11 - Rheological Properties of Poly-p-Phenyleneterephthalamide/H2SO4 Solutions

Abstract

The rheological properties of solutions of poly-p-phenyleneterephthalamide in sulfuric acid (PPT/H2SO4) have been studied in both the lyotropic and isotropic states to determine whether certain behavior can be attributed to liquid crystalline order. The rheological experiments include frequency sweeps, steady shear, creep, and start up of steady shear flow. Several of the phenomena commonly reported to describe liquid crystalline polymers (e.g., three region flow curve, negative steady state first normal stress difference, and oscillatory behavior upon inception of steady shear) are not observed in either solution. The solution in its anisotropic state exhibits a two region flow curve (at rates ranging from 10-4 to 102 sec-1), a positive steady state first normal stress difference which increases with shear rate, a transient first normal stress difference which increases monotonically to a steady state value, and a transient shear stress which displays a single overshoot before reaching a steady state value. The small amplitude dynamic oscillatory material functions agree well with the corresponding functions measured in steady shear flow (e.g., η ≈η and N12G′).