Study on Concentrated Solutions of Stiff-Chain Polymers : Thermodynamic and Viscoelastic Properties

测定了两种硬链聚合物——聚异氰酸己酯（PHIC）和黄原胶（双螺旋多糖）的浓溶液的各向同性-液晶相边界浓度、渗透压和零剪切粘度。前者为中性聚合物，后者为聚电解质。结果表明，对于棒状和半柔性聚合物溶液，所有的实验数据都不能用现有的理论来描述。我们修正了现有的统计力学理论，并提出了一种新的各向同性溶液中硬链聚合物的动力学理论，如下所述。将Cotter的中性直球形柱体的尺度粒子（SP）理论推广到半柔性聚合物溶液中，计算了溶液的各向同性-液晶相界和渗透压。计算的两个量与实验数据进行了比较，结果与实验结果一致。从微扰理论出发，推导了棒状和蠕虫状聚电解质溶液的亥姆霍兹自由能，其中两种聚合物之间的硬核电位和静电电位分别作为参考体系和微扰的对电位。参考系统的自由能由SP理论得到，微扰项由二次维里近似求得。水黄原胶的理论与实验结果在相界上基本一致，但在渗透压上不太一致。用“模糊圆柱体”模型代替刚性链，建立了刚性链聚合物溶液浓度稀释的粘度方程。该方程很好地描述了各向同性黄原胶和裂叶菌溶液在很宽的C和M范围内的零剪切粘度对聚合物浓度C和分子量M的依赖关系。

The isotropic-liquid crystal phase boundary concentrations, osmotic pressure, and zero-shear viscosity were measured for concentrated solutions of two stiff-chain polymers, poly (hexyl isocyanate) (PHIC) and xanthan, a double-helical polysaccharide. The former is a neutral polymer, while the latter is a polyelectrolyte. It turned out that all the experimental data obtained cannot be described by current theories for rod-like and semi-flexible polymer solutions. We modified the current statistical-mechanical theories and also proposed a new dynamic theory of stiff-chain polymers in isotropic solution as described below.1. The scaled particle (SP) theory of Cotter for neutral straight spherocylinders was extended to semiflexible polymer solutions to calculate the isotropic-liquid crystal phase boundaries and osmotic pressure of the solution. Both quantities calculated were compared favorably with the experimental data PHIC and schizophyllan (a triple helical polysaccharide) solutions.2. The Helmholtz free energy of rod-like and worm-like polyelectrolyte solutions was formulated from a perturbation theory, where the hard core and electrostatic potentials between two polymers were taken as the pair potentials of the reference system and the perturbation, respectively. The free energy of the reference system was obtained from the SP theory, while the perturbation terms were evaluated by the second virial approximation. The agreement between theory and experiment of aqueous xanthan was almost quantitative in the phase boundaries, but not good in osmotic pressure.3. A viscosity equation for stiff-chain polymer solutions dilution through concentration was formulated by replacing the stiff chain by the "fuzzy cylinder" model. This equation describe well the dependence of the zero-shear viscosity on polymer concentration C and molecular weight M for isotropic soltions of xanthan and schizophyllan over wide ranges of C and M.