Scattering Studies on Fingerprint Texture of Cyanoethyl Chitosan

Abstract

KEY WORDSSmall-Angle Light Scattering / Chitosan / Cyanoethyl Chitosan / Lyotropic Liquid Crystal / Fingerprint Texture / Pitch / Cholesteric Phase / Small-angle light scattering (SALS) was first introduced to polymeric research by Stein 1 in 1960. Since then, it has been widely used to investigate the submicrostructures of polymers, especially spherulites. However relatively few works have concentrated on liquid crystals using SALS. In this paper, a new method to measure the pitch of fingerprint texture of liquid crystalline phase was reported. EXPERIMENTAL MaterialO-Cyanoethyl chitosan was synthesized at this lab by mixing 0.5 g chitosan (degree of deacetylation, 78%; size of powder, 100 mesh), 20 mL acrylonitrile and I mL 5% aqueous sodium hydroxide, and stirring for 12 hat room temperature. Preparation of Liquid Crystalline BoxCyanoethyl chitosan solutions of given concentration (well above critical concentration) were prepared by mixing cyanoethyl chitosan and several solvents in vials, then sealed for 7 days before use it. A liquid crystalline box used for polarized light microscopy (PLM) and SALS observation was made by putting solution between two slide glasses.(a) RES UL TS AND DISCUSSIONChitosan (/3-1 -4-linked 2-amino-2-deoxy-o-glucopyranose structural repeat units) and its derivatives show lyotropic liquid crystalline phases when dissolved in suitable solvents. 2 -5 In this study, O-cyanoethyl chitosan exhibited lyotropic liquid crystalline behavior. Fingerprint texture can be observed when O-cyanoethyl chitosan is dissolved in trifluoroacetic acid, m-cresol, formamide, N,N-dimethyl formamide, N,N-dimethyl acetamide, and dimethyl sulfoxide, showing cholesteric phase. The fingerprint texture of O-cyanoethyl chitosan was quite regular and divided into different pieces which usually differed in direction. Big pieces were few and usually isolated. This provided the possibility for SALS to measure the pitch of a single big piece of fingerprint.The SALS H., pattern of a single big piece of fingerprint (size 60 x 120 µm) prepared from 20% trifluoroacetic acid solution is shown in Figure l(b). The whole piece was within the spot of the laser beam. It was not difficult to find the corresponding fingerprint (Figure l(a)) from a few big pieces in PLM according to the special orientation.In a single piece, the periodic repeat structure behaved as a grid. So diffraction spots appeared in the direction vertical to layer planes of fingerprints in SALS pattern. Normally only the first order diffraction can be seen. From the distance d between center and diffraction spot,

Studies on the effect of substitution degree on the liquid crystalline behavior of cyanoethyl chitosan

“…Among them, cyanoethyl chitosan (CNCS) can form typical cholesteric liquid crystalline. 2,3 Previous work has reported the effect of the molecular weight of CNCS on critical liquid crystalline behaviors. 4 The present work concentrates on the effect of the degree of substitution (DS) on its liquid crystalline behaviors.…”