Describe NMR relaxation by anomalous rotational or translational diffusion

TL;DR

This paper introduces a fractional diffusion approach to model NMR relaxation, effectively fitting experimental data and revealing new temperature dependence behaviors in polymer segmental dynamics.

Contribution

It develops a novel fractional diffusion framework for NMR relaxation analysis, providing more accurate and convenient fitting methods compared to traditional models.

Findings

Excellent fit to experimental NMR relaxation data.

Temperature dependence may follow a different VTF behavior.

New formalism enhances analysis of macromolecular NMR experiments.

Abstract

This paper employs the general time-space fractional diffusion equation to derive correlation time function for analyzing nuclear magnetic resonance (NMR) relaxation. Both the anomalous rotational and translational diffusion are treated. NMR relaxation time affected by various Hamilton interactions such as dipolar or quadrupolar couplings can be calculated from the Mittag-Leffler type time correlation and their corresponded spectral density functions obtained. Additionally, to verify the results, the theoretical expressions are applied to fit reported experimental data of NMR quadrupolar coupling relaxation of head-to-head poly(propylene) (hhPP) in a polymer blend. The fitting is excellent and more convenient than the fitting utilizing the traditional modified Kohlrausch-Williams-Watts (KWW) formalism. Further, it is found that the temperature dependence behavior of the segmental dynamics in anomalous diffusion may obey a different Vogel-Tamman-Fulcher (VTF) expression. The paper proposes new, general formalisms for analyzing various NMR relaxation experiments in macromolecular systems.