FLOW BIREFRINGENCE OF POLYMER-SOLUTIONS IN TIME-DEPENDENT FIELD - RELATION BETWEEN NORMAL AND SHEAR STRESSES ON APPLICATION OF STEP-SHEAR STRAIN

The time-dependent flow birefringence was measured on application of a step—shear strain for an 8% polystyrene solution in chlorinated biphenyl. Measurements were performed with an apparatus of coaxial cylinder type at various shear strains y ranging from 0.913 to 7.56. The amount of birefringence was in agreement with that evaluated from the shear stress with the use of the stress-optical law. The extinction angle x was independent of time and satisfied a relation 2 cot 2x = T-This result combined with the stress-optical law indicates that the Lodge-Meissner relation holds valid for the polystyrene solution, i.e., the first normal stress difference is equal to the shear stress multiplied by the shear strain in the stress relaxation process following an application of step—shear strain. © 1979, The Society of Rheology. All rights reserved.