Fall William S, Kolli Hima Bindu, Mukherjee Biswaroop, Chakrabarti Buddhapriya
Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK.
Laboratoire de Physique des Solides - UMR 8502, CNRS, Université Paris-Saclay, 91405 Orsay, France.
Soft Matter. 2024 Oct 2;20(38):7735-7751. doi: 10.1039/d4sm01005a.
We report a simulation methodology to quantitatively predict the thermodynamic behaviour (phase diagrams) of polymer mixtures, that exhibit phases with broken orientational symmetry. Our system consists of a binary mixture of short oligomers ( = 4) and long rod-like mesogens ( = 8). Using coarse-grained molecular dynamics (CGMD) simulations we infer the topology of the temperature-dependent free energy landscape, from the probability distributions of the components for a range of compositions. The mixture exhibits nematic (N) and smectic phases (Sm-A) as a function of two temperature scales, , that governs the demixing transition, and the nematic-isotropic temperature. Thus in addition to the isotropic (I), a nematic (N) phases observed in simulations of similar systems earlier we report the formation of a new entropy-stabilized phase separated smectic-A (Sm-A) phase with alternating mesogen-rich and oligomer-rich layers. Using the mean-field free energy for polymer-dispersed liquid crystals (PDLCs), with suitably chosen parameter values, we construct a mean-field phase diagram that matches those obtained from CGMD simulations. Our results are applicable to mixtures of synthetic and biological macromolecules that undergo phase separation and are orientable, thereby giving rise to the liquid crystalline phases. Our proposed methodology has a distinct advantage over other computational techniques in its applicability to systems with complex molecular interactions and in capturing the coarsening dynamics of systems involving multiple order parameters.
我们报告了一种模拟方法，用于定量预测聚合物混合物的热力学行为（相图），该聚合物混合物呈现出具有破缺取向对称性的相。我们的系统由短低聚物（ = 4）和长棒状液晶元（ = 8）的二元混合物组成。使用粗粒化分子动力学（CGMD）模拟，我们从一系列组成的组分概率分布中推断出温度依赖的自由能景观的拓扑结构。该混合物表现出向列相（N）和近晶相（Sm-A），它们是两个温度尺度的函数， 控制着相分离转变， 是向列 - 各向同性温度。因此，除了各向同性相（I）之外，在早期类似系统的模拟中观察到的向列相（N），我们还报告了形成一种新的熵稳定相分离近晶 - A（Sm-A）相，其具有交替的富含液晶元和富含低聚物的层。使用聚合物分散液晶（PDLC） 的平均场自由能，并选择合适的参数值，我们构建了一个与从CGMD模拟获得的相图相匹配的平均场相图。我们的结果适用于经历相分离且可取向从而产生液晶相的合成和生物大分子混合物。我们提出的方法在适用于具有复杂分子相互作用的系统以及捕捉涉及多个序参量的系统的粗化动力学方面，相对于其他计算技术具有明显优势。
