Mapping structures and dynamics with frequency-correlated diffusion exchange.

Area of Science:

• Soft Matter Physics
• Polymer Science
• Analytical Chemistry

Background:

• Understanding molecular motion in complex environments is crucial for materials science and chemical engineering.
• Heterogeneous systems often obscure diffusion pathways, limiting insights into material behavior.

Purpose of the Study:

• To develop a novel multidimensional nuclear magnetic resonance (NMR) method for characterizing molecular motion across dynamic regimes.
• To reveal diffusion pathways obscured in heterogeneous soft matter systems.
• To link molecular motion to material topology and chemical state for advanced property extraction.

Main Methods:

• Extension of the modulated gradient spin-echo technique with frequency-frequency correlations.
• Implementation on a unilateral NMR magnet to access kilohertz dynamics without gradient pulsing constraints.
• Application to polymer swelling and acid-catalyzed deconstruction processes.

Main Results:

• The method successfully captures molecular population exchange between different dynamic regimes.
• Diffusion pathways in heterogeneous polymer systems were revealed.
• Physical metrics like fractal surface dimensionality and reaction wavefront velocity were extracted, which are inaccessible with standard methods.

Conclusions:

• The developed multidimensional NMR technique enhances the study of soft matter dynamics.
• This approach has significant implications for polymer recycling and the design of sustainable materials.
• The method provides unprecedented insights into the evolution of structural heterogeneity over time.