Swelling Behavior of a Crosslinked pHEMA Hydrogel in pH and Salt Environments

The swelling behavior of non‐ionic crosslinked poly hydroxyethyl methacrylate (pHEMA) is investigated in alkaline, acidic, and electrolyte solutions. The swelling behavior is affected by the crosslinker concentration, pH, and swelling time. An intermediate crosslinker concentration requires 24 h to reach equilibrium swelling in which the final swelling extent decreases with increasing pH. For swelling times of 90 min with lower and intermediate crosslinker concentrations, the swelling first increases followed by a decrease with increasing pH. In electrolyte solutions of monovalent cations, swelling follows the direct Hoffmeister series, whereas in electrolyte solutions of divalent cations, the swelling follows the indirect Hoffmeister series. The precise swelling mechanisms are dictated by specific Ion‐pHEMA‐water interactions. This work shows that the swelling behavior of pHEMA is dictated by the precise swelling conditions and environment. Therefore, careful analysis of the relevant processes is essential to accurately characterize the swelling behavior of non‐ionic hydrogels, which determines their functionality and applicability.