network, and increased accessibility of hydrophilic functional groups to water at elevated temperatures. The thermodynamic parameters of swelling in water and physiological solutions were evaluated, and the activation energy was calculated. The Gibbs free energy of swelling in water within the temperature range of 293–343 K was found to be ΔG° = -18.9 to (-36.1) kJ/mol, while in physiological solution it ranged from ΔG° = -8.04 to (-10.11) kJ/mol. The activation energy of swelling was determined to be E_a=17.42 kJ/mol in water and E_a=8.91 kJ/mol in physiological solution. The sensitivity of the hydrogel’s structure to temperature allows for its potential application in drug delivery and controlled release systems, as well as eco-friendly an in-situ gelation system for water shut-off operation.