Phase Transitions in Solutions of Helical Macromolecules

由大的、伸长的分子组成的液晶， 材料科学的重要性。 的高度 在这些聚合物的溶液中获得的取向有序性可 被传递到固态。 这种额外的定向顺序 导致非常高强度的合成材料， 耐温性 这里概述的研究计划 重点关注因内部螺旋而伸长的聚合物 他们的子单位的安排。 两类聚合物， 螺旋的非常不同的原因将被研究：多肽 通过内部氢键形成螺旋结构， 单体和保持螺旋结构的多异氰酸酯 构象由于侧链相互作用。 我们会研究 渐进式灵活性的影响，通常是由 溶剂特性的变化，在这种溶液中， 大分子对相变和液晶形成的影响。 分子的取向顺序与分子链的取向顺序有关 刚度，如通过聚合物的持久长度测量的。 链刚性对液晶弹性的影响 将探索模数。 溶剂变化将在 磁场诱导液晶的凹陷， 各向同性转变温度 最后，一个独一无二的替身， 螺旋到线圈的转变，在稀溶液中的一个 将进一步描述多肽。

Liquid crystals composed of large, enlongated molecules have significance in materials science. The high degree of orientational order achieved in solutions of these polymers may be passed on to the solid state. This extra order of orientation results in synthetic materials of very high strength and temperature resistance. The research program outlined here focuses on polymers that are elongated due to an internal helical arrangement of their subunits. Two classes of polymers that are helical for very different reasons will be studied: polypeptides held in helical organization by internal hydrogen bonding among the monomers, and polyisocyanates that maintain the helical conformation due to side-chain interactions. We will examine the effects of progressive flexibility, usually brought on by variation of solvent character, in solutions of such macromolecules on phase transitions and liquid crystal formation. Molecular orientational order will be correlated with chain stiffness, as measured by the persistence length of the polymer. The influence of chain rigidity on a liquid crystal elastic modulus will be explored. Solvent variations will be examined on a magnetic filed induced depression of the liquid crystal to isotropic transition temperature. Finally, a unique double, helix-to-coil transition in dilute solution of one of the polypeptides will be further delineated.