NMR surface relaxivity in a time-dependent porous system

TL;DR

This paper investigates the unusual decay and recovery of NMR relaxation times in water within a hydrating porous material, revealing the importance of time-dependent surface relaxivity for accurate interpretation.

Contribution

It introduces the concept of temporally evolving surface relaxivity to explain complex NMR relaxation behavior in dynamic porous systems.

Findings

Observed decay-recovery in NMR relaxation times during hydration.

Transition between surface-limited and diffusion-limited regimes.

Highlights limitations of classical NMR analysis in evolving systems.

Abstract

We demonstrate an unexpected decay-recovery behaviour in the time-dependent $^{1}\mathrm{H}$ NMR relaxation times of water confined within a hydrating porous material. Our observations are rationalised by considering the combined effects of decreasing material pore size and evolving interfacial chemistry, which facilitate a transition between surface-limited and diffusion-limited relaxation regimes. Such behaviour necessitates the realisation of temporally evolving surface relaxivity, highlighting potential caveats in the classical interpretation of NMR relaxation data obtained from complex porous systems.