The influence of concentration on the helicoidal change of N-phthaloylchitosan (PhCh) solutions in Me2SO, DMAc and DMF was investigated by means of circular dichroism (CD). The critical concentrations to form liquid crystal phase in these three solvents were 43, 45 and 48wt%, respectively as measured with polarized optical microscope. There were two kinds of CD peaks, sharp peaks with absorption maximum at about 330nm induced by the helical conformation of molecular chain, and very broad peaks covering almost whole visible region induced by the cholesteric helix of mesophase. The later only appeared in concentrated solutions with the concentration higher than the critical concentration. The handedness of both levels of helicoidal structures changed from left-to right-handed with the increase of concentration for PhCh/Me2SO solutions. The chirality transfer occurred between these two chiral levels. For PhCh/DMAc and PhCh/DMF systems, only the handedness of helical conformation reversed, but the cholesteric helix did not change. As a method to measure critical concentration, CD is more sensitive than polarized optical microscopy (POM).

ia evaporation procss. The crystalline morphology of these films was investigated by means of ploarized optical microscopy and scanning electron microscopy. Normal spherulites with a low growth rate formed in the casting films. The different morphologies of spherulite appeared in the filims cast from the solutins with diiferent concentration. After further crystallizing for a few days, the spherulites were decorated by thousands of needlelike extended-chain crystals, which had a typical size of ～50μm(length)×2～5μm(lenght)×1～2μm(width)×1～2μm(height) in the fringe part of the spherulite. The real concentration for crystallization was dedtermined solution.

A selectively side-modified chitosan derivative, N-phthaloyl chitosan (PhthCs), was prepared. Five techniques, including circular dichroism (CD) spectropolarimetry, ultraviolet-visible (UV-vis) spectroscopy, small-angle light scattering (SALS), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), were simultaneously applied to investigate the order-disorder phase transition for the lyotropic PhthCs/dimethyl sulfoxide system. POM observations suggested that the critical concentration was 48w%, which agreed well with the DSC measurements. A four-leaf SALS picture was recorded in biphasic solutions. The four-leaf type became a circular symmetric scattering picture with a further increase in the concentration. A sharp peak at 330 nm was recorded in dilute isotropic solutions with CD measurements. The sharp peak turned into a broad tailed peak from 330 to 800nm after the phase transition occurred. The sharp peak was induced by a chromophore (phthoyl group). The broad peak was attributed to the formation of short-range-ordered organization in the concentrated solutions. In UV-vis studies, when the system varied from isotropic to anisotropic, the absorption band turned into platform. These five techniques were proven to be feasible methods for measuring the phase transition of cholesteric liquid crystals.

Two chitooligosaccharide samples (COS1 and COS2) were prepared by enzymatic degradation of chitosan. The molecular weight of the main component was determined by mass spectrometry to be 2340 and 4303, respectively. They showed cholesteric liquid crystal structures in concentrated solutions. The critical concentrations to form a lyotropic liquid crystalline phase in formic acid were measured by means of polarized optical microscopy, refractometry and Fourier transform infrared spectroscopy. The results from the three methods agreed with each other. The experimental value of COS2 was quantitatively consistent with that calculated according to Khokhlov and Semenov theory. But the experimental value of COS1 diverged from the theoretical one, which is explained by the inaccuracy at higher concentrations of the second virial approximation underlying this theory.