Exploring pNIPAM Lyogels: Experimental Study on Swelling Equilibria in Various Organic Solvents and Mixtures, Supported by COSMO-RS Analysis

The study focuses on pNIPAM lyogels, which are described as smart materials because they can undergo large macroscopic changes when exposed to external triggers. Although pNIPAM is known for thermoresponsive behavior, the authors emphasize that it also responds strongly to solvents through swelling and shrinkage. They report that polar solvents tend to swell the lyogels due to hydrogen bonding with the amide groups, while nonpolar solvents cause shrinkage. The work also examines solvent mixtures, showing that even when nonpolar solvents are present in high amounts, the lyogel can still swell substantially because polar solvent can be taken up into the matrix. To support and model these observations, the authors apply thermodynamic modeling using the gE model COSMO-RS to pNIPAM monomers/oligomers, relating solvent–polymer interaction strength to the degree of swelling. They further discuss hydrogen bonding as a dominant factor in both pure solvents and mixtures, including representative mixtures along an esterification reaction with varying alcohol and carboxylic acid chain lengths.