| Abstract: | The viscosity of solutions of poly(decyl methacrylate)s, PDMA, in 1-pentanol (thermodynamically poor solvent) and in toluence or isooctane (good solvents) was measured up to shear rates of 3 · 104s?1 by means of rotational viscosimeters. The observed pronounced shear thinning is for all solutions well described by the theory of Graessley, with the extension, introduced by Ito. Two parameters, resulting from the evaluation of the flow curves on the basis of the above theory, are discussed: τ0, a characteristic relaxation time of the polymer chain, is found to be in the range of ms. ηfric, a frictional parameter, independent of shear rate, amounts upto 50% of the zero-shear viscosity for the measured solutions. Both, τ0 and ηfric, increase with decreasing solvent quality, increasing molecular weight, and increasing concentration, in accord with theory. A comparatively sharp downward bend, separating two power-law regimes, shows up with moderately concentrated solutions, as the shear rate exceeds about 103 to 104 s?1. This transition is tentatively interpreted as an orientation of the long side chains of PDMA. |
