Deuterium nuclear magnetic resonance of deuterium oxide in nylon 6 under active uniaxial deformation

The large strain uniaxial tensile deformation behavior of nylon 6 plasticiz ed by deuterium oxide is investigated by an in situ stretching device built in a deuterium nuclear magnetic resonance (NMR) probe. The D2O molecules p robe the environment of the amorphous regions in nylon 6; they do not exist in a "free" state and 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, indicatin g that the orientation of the D2O molecules in the amorphous regions is sim ply a function of strain and not of stress. The line width increases rapidl y with strain at low to moderate strains but more slowly at large strains ( in the strain-hardening regime). From low to moderate strains, larger chang es in line width arise from a decrease in the translational motion of the D 2O molecules between amide groups in the amorphous chains during elastic de formation and during the transformation of the lamellar structure of nylon 6 to a fibrillar one. At large strains, the existence and deformation of th e fibrillar structure cause a slower decrease in the translational motion o f the plasticizer. (C) 2000 Elsevier Science Ltd. All rights reserved.