Microscopic Study of Chain Deformation and Orientation in Uniaxially Strained Polymer Networks: NMR Results versus Different Network Models

Abstract

The complex pathway of transmitted stress and strain within elastic networks affects the conformations of single network chains in a complex and inhomogeneous manner. For a novel experimental assessment, we investigated moderately to highly cross-linked vulcanized natural rubber networks with proton multiple-quantum NMR and studied the correlation between macroscopic uniaxial elongation and local effects of strain and/or confinement on the level of elastically active subchains. Our method and the data treatment allow for a separate analysis of chain deformation and orientation, which in turn allows for critical comparisons of our experimental results with predictions from various network models. Specifically, comparisons with the affine fixed-junction model, the phantom model, and different tube models allowed us to draw conclusions on the presence of possibly tube-related local confinement effects. As none of the models alone was able to provide a comprehensive, quantitative description of all experimental data, we performed numerical calculations inspired by earlier simulation results, which match the data and support the presence of two distinct populations of network chains that are either more or less stretched as well as oriented.