title: Segmental anisotropy in strained elastomers detected with a portable NMR scanner.
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.
authors.affiliation: Institut für Technische Chemie und Makromolekulare Chemie, Rheinisch-Westfalische, Technische Hochschule, Worringerweg 1, D-52056 Aachen, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Hailu
authors.forename: R
authors.initials: R
authors.lastname: Fechete
authors.forename: D E
authors.initials: DE
authors.lastname: Demco
authors.forename: B
authors.initials: B
authors.lastname: Blümich
mesh_terms: D016880:Anisotropy; D003198:Computer Simulation; D004548:Elasticity; D020724:Elastomers / Q000737:chemistry; D004574:Electromagnetic Fields; D004867:Equipment Design; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D008962:Models, Theoretical; D011522:Protons; D012408:Rubber / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical
chemical_list: D020724:Elastomers; D011522:Protons; D012408:Rubber