Development and Dynamics of Liquid Crystalline Structures Studied by Heterodyne Dynamic Light Scattering Spectroscopy

从高分子链的刚性、链动力学和分子间缔合强烈依赖于溶液中聚合物的浓度和溶剂的性质等方面考察了纤维素醋酸酯类溶致液晶聚合物从各向同性相到各向异性相的转变。在三氟乙酸(TFA)中，三醋酸酯纤维素(CTA，取代度DS=2.9)出现溶致液晶(LLC)的临界浓度v_2为24-26wt%，取代度为2.40的纤维素二乙酸酯(DS=2.40)的临界浓度v_2较高，而在去甲基乙酰胺(DMAc)中出现溶致液晶(LLC)的临界浓度v_2大于50wt%，在二甲基甲酰胺(DMAc)中未观察到溶致液晶(LLC)的出现。不同溶剂的v_2值不同，表明CTA和CDA具有特定于溶剂的分子构象。事实上，根据蠕虫链模型分析的CTA和CDA的链刚性表明，它们是Q=10和8…的半柔性链在TFA和DMAc中分别有较多的nm，在其他溶剂中有较多的柔性链。这里Q是持久长度，它表示链的刚性。对DMAc中黄麻和半稀溶液中CDA组分的动态光散射测量表明，CDA单分子与分子间缔合共存，这种缔合可能是由于葡萄糖单元中分子间C-6位OHS之间的氢键而形成的。CDA协会处于两种状态，是CDA链长度的4倍(状态II)和13-40倍(状态III)的自组装。随着CDA浓度的增加，状态II转变为状态III。此外，根据CDA集中度的不同，第三国采取了三种状态：一个长而僵硬的结构和两个巨大的结构，后者没有前者那么僵硬和长。以前的长刚体结构被认为是CDA在DMAC中形成的LLC的原型。然而，上述自组装在外场如粘性剪切场和超离心场中消失：这种缔合可能是在弱力下不能保持的暂态结构，很容易坍塌成单链。有趣的是，CDA的构象比剪切场中的构象坚硬6倍。较少

The transition from the isotropic to anisotropic phase occured in lyotropic liquid crystalline polymers such as celllulose acetates were examined in view of the polymer chain stiffness, the chain dynamics, and the intermolecular associations which depend strongly on the polymer concentration in solution and on the solvent quality. The critical concentration v_2 where the lyotropic liquid crystals (LLC) appear was 24-26wt% for cellulose triacetates (CTA,degree of substitution DS=2.9) and higher for cellulose diacetates (DS=2.40) in trifluoroacetic acid (TFA), whereas in demethylacetamide (DMAc) v_2 was more than 50wt% for CTA and 45wt% for CDA.LLC was never observed for CTA in chloroform and for CDA in dimethylformamide. The difference in v_2 with solvents indicates that CTA and CDA take a molecular conformation specific to the solvent. Indeed, the chain stiffness of CTA and CDA analyzed on the basis of the wormlike chain model revealed that they are semiflexible chains with q=10 and 8 … More nm in TFA and DMAc, respectively, and flexible chains in other solvents. Here q is the persistence length which represents the chain stiffness. Dynamic light scattering measurements for CDA fractions in DMAc in the dijute and semidilute solution regions showed that the CDA single molecule coexists with the intermolecular associations which may be formed with the hydrogen bonding between the intermolecular C-6 position OHs in the glucose unit. The CDA association was in two states, the selfassembly of four (State II) and 13-40 (State III) times as long as the single CDA chain. State II transformed to State III with increasing the CDA concentration. In addition, State III took three states, depending on the CDA concentration ; a long rigid-like structure and two huge structures, the latter being not so rigid and long as the former. The former long-rigid structure is considered to be a prototype of LLC formed by CDA in DMAc. The selfassemblies described above, however, disappeared in the external field such as the viscometric shear and the ultracentrifugal fields : the associations might be transient structures which cann't be retained under weak forces and collapse easily to a single chain. It is interesting that the CDA has a conformation six times stiffer than that in the shear field. Less