In this work, the authors investigate the equilibrium swelling of lyogels based on poly(N-isopropylacrylamide) (pNIPAM) in multicomponent solvent systems. The study uses a thermodynamic framework built on Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) and coupled with polymer-network elasticity. Literature parameter sets for the butyl esterification system were assessed and refined, and different network models were compared within a sequential fitting strategy that links solvent, polymer-solution, and gel data.
The results show that the framework can reproduce key swelling trends and supports the transfer of calibrated network parameters between related solvent descriptions. At the same time, the study highlights important limitations. Quantitative fitting of lower critical solution temperature (LCST) behaviour requires a temperature-dependent interaction parameter, finite-extensibility effects are negligible for the investigated systems, and the transferability of fitted interaction parameters to mixed solvents is limited. Overall, the work provides a practical framework for gel equilibrium calculations while emphasising the need for careful interpretation of fitted parameters.
The study is a collaboration between the Institute of Thermal Separation Processes at Hamburg University of Technology and Mercator Fellow Walter G. Chapman from Rice University, carried out within project B01 of the Collaborative Research Centre CRC 1615 (SMART Reactors). It is the second of two connected publications on lyogel equilibria.
Nanning Jaeschke, Walter G. Chapman, Irina Smirnova (2026). Lyogel Equilibria with Helmholtz Equations of State. Part II: Assessment of PC-SAFT Parametrizations and Network Models for pNIPAM Lyogels. Ind. Eng. Chem. Res. 65 (31), 16852-16866.
