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非全取代的乙基纤维素在浓硫酸催化下与醋酸反应,生成乙基醋酸纤维素。乙基醋酸纤维素在适当的条件下可以形成溶致性液晶。随浓度的升高,溶液从各向同性态经两相共存,转变成完全的液晶态。在加热溶液时,可以看到两相共存状态的形成和液晶相的完全消失,降低温度,液晶相又可以再生成。在液晶相生成的过程中,存在过冷现象,液晶聚集的区域由许多微小的取向区域组成,它们的取向方向不相同。溶液的n—c曲线在各相同性、两相共存和液晶态区域内是直线,但在这些相态之间相互转变时出现转折点。溶液的双折射△n=ne—no在两相共存与液晶态相互转变时也会发生较大变化。乙基醋酸纤维素大分子链的刚性随有机酸溶剂体系的酸的强度增大而增大,使临界浓度C_1~*随溶剂酸的强度的增大而减小。
Unsaturated ethyl cellulose reacts with acetic acid under concentrated sulfuric acid catalysis to produce ethyl cellulose acetate. Ethyl cellulose acetate can form lyotropic liquid crystals under appropriate conditions. With the increase of concentration, the solution coexists from the isotropic state to the complete liquid crystal state. When the solution is heated, it can be seen that the two phases coexist and the liquid phase disappears completely, the temperature is lowered and the liquid crystal phase regenerates. In the process of liquid crystal phase generation, there is a phenomenon of subcooling, and the area where the liquid crystal is accumulated is composed of many minute alignment regions, and their orientation directions are different. The n-c curve of the solution is linear in the regions of the same identity, two phases coexistence and the liquid crystal state, but a turning point occurs when the phases transition from each other. The birefringence of the solution Δn = ne-no also changes greatly when the two phases coexist and the liquid crystal phase changes each other. The rigidity of the ethyl cellulose acetate macromolecule chains increases with the increase of the acid strength of the organic acid solvent system, so that the critical concentration C_1 ~ * decreases with the increase of the strength of the solvent acid.