Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
We propose a new model for the Lamb-Matheson-Philippoff (LMP) increment in the dynamical viscosity of polystyrene solutions. The crucial difference between the new model and the currently accepted models is that our model predicts that at least a large part of the LMP increment relaxes at a particular frequency, whereas the conventional models predict a nonrelaxing increment. In order to derive our model, we reformulate the internal viscosity (IV) concept, for a fluid undergoing shear, in such a way that the shear filed appears explicitly in the IV resistance. Since the derivation of this IV model is nonrigorous and produces a result which may be surprising, we rederive the dynamical viscosity using a correlation function technique, into which the flow field does not enter explicitly. We show that our model predicts the principal experimental results on the LMP increment as well as the conventional models do, but that our model gives a result which is more in line with current thinking (i.e., that the increment might be expected to undergo relaxation). We also show that our model accurately predicts an “anomalous” result obtained recently on the viscoelastic absorption spectrum of poly(propylene glycol) melts, the description of which is quite outside the scope of the Rouse-Zimm model or the currently accepted IV model.
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