Abstract
The steady-flow and dynamic properties of polyethylene melts measured with a rotating cylinder type rheometer have been compared with the current theories and existing data on the relation between the steady-flow and dynamic viscosities. Contrary to the prediction of DeWitt, the dynamic viscosity η' vs. angular frequency (ω) curve decreases earlier than does the apparent viscosity ηa vs. rate of shear (D) curve, and these curves cannot be superposed by simple shifting along the abscissa. Pao's theory is not necessarily be applicable to our experimental results: the dynamic fluidity J"ω (J" is the loss compliance) vs. ω curve is not always the same as the apparent fluidity 1/ηa vs. D curve. The empirical law originated by Cox and Merz fits very well to our results, and the ηa vs. D curve coincides very well with the |η*| vs. ω curve, where |η*| is the absolute value of complex viscosity. Nevertheless, the consistency ηc or the differential viscosity ηd is not the same as η', contrary to Strella's theory. Our finding might closely be connected with the essential difference in linearity between the steady-flow and the dynamic behavior.
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