Department of Chemical Engineering, Laboratory for Advanced Materials, Tsinghua University, Beijing, People's Republic of China.
J Chem Phys. 2011 Dec 28;135(24):244901. doi: 10.1063/1.3671451.
The phase behavior of lyotropic rigid-chain liquid crystal polymer was studied by dissipative particle dynamics (DPD) with variations of the solution concentration and temperature. A chain of fused DPD particles was used to represent each mesogenic polymer backbone surrounded with the strongly interacted solvent molecules. The free solvent molecules were modeled as independent DPD particles, where each particle includes a lump of solvent molecules with the volume roughly equal to the solvated polymer segment. The simulation shows that smectic-B (S(B)), smectic-A (S(A)), nematic (N), and isotropic (I) phases exist within certain regions in the temperature and concentration parameter space. The temperature-dependent S(B)∕S(A), S(A)∕N, and N∕I phase transitions occur in the high concentration range. In the intermediate concentration range, the simulation shows coexistence of the anisotropic phases and isotropic phase, where the anisotropic phases can be the S(B), S(A), or N phases. Mole fraction and compositions of the coexisted phases are determined from the simulation, which indicates that concentration of rigid rods in isotropic phase increases as the temperature increases. By fitting the orientational distribution function of the systems, the biphasic coexistence is further confirmed. From the parameter α obtained for the simulation, the distribution of the rigid rods in the two coexistence phases is quantitatively evaluated. By using model and simulation methods developed in this work, the phase diagrams of the lyotropic rigid-chain polymer liquid crystal are obtained. Incorporating the solvent particles in the DPD simulation is critical to predict the phase coexistence and obtain the phase diagrams.
溶致刚性链液晶聚合物的相行为通过耗散粒子动力学（DPD）进行了研究，其变化取决于溶液浓度和温度。使用融合的 DPD 粒子链来表示每个介晶聚合物主链，周围环绕着强烈相互作用的溶剂分子。自由溶剂分子被建模为独立的 DPD 粒子，其中每个粒子包括一团溶剂分子，其体积大致等于溶剂化聚合物段。模拟表明，在温度和浓度参数空间的某些区域内存在层状-B（S(B)）、层状-A（S(A)）、向列（N）和各向同性（I）相。在高浓度范围内发生温度依赖性的 S(B)∕S(A)、S(A)∕N 和 N∕I 相转变。在中间浓度范围内，模拟显示各向异性相和各向同性相共存，其中各向异性相可以是 S(B)、S(A)或 N 相。通过模拟确定共存相的摩尔分数和组成，表明各向同性相中刚性棒的浓度随温度升高而增加。通过拟合系统的取向分布函数，进一步证实了双相共存。从模拟中获得的参数α定量评估了两个共存相中的刚性棒的分布。通过使用本文开发的模型和模拟方法，获得了溶致刚性链聚合物液晶的相图。在 DPD 模拟中包含溶剂粒子对于预测相共存和获得相图至关重要。
