ИСТИНА

Microgel is a unique modifiable polymer system which can be employed as a carrier for various useful functional groups. The attached functional groups can bear charges further employed in the formation of polyelectrolyte complexes; act as antibacterial and antiseptic substance; serve as a conjugation site for a number of target molecules. Microgels enriched with redox-active functional groups (e.g. TEMPO) is a promising catholyte/anolyte material for all-organic redox flow batteries [1]. That allows to have small viscosity at high volume concentration and the micrometer-scale size of the microgels enables application of cheap membranes. Of course, the question of spatial availability of the functional groups is of high importance for practical applications. We performed coarse grained molecular dynamics (MD) simulation in order to investigate spatial distribution and motion of functional groups within the microgel particle. The microgel models used in this work were generated via simulation of the precipitation polymerization process from a dilute solution of initial components, which results in realistic microgel structure [2]. Systems with different structure were obtained by varying the concentration of the crosslinker, reactivity ratios and solvent quality. The mobility of functional groups was assessed through tracing the spatial area swept by the individual bids, particularly its average radius Rsweep. The mobility of functional groups does not correlate directly with the density of a microgel. Higher crosslinker concentration systematically reduces the Rsweep value, i.e. shrinks the volume which a single functional group can diffuse. However, partial collapse does not result in the same effect: some surface-located functional groups even increase its availability area. The simulation results were used to estimate the fraction of distributed functional groups which are available for reactions with large external objects, like electrode surface. Also, the model of functional groups with interchange reactions was studied, simulating electron transfer between redox-active functional groups. A minimum functional group concentration was evaluated to cover the whole microgel volume depending on its structure and solvents quality. Acknowledgement: This work was supported by the Russian Science Foundation, grant 22-13-00115. References: [1] E. Yu. Kozhunova, N. A. Gvozdik, et.al. J. Phys. Chem. Lett. 11 (2020) 10561. [2] V.Y. Rudyak, E.Y. Kozhunova, A. V. Chertovich, Sci. Rep. 9 (2019) 13052.