Structure-mechanical property correlations of model siloxane elastomers with controlled network topology |
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Authors: | Kenji Urayama [Author Vitae] Takanobu Kawamura [Author Vitae] [Author Vitae] |
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Affiliation: | a Department of Materials Chemistry, Kyoto University, Kyoto 615-8510, Japan b Department of Chemical Engineering, Kanazawa University, Ishikawa 920-1192, Japan c Department of Chemistry, Mahidol University, Phuthamonthon, Nakorn Pathom 73170, Thailand |
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Abstract: | We review our recent studies towards the molecular understanding of mechanical properties-structure relationships of elastomers using model polydimethylsiloxane (PDMS) networks with controlled topology. The model elastomers with controlled lengths of the network strands and known amounts of cross-links and dangling chains are obtained by end-linking the functionally terminated precursor PDMS with known molecular weights using multi-functional cross-linkers. Several modern entanglement theories of rubber elasticity are assessed in an unambiguous manner on the basis of the nonlinear stress-strain behavior of the model elastomers under general biaxial strains. The roles of cross-links and entanglements in the large-scale structure of the swollen state are revealed from small angle X-ray scattering spectra. A remarkably stretchable elastomer with the ultimate strain over 3000% is obtained by optimizing the network topology for high extensibility, i.e., by reducing the amounts of trapped entanglements and the end-to-end distance of the network strands. The model elastomers with unattached chains exhibit a pronounced viscoelastic relaxation originating from the relaxation by reptative motion of the guest chains. The relaxation spectra provide a definite basis to discuss the dynamics of guest linear chains trapped in fixed polymer networks. The temperature- and frequency-insensitive damping elastomers are made by introducing intentionally many dangling chains into the networks. |
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Keywords: | Elastomers Polydimethylsiloxane Rubber elasticity Viscoelasticity |
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