  Stimuli-responsive lyogels are considered to be smart materials due to their
capability of undergoing significant macroscopic changes in response to
external triggers. Due to their versatile and unique properties, smart lyogels
exhibit great potential in various applications such as drug delivery or
actuation processes. While Poly-N-isopropylacrylamide (pNIPAM) is widely known
as a thermo-responsive material, it also shows significant solvent-responsive
swelling behavior. As polar solvents induce strong swelling due to hydrogen
bonding with the amide group, nonpolar solvents lead to significant shrinkage
of the lyogels. The aim of this study is to investigate and to model this
behavior for future application in chemical or biochemical reactors. As a
current area of research, incorporating smart hydrogel technology into
(bio-)chemical reactors facilitates the development of smart reactor systems.
Applying thermodynamic modelling with the gE model COSMO-RS on the monomer or
oligomers of pNIPAM, the correlation between solvent-polymer interactions and
the degree of swelling can be observed. pNIPAM derivatives exhibit low
infinitive dilution activity coefficients (IDACs) in polar solvents with large
degrees of swelling, while displaying an increase of IDACs in nonpolar
solvents. Hydrogen bonds dominate the swelling behavior of lyogels not only in
pure solvents but also in mixtures of solvents with varying polarity. Even in
mixtures containing high amounts of nonpolar solvents, large degrees of
swelling were observed due to the uptake of the polar solvent in the lyogel
matrix. This effect can be observed in binary solvent mixtures but also in
representative mixtures along an esterification reaction with varying
carboxylic chain length of alcohol and carboxylic acids.
