Sommermann D, Köhler W
Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany.
J Chem Phys. 2023 Oct 28;159(16). doi: 10.1063/5.0176432.
We have studied diffusion and thermodiffusion in the ternary system polystyrene + toluene + cyclohexane over the entire composition range of the binary solvent toluene + cyclohexane and for polymer concentrations up to 0.1 mass fractions by multi-color optical beam deflection. The polystyrene molar masses were 4.88 and 17.90 kg/mol. The inversion problem of the contrast factor matrix could be avoided by reasonable a priori assumptions about the diffusion eigenvectors. The fast mode of the bimodal dynamics is attributed to the interdiffusion of the two solvents at constant polymer concentration, whereas the slow mode is due to the diffusion of the polymer with respect to the binary solvent. The amplitude of the fast mode vanishes in the pure toluene and the pure cyclohexane limits of the mixed solvent. The amplitude of the slow mode increases with polymer concentration. The composition and temperature dependence of the slow diffusion eigenvalue, the hydrodynamic correlation length, and the Soret coefficient of the polymer reflect the transition from a good to a theta solvent with increasing cyclohexane content and with decreasing temperature. Due to cross diffusion, cyclohexane reverses its migration direction between the fast and the slow mode, leading to a positive thermodiffusion but a negative Soret coefficient. The polymer thermodiffusion coefficients during the slow mode vary by approximately a factor of two, depending on the solvent composition. Rescaling with the solvent viscosity collapses all data onto a single master curve with an extrapolated value of ηDT ≈ 6 × 10-15 Pa m2 K-1 in the dilute limit. This value is well known from various other binary polymer/solvent mixtures.
我们通过多色光束偏转法研究了三元体系聚苯乙烯+甲苯+环己烷在二元溶剂甲苯+环己烷的整个组成范围内以及聚合物浓度高达0.1质量分数时的扩散和热扩散。聚苯乙烯的摩尔质量分别为4.88和17.90 kg/mol。通过对扩散特征向量进行合理的先验假设，可以避免对比度因子矩阵的反演问题。双峰动力学的快速模式归因于在聚合物浓度恒定的情况下两种溶剂的相互扩散，而慢速模式则是由于聚合物相对于二元溶剂的扩散。快速模式的振幅在混合溶剂的纯甲苯和纯环己烷极限中消失。慢速模式的振幅随聚合物浓度增加。聚合物的慢速扩散特征值、流体动力学相关长度和索雷特系数的组成和温度依赖性反映了随着环己烷含量增加和温度降低，从良溶剂到θ溶剂的转变。由于交叉扩散，环己烷在快速和慢速模式之间反转其迁移方向，导致正的热扩散但负的索雷特系数。慢速模式下的聚合物热扩散系数根据溶剂组成变化约两倍。用溶剂粘度进行重新标度可将所有数据合并到一条单一的主曲线上，在稀溶液极限下外推值为ηDT≈6×10-15 Pa m2 K-1。这个值在各种其他二元聚合物/溶剂混合物中是众所周知的。
