Cross-linked hydrophilic polymers: universal sensors for analyzing solutions containing polar organic compounds
This study presents a quantitative assessment of cross-linked polyvinyl alcohol (PVA) granules as sensing elements for detecting aliphatic carboxylic acids and their sodium salts in aqueous solutions. Swelling kinetics were measured across solute concentrations ranging from 0.2 N to 1.0 N, with the granule radius varying between 0.31- and 0.43-mm. Results indicated that both carbon chain length and the presence of additional carboxyl groups exert a pronounced effect on the equilibrium swelling degree, thereby highlighting the interplay between hydrophobic interactions and hydrogen-bond formation. To interpret these observations, a heterophase physicomathematical model was employed, yielding three main kinetic coefficients (K1, K2, and K3) that capture solvent flux, polymer network elasticity, and solute transport. The model fits exhibited root-mean-square deviations below 1 %, attesting to its reliability in describing complex swelling - deswelling processes. Additionally, three-dimensional kinetic surfaces were constructed to illustrate how swelling evolves over time and concentration, revealing that initial swelling curves can serve as a rapid indicator of solute concentration. By leveraging the reversible nature of polymer swelling, this method offers a non-invasive, cost-effective approach suitable for monitoring organic acids in diverse fields such as environmental analysis, pharmaceutical processes, and chemical engineering.
