Determination of normal stress differences in steady shear flow

Summary Using the cone- and-plate apparatus ofAdams andLodge, values of pressure gradient,r-d¯p/dr in a range 300 to 3000 dyn/cm², have been measured to an accuracy of 1% at shear rates near 10 sec^–1 in liquids of viscosity less than 200 poise. Using the constancy of pressure gradient at a given shear rate as an indicator of liquid stability, it was found that a polyisobutene liquid containing 2% of Oppanol B 200 in Oppanol B I, when stored at rest at 25 °C, was stable during a certain 7-day period after dissolution and unstable during the subsequent 30 days.