Transport and Solvation of Penetrant Molecules in a Thermoresponsive Hydrogel

A wide range of modern soft functional materials, such as nanofilters, nanocarriers, and drug delivery systems, are based on the uptake, release, and diffusive transport of molecules through thermoresponsive polymer architectures. External stimuli, such as changes in temperature, trigger the transition from a swollen into a collapsed state of the polymer, which dramatically alters the thermodynamic and transport properties of penetrant molecules [1,2]. We employ molecular dynamics simulations of a Poly(N-isopropylacrylamide) (PNIPAM) hydrogel with explicit water in its collapsed as well as in the swollen state [3]. The simulations enable us to gain insights into the diffusion and solvation mechanisms of various penetrant molecules in the hydrogel. We find that formations of water pockets, the presence of crosslinkers in the hydrogel, and the polarity of the penetrants play a detrimental role for the diffusion mechanisms and solvation free energies. Finally, we discuss how can the observed phenomena be exploited in hydrogel-based applications of responsive nanoreactors for nanocatalysis [4].

[1] Wu et al. Angew. Chem. 51, 2229 (2012)
[2] Kim et al. Macromolecules 50, 6227 (2017)
[3] Kanduč et al. PCCP 19, 5906 (2017)
[4] Roa et al, ACS Catal. 7, 5604 (2017)