Rheo-Optical Studies of Liquid Crystalline Solutions of Helical Polypeptides

Abstract

Abstract The shear dependence of structures of liquid crystalline solutions of Poly-γ-benzyl-l-glutamate PBLG in m-cresol was examined in a polarizing microscope using a specially constructed shearing stage and stroboscopic illumination. Three different textures were observed depending on shear rate. The shear rates at which the texture changes occurred correlated well with the changes in sign of the first normal stress difference reported earlier.1,2 The region of negative first normal stress difference corresponded to a texture consisting of striations perpendicular to shear. The transverse striations were also observed to develop over a period of seconds or minutes after cessation of shear at rates within the first positive region of N 1, These striations could be fixed in a dried film by using a volatile helicogenic solvent (1,4-dioxane). A speculative model is proposed to account for the rheological observations in Refs.1,2 and the rheo-optical observations reported herein.