1 / 20

Local chain deformation and stress distribution in strained elastomers

Local chain deformation and stress distribution in strained elastomers. Maria Ott, Horst Schneider, Kay Saalwächter Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Halle (Saale), Germany Roberto Pérez-Aparicio, Paul Sotta CNRS-Rhodia joint lab, Lyon, France.

shalom
Download Presentation

Local chain deformation and stress distribution in strained elastomers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Local chain deformation and stress distribution in strained elastomers Maria Ott, Horst Schneider, Kay Saalwächter Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Halle (Saale), Germany Roberto Pérez-Aparicio, Paul Sotta CNRS-Rhodia joint lab, Lyon, France

  2. Uniaxial stretching of polymer networks macroscopic z x R R ? microscopic

  3. Uniaxial stretching of polymer networks macroscopic z x R R a microscopic

  4. Segmental order parameter Segmental (backbone) order parameter Sb = second moment of orientation distribution function, time-averaged f r R R0: separation of closest constraints (x-links or entanglements) f Sommer, J.-U. et al., Phys. Rev. E, 2008, 78, 051803  The segmental oder parameter directly reports on local stretching and stress

  5. Segmental order parameter Anisotropic dipole-dipole interaction Segmental (backbone) order parameter Sb = second moment of orientation distribution function,time-averaged f H H B0 Multiple-quantum NMR experiment r R t = ms (… s) f B0 Sommer, J.-U. et al., Phys. Rev. E, 2008, 78, 051803 Saalwächter, K., Prog. Nucl. Mag. Res. Sp., 2007, 51, 1-35  The NMR residual dipolar interaction measures the local stress

  6. MQ NMR spectroscopy f R a f • MICROSCOPIC DEFORMATION: • Time-domain multiple-quantum NMR experiment, raw data: • Determination and removal of the DEFECT contribution(isotropic, Dres = 0) • Localstress distributions of the NETWORKafter processing

  7. MQ NMR spectroscopy di f da R a f • MACROSCOPIC DEFORMATION: remove orientation effect! B0  l Mean stretching: • MICROSCOPIC DEFORMATION: • Time-domain multiple-quantum NMR experiment, raw data: • Determination and removal of the DEFECT contribution(isotropic, Dres = 0) • Localstress distributions of the NETWORKafter processing

  8. MQ NMR spectroscopy f R a f Bruker minispec mq20 0.5 T (20 MHz) ~ € 75.000.-

  9. Natural Rubber Local stress distribution in the unstretched network: probability Vulcanized NR (Mc=1200kg/mol)  Low defect content (~5 vol%)  Very homogeneous network

  10. Uniaxially strained natural rubber Local stress distributions in strained networks: l=1.0 l=4.2 probability orientation effect removed!  Increased heterogeneity: appearance of highly strained polymer chains

  11. Uniaxially strained natural rubber Local stress distributions: Average local stress: l=1.0 l=4.2 probability • Mc • 1102 kg/mol • 1200 kg/mol • 2100 kg/mol Me ~3900 kg/mol  Increased heterogeneity: appearance of highly strained polymer chains  Increased average dipolar interaction (local stress)

  12. Uniaxial deformation of filled networks macroscopic z x microscopic ?

  13. Silica-filled natural rubber Effect of filler particles (silica,  =18 vol%): Local strain enhancement: filled unfilled  Local overstrain effects – NMR is the only method to detect this in real-life sampes!

  14. Silica-filled natural rubber Effect of filler particles (silica,  =18 vol%): Local strain enhancement: filled unfilled Model of a polydisperse system of hard spheres: R. Christensen, Mechanics of Composite Materials Wiley, New York,1979.  Local overstrain effects are in agreement with simple hydrodynamic prediction

  15. Silica-filled natural rubber Effect of filler particles (silica,  =18 vol%): Distribution widths: filled unfilled  Higher level of local stress inhomogeneity in filled rubber

  16. Network models fixed junction affine deformation Natural rubber Mc=1200 g/mol Mc=2100 g/mol 1  Experiments reveal a strongly sub-affine behaviour !

  17. Network models fixed junction [1] [2] Mc=1200 g/mol [3] Mc=2100 g/mol 1 [4] [1] Beltzung, M, et al., Macromolecules, 1984, 17, 663-669 [2] Ronca, G. , Allegra, G., J. Chem. Phys., 1975, 63, 4990-4997 [3] Pearson, D. S., Macromolecules, 1977, 10, 696-701 [4] Heinrich, G. & Straube, E., Acta Polym., 1984, 35, 115-119

  18. Comparison with literature Small-angle eutron scattering data (end-linked PDMS): R║/R0 R a R║ R┴ Beltzung, M. et al.; Macromolecules, 1984, 17, 663-669 • - Similar results for small netwok chain molecular weights • - Experimental difficulties: end-linked networks  high defect content • Experimental difficulties: • long deuterated chains  several crosslinkes per chain • end-linked network chains  high defect content • non-trivial scattering background

  19. Conclusions Local stress distributions of strained elastomeric networks: - Measured directly by low-field MQ NMR, after removal of low (!) defect contributions - Substantial stress inhomogeneity upon stretching • Local overstrain effects in filled elastomers: • - Average follows simple hydrodynamic predition • - More pronounced stress inhomogeneity • Deviations from the fixed-junction Gaussian chain model on the molecular level • - Junction fluctuations need to be allowed • Local constraints play a role at low stretching degrees • - Force equilibration may explain narrow distributions

  20. THANK YOU FOR YOUR ATTENTION ! DINaFil: Dynamics in the Interphase of Nanoscopic Fillers Maria Ott Horst Schneider Martin Schiewek Paul Sotta Roberto Pérez-Aparicio Juan López Valentín

More Related