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 1 H and 13 C 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.

The Influence of Lyophilization Pretreatment and Whey Content on Whey and Gelatin-Based Hydrogels

“…The integral area of these peaks diminishes as the T 2 values increase, indicating that the smaller parts of the crosslinked hydrogel exhibit increased mobility at a molecular (polymer chain network) level. Nevertheless, among all the 1 H NMR relaxometry studies of various types of hydrogels (microgels) [38][39][40], these samples present the most reduced mobility polymer network.…”

Superabsorbent polymers in soil: The new microplastics?

“…While rheological measurements provide information about the mechanical behavior of samples, nuclear magnetic resonance (NMR) techniques, namely 13 C-and solid-state NMR spectroscopy, diffusion-ordered spectroscopy and 1 H-NMR relaxometry, provide information on the chemical composition, molecular structure, dynamics, solvent interactions and conformational changes of samples (Vandersypen and Chuang, 2005;Brax et al, 2017;El Nokab et al, 2022;Plante et al, 2023). 1 H-NMR relaxometry uses nuclear spin relaxation times, two-dimensional correlation spectra and water diffusivity to measure structural features and dynamics between sample structures and water molecules in situ (Demco and Pich, 2023). It is commonly used for hydrogels and soil to assess polymer-water interactions and water molecule mobility and binding (Romero-Zeron et al, 2004;Buchmann and Schaumann, 2017;Brax et al, 2018;Arens et al, 2019;Buchmann et al, 2020).…”

Investigation of morphology and volume phase transition of supramacromolecular microgels by NMR spectroscopy and quartz crystal microbalance

“…In order to rationally design microgels for a broad range of applications, an understanding of their morphology, volume phase transition, and correlations between structure and network dynamics was established by various analytical methods like light scattering (LS), 55 small angle neutron scattering (SANS), 56–59 nuclear magnetic resonance (NMR) spectroscopy, relaxometry and diffusometry 60–64 . Recently, a chemically selective analytical tool such as high‐resolution NMR has been applied to monitor the different behavior of polymer network moieties during the temperature‐induced volume‐phase transition (VPT) 63–65 . Theoretical models, like Flory‐Rehner swelling theory 66 were used to investigate microgels to obtain information about the specific polymer network parameters, or to investigate the microstructure of the particles.…”

“…[60][61][62][63][64] Recently, a chemically selective analytical tool such as high-resolution NMR has been applied to monitor the different behavior of polymer network moieties during the temperature-induced volume-phase transition (VPT). [63][64][65] Theoretical models, like Flory-Rehner swelling theory 66 were used to investigate microgels to obtain information about the specific polymer network parameters, or to investigate the microstructure of the particles. Different microgel morphologies were investigated from homopolymer microgels 58 to statistical copolymers, 60 and amphoteric microgels 67 by adapted Flory transition theory to analyze the structure, heterogeneous morphology, and network properties.…”