Modeling 1H NMR transverse magnetization decay in polysiloxane-silica composites

Abstract

Abstract Nuclear magnetic resonance (NMR) spectroscopy has been used effectively in the analysis of elastomeric, soft materials and has been proven to be both sensitive to micro- and macroscopic changes associated with “aging” mechanisms. Traditional analyses, however, rely on empirical formulae containing a large number of (often arbitrary) independent variables. The resulting ambiguity can be circumvented largely by developing models of NMR observables that are based on basic polymer physics. We compare two such models, one previously published and one derived herein, along with two empirical expressions that describe the proton transverse magnetization decay associated with complex polymer networks. One particular extracted parameter, the proton–proton residual dipolar coupling (RDC), can be directly related to network topology, and a comparison of the extracted RDCs reveals high consistency among the models. An expression derived from the properties of a static Gaussian chain can minimize the number of parameters necessarily to describe the solid-like, networked proton population to a single independent parameter, the average RDC, D avg . The distribution of RDCs derived via this methodology is qualitatively similar to those derived from previously published multiple quantum techniques, although quantitative differences between the derived RDCs persist, suggesting that further analysis is necessary.