William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, Ohio 43210, USA.
Department of Mathematics and Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA.
J Chem Phys. 2023 Jun 14;158(22). doi: 10.1063/5.0152817.
Mesogens, which are typically stiff rodlike or disklike molecules, are able to self-organize into liquid crystal (LC) phases in a certain temperature range. Such mesogens, or LC groups, can be attached to polymer chains in various configurations including within the backbone (main-chain LC polymers) or at the ends of side-chains attached to the backbone in an end-on or side-on configuration (side-chain LC polymers or SCLCPs), which can display synergistic properties arising from both their LC and polymeric character. At lower temperatures, chain conformations may be significantly altered due to the mesoscale LC ordering; thus, when heated from the LC ordered state through the LC to isotropic phase transition, the chains return from a more stretched to a more random coil conformation. This can cause macroscopic shape changes, which depend significantly on the type of LC attachment and other architectural properties of the polymer. Here, to study the structure-property relationships for SCLCPs with a range of different architectures, we develop a coarse-grained model that includes torsional potentials along with LC interactions of a Gay-Berne form. We create systems of different side-chain lengths, chain stiffnesses, and LC attachment types and track their structural properties as a function of temperature. Our modeled systems indeed form a variety of well-organized mesophase structures at low temperatures, and we predict higher LC-to-isotropic transition temperatures for the end-on side-chain systems than for analogous side-on side-chain systems. Understanding these phase transitions and their dependence on polymer architecture can be useful in designing materials with reversible and controllable deformations.
介晶，通常是刚性棒状或盘状分子，能够在一定温度范围内自组织成液晶 (LC) 相。这些介晶或 LC 基团可以以各种构型附着在聚合物链上，包括在主链内（主链 LC 聚合物）或在主链上附着的侧链末端以端到端或侧到侧构型（侧链 LC 聚合物或 SCLCPs），这可以显示出源自其 LC 和聚合特性的协同特性。在较低温度下，由于介观 LC 有序，链构象可能会发生显著改变；因此，当从 LC 有序状态加热到各向同性相转变时，链从更伸展的构象返回到更随机卷曲的构象。这可能导致宏观形状变化，这在很大程度上取决于 LC 附着的类型和聚合物的其他结构特性。在这里，为了研究具有不同结构的 SCLCPs 的结构-性质关系，我们开发了一种粗粒度模型，其中包括扭转势以及 Gay-Berne 形式的 LC 相互作用。我们创建了具有不同侧链长度、链刚性和 LC 附着类型的系统，并跟踪它们的结构性质作为温度的函数。我们的模拟系统确实在低温下形成了各种组织良好的介相结构，并且我们预测端到端侧链系统的 LC 到各向同性转变温度高于类似的侧到侧侧链系统。了解这些相转变及其对聚合物结构的依赖性对于设计具有可逆和可控变形的材料可能是有用的。
