A study of band texture formation of nematic solutions of poly(1,4‐phenyleneterephthalamide) in sulfuric acid

Abstract

Abstract The band texture formation of nematic poly(1,4‐phenyleneterephthalamide) (PPTA)/H 2 SO 4 solutions after shearing between rotating plates was studied. For a thickness of the solution layer larger than 20 μm the band texture appears immediately after the cessation of shearing, but a critical shear rate is needed which was demonstrated directly using polarizing microscopy. When the solution‐layer thickness was less than 10 μm, an induction time t b needed for the development of the band texture after the cessation of shearing was observed, which was of the order of 10 to 10 2 s. It is thus shown without any ambiguity that the band texture is formed during relaxation of shear orientation. The effects of solution concentration, solution‐layer thickness, shear rate, and shearing time on t b were studied. Once the band texture is formed from a sheared solution, it will take hours to relax completely to a randomly oriented domain texture. The factors influencing this relaxation time were also studied.