Measurement of the first normal-stress difference at high shear rates for a polyisobutylene/decalin solution “D2”

Abstract

Reasonable agreement is found between values of the first normal-stress differenceN ₁ for samples of “D2”, a polyisobutylene/decalin solution, measured in steady shear flow using three different instruments: a Weissenberg Rheogoniometer (a cone-plate rotational rheometer), a Torsional Balance (plate-plate rotational) Rheometer, and a Stressmeter (a transverse-slot slit-die rheometer). Viscosity values are also in reasonable agreement. Ranges of variables common to at least two rheometers include values of shear stressσ up to 3,700 Pa and shear rate$\dot \gamma$ up to 20,700 s⁻¹ near 25 °C. The agreement supports the approximate validity of the semi-empirical “HPBL equation” used to calculateN ₁ from Stressmeter data over a range of shear rates up to 20,700 s⁻¹ near 25 °C. Time-temperature superposition behavior exhibited by Stressmeter data at temperatures in the range 21 °C to 111 °C suggest that the range of validity of the Stressmeter method for determiningN ₁ approximately may extend up to shear rates of 290,000 s⁻¹ at 111 °C.