Constrained dynamics in interphases of model filled elastomers - effect of interface chemistry on crosslinking, local stress distribution and mechanics (DINaFil)
Final Report Abstract
The goal of this project was the systematic elucidation of the most important factors that govern the unique mechanical properties of particle-filled elastomers, which find applications in many everyday commodities such as tires. A Franco-German consortium jointly funded by the ANR and the DFG sought to investigate the relations between internal structure, inhomogeneous molecular dynamics, and the mechanical properties by way of preparing and studying model nanocomposites of different crosslinked polymers filled with silica particles of known and controlled particle size, surface properties and distribution. The project combined results from advanced NMR spectroscopy, scattering techniques, mechanical spectroscopy, and computer simulations, with the aim to establish quantitative structure-property relationships. At the outset, the emphasis was on as-perfect-as-possible control and systematic variation of the dispersion state of well-defined silica spheres in an elastomer matrix, with additional control of the interaction between filler and elastomer, either by chemical bonds or by adsorption. NMR investigations on an established model system based on poly(ethyl acrylate) have revealed quantitative relationships between the temperature-dependent amount of immobilized polymer at the particle surface and the size of the transition region (i.e. the “interphase”), the total internal surface and its properties (adsorptive vs. covalently binding), the dispersion state, and the linear and non-linear mechanical properties (e.g. strain softening). Notably, only model systems with dense chemical surface grafts exhibited an additional pronounced inhomogeneity of the surrounding rubber matrix, accompanied by rather high amounts of immobilized polymer. Studies on various other silica-filled diene elastomers such as natural rubber (NR) or styrene-butadiene-rubber (SBR) demonstrated this to be a peculiarity of the model system, as in the latter systems it was found that filler addition does not lead to significant changes in the crosslinking state of the matrix or to large quantities of immoblized components. Rather low but systematically varying amounts of immobilized interphase material could reliably be identified in the SBR/silica system, where a universal relation to the surplus elasticity modulus of the filler network measured at variable temperature and agitation frequency could be established. In-depth investigations of the dynamic interphase in the model systems revealed the quantitative applicability of a glass transition temperature gradient model, by way of which NMR observables could be used for a parameter-free prediction of the thermal (calorimetric) response of the same system. More advanced so-called spin-diffusion NMR experiments served to estimate the size of the dynamic interphase, and revealed that the laterally averaged 1D gradient model is only an approximation in a sense that the systems are characterized by dynamic heterogeneities on the nm scale. Finally, NMR studies of stretched filled und unfilled rubbers enabled the quantitative assessment of chain stretching on a microscopic level. In this way, in the former case we were able to experimentally confirm theoretical predictions of the so-called matrix overstrain in filled rubbers, related to the fact that the filler particles are not deformable. In the latter case, our wealth of new NMR observables was used to assess the validity of different theoretical approaches to entangled rubber elasticity, thus contributing to solving long-standing open questions.
Publications
- Angew. Chem. Int. Ed. 50, A63-A70 (2011) [Review; special DFG issue]
F. Lequeux, D. Long, P. Sotta, K.Saalwächter
(See online at https://doi.org/10.1002/anie.201105813) - Low-Field NMR Investigations of Nanocomposites: Polymer Dynamics and Network Effects. Macromolecules 44, 913 (2011)
A. Papon, K. Saalwächter, K. Schäler, L. Guy, F. Lequeux, H. Montes
- Glass-Transition Temperature Gradient in Nanocomposites: Evidence from Nuclear Magnetic Resonance and Differential Scanning Calorimetry. Phys. Rev. Lett. 108, 065702 (2012)
A. Papon, H. Montes, M. Hanafi, F. Lequeux, L. Guy, K. Saalwächter
(See online at https://doi.org/10.1103/PhysRevLett.108.065702) - Mechanical properties and cross-link density of styrenebutadiene model composites containing fillers with bimodal particle size distribution. Macromolecules 45, 6504 (2012)
A. Mujtaba, M. Keller, S. Ilisch, H.-J. Radusch, T. Thurn-Albrecht, K. Saalwächter, M. Beiner
(See online at https://doi.org/10.1021/ma300925p) - Proton NMR spin diffusion studies of PS-PB block copolymers at low-field: two- vs. three-phase model and recalibration of spin-diffusion coeffcients. Polym. J. 44, 748 (2012)
H. W. Meyer, H. Schneider, K. Saalwächter
(See online at https://doi.org/10.1038/pj.2012.88) - Kautsch. Gummi Kunstst. (KGK) 66, 52 (2013) (Review)
A. Papon, T. Chaussée, L. Guy, K. Saalwächter, J. Oberdisse, S. Merabia, D. Long, P. Sotta, H. H. Frielinghaus, A. Radulescu, B. Demé, L. Noirez, H. Montes, F. Lequeux
- Local Chain Deformation and Overstrain in Reinforced Elastomers: An NMR Study. Macromolecules 46, 5549 (2013)
R. Pérez-Aparicio, M. Schiewek, J. López Valentín, H. Schneider, D. R. Long, M. Saphiannikova, P. Sotta, K. Saalwächter, M. Ott
(See online at https://doi.org/10.1021/ma400921k) - Sulfur-Cured Natural Rubber Elastomer Networks: Correlating Cross-Link Density, Chain Orientation, and Mechanical Response by Combined Techniques. Macromolecules 46, 889 (2013)
A. Vieyeres, R. Pérez-Aparicio, P.-A. Albouy, O. Sanseau, K. Saalwächter, D. R. Long, P. Sotta
(See online at https://doi.org/10.1021/ma302563z) - Detection of Surface-Immobilized Components and Their Role in Viscoelastic Reinforcement of Rubber−Silica Nanocomposites. ACS Macro Lett. 3, 481 (2014)
A. Mujtaba, M. Keller, S. Illisch, H.-J. Radusch, M. Beiner, T. Thurn-Albrecht, K. Saalwächter
(See online at https://doi.org/10.1021/mz500192r) - Microscopic Study of Chain Deformation and Orientation in Uniaxially Strained Polymer Networks: NMR Results versus Different Network Models. Macromolecules 47, 7597 (2014)
M. Ott, R. Pérez-Aparicio, H. Schneider, P. Sotta, K. Saalwächter
(See online at https://doi.org/10.1021/ma5012655) - NMR study of interphase structure in layered polymer morphologies with mobility contrast: disorder and confinement effects vs. dynamic heterogeneities. Colloid Polym. Sci. 292, 1825 (2014)
M. Roos, K. Schäler, A. Seidlitz, T. Thurn-Albrecht, K. Saalwächter
(See online at https://doi.org/10.1007/s00396-014-3218-8)
