Static-gradient NMR imaging for depth-resolved molecular diffusion in amorphous regions in semicrystalline poly(tetrafluoroethylene) film

TL;DR

This study uses NMR imaging to explore how polymer chains move in different regions of a PTFE film, revealing how their movement is affected by their position near crystalline structures or surfaces.

Contribution

The paper introduces static-gradient NMR imaging to study depth-resolved diffusion in semicrystalline PTFE films, revealing interfacial dynamical heterogeneity.

Findings

Molecular mobility is constrained at the PTFE film's substrate interface due to interfacial pinning.

The air-side surface of the PTFE film shows enhanced molecular mobility.

Multiple diffusion regimes were identified in amorphous regions near crystalline lamellae.

Abstract

Understanding spatially heterogeneous molecular diffusion in semicrystalline polymers is critical for elucidating interfacial dynamics in soft materials. This study employs static-gradient nuclear magnetic resonance (NMR) imaging to capture the depth-resolved translational motion of polymer chains in a polytetrafluoroethylene (PTFE) film. By focusing on spin–spin relaxation behavior in amorphous regions near crystalline lamellae, we identify multiple diffusion regimes consistent with Bloch–Torrey analysis. The results reveal that molecular mobility at the substrate interface of PTFE film, immobilized on a glass substrate using epoxy resin, is significantly constrained, likely due to interfacial pinning, while the air-side surface shows signs of enhanced mobility. Our findings highlight the utility of static-gradient field NMR for probing nanoscale dynamical heterogeneity in semicrystalline systems.

Figures