Segmental anisotropy in strained elastomers detected with a portable NMR scanner

Solid State Nucl Magn Reson. 2002 Sep-Nov;22(2-3):327-43. doi: 10.1006/snmr.2002.0067.

Abstract

Single-side NMR is particularly suitable for measurements of segmental anisotropy induced in elastomers by uniaxial forces or local strain. Proton transverse nuclear magnetic relaxation was investigated with the NMR-MOUSE by recording the Hahn-echo decay in cross-linked natural rubber bands. This provided information on the dependence of the Hahn-echo decay on the angle between the direction of the uniaxial stretching force and the axis Z defined direction perpendicular to the magnet pole faces of the NMR-scanner. The anisotropy effect on the Hahn-echo decay is correlated with the extension ratio, and it is more evident in the liquid-like regime of the decay. A weaker segmental anisotropy is detected by 1H solid- and Hahn-echo decays recorded by multi-pulse sequences. A qualitative understanding of the angular dependence is obtained by an analytical theory of the Hahn-echo decay adapted to the case of stretched elastomers and to strongly inhomogeneous magnetic fields. Using angular-dependent 1H residual second van Vleck moments and correlation times reported previously [P.T. Callaghan and E.T. Samulski, Macromolecules 30, 113 (1997)] from stretched natural rubber bands the segmental anisotropy measured in inhomogeneous magnetic fields by the Hahn-echo decay was numerically simulated. As an example of a macroscopic distribution of local segmental anisotropy, 1H Hahn-echo decays were measured by the NMR-MOUSE sensor in a stretched cross-linked natural rubber plate with a circular cut in the center.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anisotropy
  • Computer Simulation*
  • Elasticity
  • Elastomers / chemistry
  • Electromagnetic Fields*
  • Equipment Design
  • Magnetic Resonance Spectroscopy / instrumentation*
  • Magnetic Resonance Spectroscopy / methods
  • Models, Theoretical*
  • Protons
  • Rubber / chemistry*
  • Sensitivity and Specificity
  • Stress, Mechanical

Substances

  • Elastomers
  • Protons
  • Rubber