Structure and Dynamics of Temperature-Responsive Microgels and Hydrogels by NMR Spectroscopy, Relaxometry, and Diffusometry

Abstract

Stimuli-responsive polymer networks like microgels and hydrogels possess a variety of properties that need to be analyzed for their rational design and successful application in the targeted field of interest. Nanoscale characterization of gels can be achieved by highly selective and sensitive techniques including high-resolution NMR spectroscopy, relaxometry, and diffusometry. This review is focusing on recent results using 1H and 13C 1D and 2D NMR techniques, which give chemically site-selective information about the polymer network revealing the interplay between structure and dynamics of polymer networks at the nanoscale level. By that, NMR can allow to obtain information about i) internal structure, ii) stimuli-induced phase transition, iii) mesh size, and iv) aggregation of microgels and hydrogels. The rational design of responsive microgels and hydrogels with application in drug delivery, cell carrier systems, catalysis, actuators, and as antibacterial agent can be made, if crucial polymer network properties can be correlated with cross-linking density, type of cross-link interactions, electrical charges, hydrophobic nano-structuring, and dispersion concentration.