Rheo-Optical Studies of Liquid Crystalline Solutions of Helical Polypeptides

Abstract

The shear dependence of structures of liquid crystalline solutions of Poly-y-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.'~* 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 , . These striations could be fixed in a dried film by using a volatile helicogenic solvent (1,4-droxane).A speculative model is proposed to account for the rheologicdl observations in Refs.'.' and the rheo-optical observations reported herein.

Polypeptides and 100 Years of Chemistry of α‐Amino Acid N‐Carboxyanhydrides

“…The macroscopic consequences of the molecular mobility were studied by means of rheological measurements. [240][241][242] These measurements included both poly(g-Bzl-l-Glu) and poly(N e -Z-l-Lys) but were restricted to solutions in metacresol. Temperatures, concentration, and molecular weights of the polypeptides were varied.…”

Polypeptide und 100 Jahre Chemie der α‐Aminosäure‐N‐carboxyanhydride

“…Die makroskopischen Auswirkungen der molekularen Beweglichkeit wurden mit rheologischen Messungen verfolgt. [240][241][242] Diese Messungen wurden sowohl an Poly(gBzl-l-Glu) als auch an Poly(N e -Z-l-Lys) durchgeführt, beschränkten sich aber auf Lösungen in meta-Kresol. Dabei wurden Temperatur, Konzentration und Molmassen der Polypeptide variiert.…”

An electron diffraction analysis of banded structures in thermotropic polymers

“…This same banded structure has recently been observed in a range of thermotropic polymers oriented by shear [2], as well as other lyotropic systems [3,4]. Observation of sheared thermotropic polymers using polarised light microscopy and transmission electron microscopy [5,6] has shown that the banded structure arises from a serpentine trajectory of the molecules about the shear axis.…”

“…Figure 9 compares the profiles of the equatorial reflections (SAED) for specimens prepared at T~ --300, 240 and 200 ~ The angular spread is much reduced at the lower temperatures (the T~ = 200 and 240 ~ curves essentially superimpose) indicating that the swing in orientation about the shear direction is decreased. If the banded structure arises as a relaxation phenomenon, as has been suggested [3,6], the slower rate of "disorientation" at the lower temperature might be expected, but a more detailed explanation for the observation must await a clearer understanding of the mechanism of formation of the structure itself. .…”