Thermotropic phase transition of liquid crystalline solution of chitosan/dichloroacetic acid

The thermotropic phase transition of liquid crystalline solution of chitosa n/dichloroacetic acid (DCA) was studied by means of DSC. When the polymer c oncentration c, was higher than the critical one, c*, an clear endothermal peak attributed to the anisotropic-isotrdpic phase transition of chitosan s olution was observed on DSC heating trace. The exothermal peak was obviousl y observed on DSC trace upon cooling from above the "clearing" temperature because of the reverse phase transition. It was found that the lyotropic so lution of chitosan/DCA can exhibit thermotropic behavior and the liquid cry stalline phase formation in solution is also nucleation-controlled. Similar to the crystalline polymer, the thermotropic phase transition for liquid c rystalline solution of chitosan/dichloroacetic acid is influenced by histor y of the liquid crystalline phase formation. In addition, the thermotropic phase transition was verified by the polarized light microscopy observation as well as by the changes of depolarizing transmittance intensity as the f unction of temperature.