M. Ott, R. Pérez-Aparicio, H. Schneider, P. Sotta, K. Saalwächter.
Microscopic Study of Chain Deformation and Orientation in Uniaxially Strained Polymer Networks: NMR Results versus Different
Macromolecules 47, 7597-7611 (2014).
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.