Yanming Dong

Influence of degree of molar etherification on critical liquid crystal behavior of hydroxypropyl chitosan

Abstract Hydroxypropyl chitosan (HPCS) with different degree of molar etherification (DME, from 0.6 to 6.0) were synthesized and characterized by FTIR, 1H-NMR and elemental analysis. The effect of DME on critical concentration forming lyotropic liquid crystal (C*) was investigated in three solvents (formic acid, dichloroacetic acid and water). C* increased as DME raised but presented a platform at low DME (less than about 2.6), which was explained based on both the amount and the size of flexible substituents. HPCS with DME ⩾3.2 were water soluble. C* of HPCS aqueous solutions were evidently lower than those of formic acid or dichloroacetic acid solutions. Typical cholesteric texture appeared in HPCS solutions of all three solvents at proper concentrations.

Change of handedness in cholesteric liquid crystalline phase for N-phthaloylchitosan solutions in organic solvents.

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 48 wt.%, respectively as measured with polarized optical microscope. There were two kinds of CD peaks, sharp peaks with absorption maximum at about 330 nm 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).

Textures and disclinations in the cholesteric liquid‐crystalline phase of a cyanoethyl chitosan solution

Disclinations in the fingerprint-like cholesteric texture of a natural polymer derivative, cyanoethyl chitosan, were observed and studied by both polarizing optical microscopy and scanning electron microscopy. In the latter technique, permanganic etching was developed for this cholesteric texture to increase the contrast. A special mechanism for cholesteric phase etching is suggested and discussed. Some χ, λ, and τ disclinations and domain walls were observed.