Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 27: Poster: (Hydrogels) and Elastomers

CPP 27.17: Poster

Wednesday, March 28, 2012, 11:00–13:00, Poster A

Local stress distributions in strained elastomers by low-field NMR — •Maria Ott¹, Martin Schiewek¹, Horst Schneider¹, Paul Sotta², and Kay Saalwächter¹ — ¹Martin-Luther-Universität Halle-Wittenberg, Faculty of Natural Science II, Betty Heimann Str 7, 06120 Halle, Germany — ²Laboratoire de physique des solides, Université Paris-Sud, Bât. 510, 91405 Orsay Cedex, France

Macroscopic strain applied to elastomeric networks induces reorientations of the constituent polymer chains. In this way, heterogeneities of the polymer matrix become apparent, reflecting a potentially non-trivial and complex distribution of local stresses, which is particulary relevant for elastomers with nanofillers. We present a general NMR approach [1] which enables to study the molecular-level effect of macroscopic strain by revealing the absolute values and the distributions of the average segmental residual dipolar couplings. These reflect the time-averaged orientation of the polymer backbone and are directly related to the local stress [2]. We demonstrate this approach using natural rubber of different cross-link densities and amounts of filler particles. We found new fractions of highly coupled (stressed) chain segments which increase with the applied strain. However, a large discrepancy of the overall increase reveals the limits of the well-established Gaussian model [3], and a new theoretical approach is discussed.

[1] K. Saalwächter, Prog. Nucl. Magn. Reson. 51, 1-35 (2007)

[2] J.-U. Sommer et al., Phys. Rev. E 78, 051803 (2008)

[3] P. Sotta, B. Deloche, Macromolecules 23, 1999-2007 (1990)