Sodium NMR relaxation: A versatile non-invasive tool for the monitoring of phase transitions and the estimation of effective pore sizes of supramolecular hydrogels

Abstract

Nuclear magnetic resonance (NMR) relaxometry of liquids is a widely used tool to characterize porous media. In particular,23Na NMR is an especially suitable method when applied to gels and biological tissues. In this work we investigated the thermoreversible melting and gelation processes of supramolecular hydrogels formed by succinamic acid-based amphiphiles (SAn) in a saturated aqueous NaHCO3 solution (sat. aq. NaHCO3 sol.). We could show that it is not only possible to determine the melting points and to monitor the gelation process with23Na relaxometry, but also to estimate the effective pore size based on the expanded Brownstein-Tarr model. Our findings are in good agreement with data from differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) experiments.