ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The shear dependence of viscosity of alfin polyisoprene in dilute benzene solutions at 25°C. was studied over a wide range of molecular weights. The polyisoprene was prepared initially to amolecular weight of about 4,500,000, and a number of portions of the polymer were allowed to degrade to various intermediate molecular weights down to about 200,000 followed by stabilization at these particular molecular weight levels. This procedure provided a wide range of molecular weights without recourse to the usual fractionation. Inherent viscosities were measured in an Ostwald-Fenske viscometer at rates of sher from about 1000 to 10,000 sec.-1 and at concentrations from about 0.05 down to 0.01 g./dl. Some data were also obtained in a series of similar viscometers of different radii. It was found that both the inherent and the intrinsic viscosities of the Alfin polyisoprene depend strongly on the rate of shear, the effect increasing with increasing molecular weight. Moreover, the shear dependence of the inherent viscosity is best expressed by an equation involving both a linear and a quadratic function of the gradient. The experimental data were examined from the standpoint of Katchalsky's proposed method for obtaining simply and rapidly the zero shear viscosity from measurements in an Ostwald-type viscometer. According to this method, a plot of ts/t vs. P2R2, where ts and t are the flow times of the (Newtonian) solvent and (non-Newtonian) solution, P the applied pressure, and R the radius of the capillary, should be linear, and the intercept of this line at P2 = 0 or R2 = 0 gives the reciprocal of the relative viscosity at zero shear. The agreement between the zero shear viscosities obtained by the Katchalsky method and from the conventional viscosity-shear curves was only fair. Above a molecular weight of about 280,000 the Katchalsky values are consistently smaller than the corresponding values obtained from the viscosity-shear curves, and furthermore this discrepancy increases with molecular weight. Because of this discrepancy, an attempt was made to modify the Katchalsky equation, so as to bring the respective zero shear viscosities in to better agreement. It was found that an anlogous equation, calling for a linear plot of ts/t vs. PR, provided a rather accurate measure of the zero shear viscosity.
Additional Material:
16 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1955.120188703
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