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

测定了聚异氰酸己酯(PHY)和黄原胶(一种双螺旋多糖)两种硬链聚合物浓缩液的各向同性液晶界面浓度、渗透压和零剪切粘度。前者是中性聚合物，而后者是聚电解质。结果表明，所有实验数据都不能用棒状和半柔性聚合物溶液的现有理论来描述。我们修正了现有的统计力学理论，并提出了刚性链聚合物在各向同性溶液中的动力学理论，如下所述。将中性直球柱壳的定标粒子(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。计算的两个量都与实验数据进行了比较，与PHY和裂叶多糖(一种三螺旋多糖)溶液进行了比较。根据微扰理论推导了杆状和蠕虫状聚电解质溶液的亥姆霍兹自由能，其中两个聚合物之间的硬核势和静电势分别作为参考系和微扰势的对势。参考系的自由能由SP理论得到，微扰项由二次维里近似得到。黄原胶水溶液的理论与实验在相界面上的一致性基本是定量的，但在渗透压下的一致性不是很好。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。这个方程很好地描述了在很宽的C和M范围内，黄原胶和裂叶聚糖各向同性溶液的零剪切粘度与聚合物浓度C和相对分子质量M的关系。

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.