Deuterium Nuclear Magnetic Resonance of Phenol-d5 in Nylon 6 under Active Uniaxial Deformation

Abstract

A stretching device suitable for fitting within a deuterium nuclear magnetic resonance (NMR) probe was constructed to investigate the large strain uniaxial tensile deformation behavior of nylon 6 plasticized by 40 wt % of phenol-d5. The phenol-d5 molecules probe the environment of the amorphous regions in nylon 6; the phenol-d5 molecules do not exist in a “free” state, and they remain associated with the amide groups by hydrogen bonding during deformation. Deuterium NMR spectra show that the quadrupolar splitting varies linearly with strain throughout the experiment, indicating that the orientation of the phenol-d5 molecules in the amorphous phase is simply a function of strain and not of stress. The line width increases with strain at low-to-moderate strains but attains a constant value at large strains (in the strain-hardening regime). From low-to-moderate strains, the line width behavior arises from a decrease in the translational motion of the phenol-d5 molecules between amide groups in the amorphous chains during elastic deformation and during the transformation of the lamellar structure of nylon 6 to a fibrillar one. At large strains, the existence and deformation of the fibrillar structure cause the phenol-d5 molecules to be confined to their respective amide groups on the time scale of the NMR measurement (∼0.1 ms), resulting in a constant line width.