Sinusoidal Supermolecular Structure of Band Textures in a Presheared Hydroxypropyl Cellulose Film

Abstract

ABSTRACT:A morphological study of hydroxypropyl cellulose (HPC) has been performed on solid films prepared by casting from a presheared liquid crystalline aqueous solution. Band textures were observed in a polarizing optical microscope. The sinusoidal supermolecular structure associated to the band texture was verified plausibly by comparison between the changes of experimental micrographs and theoretical birefringence patterns with the rotation of specimen. Some viewpoints in literature were commented. The pleated morphology was also confirmed in a scanning electron microscope.KEY WORDS Liquid Crystalline Polymer/ Band Texture/ Supermolecular Structure / Hydroxypropyl Cellulose / Polarized Optical Microscopy / Liquid crystalline polymer (LCP) exhibits distinct physical properties not to be expected in flexible polymers as well as in low molecular liquid crystals. One of interesting and puzzling phenomena is the band texture, which is common to all main chain LCP. The alternating dark and bright bands perpendicular to the preshearing direction was first observed in a polarizing microscope by Elliottt and Ambrose 1 from a solution cast film of poly(y-benyl-L-glutamate) (PBLG), which was long before LCP became of wide interest since the appearance of Kevlar, a famous highmodulus fiber. The band texture was then observed in the very Kevlar 2 and many other many chain LCPs. 3 -32 The bands are formed usually during shear relaxation, although occasionally, they can also be found during shear, 29 or during elongation relaxation, 27 or even without any noticeable macroscopic orientation. 26 A peculiar side chain LCP with mesogenic units attached directly in a sideon mode can also exhibit band texture in the sheared specimen. 33 Besides of interest in the light of the fundamental research, the 1132 band texture affects the mechanical properties of LCP materials very much 28 and, therefore, has attracted much attention of scientists and engineers.

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

“…In the latter case, the birefringent bands can result from the wavy bending growth or twisting growth of crystals. The wavy bands have been reported in sheared liquid crystals [4,5], which do not form spherulites under the condition. In this mini-review, we focus on the birefringent banded spherulites, which consist of synchronously twisted lamellar crystals.…”

Solitons and defects in nematic liquid crystals under a simple shear flow and in a static external magnetic field

“…The operator L is defined as L= K For the case of critical nucleus, the eigenvalue equation is written as (25) where ξ C is defined in Eq. (18).…”

“…[22,23] On the other hand, after the cessation of shear flow the patterns are basically the band structure. [18,24,25] It is generally believed that nematics of the tumbling type should be the candidate for the production of defects [26] due to their propensity for various flow instabilities. However, the situation is not so simple as expected.…”