Fluctuation-dissipation relations for polymer systems. I. The molecular weight dependence of the viscosity |
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Authors: | M.G. Brereton A. Rusli |
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Affiliation: | Department of Physics, University of Leeds, Leeds LS2 9JT, UK |
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Abstract: | Generalised Langevin equations are used to describe the motion of interacting polymer molecules. In these equations the many-body aspects of the problem are incorporated into generalised friction functions and random forces. The so-called second fluctuation-dissipation relation gives a general relation between these two quantities and enables us to relate the spatial correlations present in the environment to a normal mode dependent friction coefficient and force constant. We then show how the various regimes of molecular weight dependence of the viscosity can be understood in a fairly general and non-specific way in terms of the spatial correlations of the random forces representing the rest of the system of polymer and solvent molecules. In particular a molecular weight dependence of M3 is shown to be a general feature of a spatially corelated environment. |
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