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Poly(1,4-butadiene) networks obtained by a 4-functional random cross-linking reaction over a broad range of polymer concentration were studied by small angle neutron scattering(SANS), 2H NMR and Monte Carlo(MC) simulation in the isotropic and uniaxially deformed state. The defect structure of the networks has been characterized by MC simulation of the cross-linking reaction. The anisotropy of the radius of gyration in deformed networks determined from SANS has been analyzed by the theory of Ullman. It was found that the number of active cross-links per chain is in agreement with MC and that the chain deformation follows phantom behaviour. The local orientation as measured by 2H NMR is related to the global anisotropy of the network by a MC calculation of oriented chains. The 2H NMR line shape of the deformed network is analyzed in terms of two relaxation processes arising from interior parts of the chains and from segments at chain ends. The mobility of both decrease with strain. It was found that the orientation connected to the first process shows the classical strain dependence of rubber elasticity, whereas the second exhibits a weaker dependence on strain. 相似文献
844.
Michael Wübbenhorst Ernout M. Van Koten John C. Jansen Wim Mijs Jan van Turnhout 《Macromolecular rapid communications》1997,18(2):139-147
The molecular dynamics of amorphous and liquid-crystalline (LC) side-chain polycarbonates was studied by dielectric spectroscopy at frequencies from 10−2 to 106 Hz and at temperatures from −160 to 180°C. ‘Model’ compounds containing no mesogenic side-groups showed two relaxations, which originate from the carbonate group (α, βm-relaxation). By contrast, in LC-polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature Tg up to three relaxation modes were distinguished (α-, λ1-, λ2-process); below Tg four secondary relaxations (γ-, βm-, βs-, βsc-relaxation) were observed. The γ-relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from βm-, two additional β-processes were identified as relaxations associated with the mesogenic unit in the glassy (βs) or in the crystalline state (βsc). 相似文献
845.
Peter A. Cuypers George M. Willems H. Coenraad Hemker Wim Th. Hermens 《Macromolecular Symposia》1988,17(1):155-159
A model for protein adsorption kinetics is presented. This model includes diffusion limited adsorption, adsorption and desorption rate constants which are dependent on the surface concentration and an interaction term for the mutual influence of the adsorbed protein molecules. It is shown that, in first approximation, the values of the adsorption and desorption rate constants are exponential functions of the surface concentration. Assuming an adequate interaction term it is possible to show with this model for the adsorption kinetics of a mixture of proteins that the ratio of the adsorbed proteins is strongly dependent on the overall surface concentration even if the ratio of the bulk concentrations of these proteins is kept constant. Differences in interaction terms for the different proteins offer a possible explanation for the peculiar behaviour of plasma protein adsorption on a surface at different dilutions of the plasma, the so called “Vroman effect”. 相似文献
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