硬球半柔性聚合物致密堆积中的局部和全局秩序

Local and Global Order in Dense Packings of Semi-Flexible Polymers of Hard Spheres.

作者信息

Martínez-Fernández Daniel, Herranz Miguel, Foteinopoulou Katerina, Karayiannis Nikos Ch, Laso Manuel

机构信息

Institute for Optoelectronic Systems and Microtechnology (ISOM) and Escuela Técnica Superior de Ingenieros Industriales (ETSII), Universidad Politécnica de Madrid (UPM), José Gutiérrez Abascal 2, 28006 Madrid, Spain.

出版信息

Polymers (Basel). 2023 Jan 20;15(3):551. doi: 10.3390/polym15030551.

Abstract

The local and global order in dense packings of linear, semi-flexible polymers of tangent hard spheres are studied by employing extensive Monte Carlo simulations at increasing volume fractions. The chain stiffness is controlled by a tunable harmonic potential for the bending angle, whose intensity dictates the rigidity of the polymer backbone as a function of the bending constant and equilibrium angle. The studied angles range between acute and obtuse ones, reaching the limit of rod-like polymers. We analyze how the packing density and chain stiffness affect the chains' ability to self-organize at the local and global levels. The former corresponds to crystallinity, as quantified by the Characteristic Crystallographic Element (CCE) norm descriptor, while the latter is computed through the scalar orientational order parameter. In all cases, we identify the critical volume fraction for the phase transition and gauge the established crystal morphologies, developing a complete phase diagram as a function of packing density and equilibrium bending angle. A plethora of structures are obtained, ranging between random hexagonal closed packed morphologies of mixed character and almost perfect face centered cubic (FCC) and hexagonal close-packed (HCP) crystals at the level of monomers, and nematic mesophases, with prolate and oblate mesogens at the level of chains. For rod-like chains, a delay is observed between the establishment of the long-range nematic order and crystallization as a function of the packing density, while for right-angle chains, both transitions are synchronized. A comparison is also provided against the analogous packings of monomeric and fully flexible chains of hard spheres.

摘要

通过在不断增加的体积分数下进行广泛的蒙特卡罗模拟,研究了线性半柔性聚合物(其链节为相切硬球)致密堆积中的局部和全局有序性。链的刚度由一个用于控制弯曲角度的可调谐谐振势来控制,该势的强度根据弯曲常数和平衡角决定了聚合物主链的刚性。所研究的角度范围在锐角和钝角之间,直至达到棒状聚合物的极限。我们分析了堆积密度和链刚度如何影响链在局部和全局层面上的自组织能力。前者对应于结晶度,通过特征晶体学元素(CCE)范数描述符进行量化,而后者则通过标量取向序参量来计算。在所有情况下,我们确定了相变的临界体积分数,并测量了已形成的晶体形态,绘制了作为堆积密度和平衡弯曲角函数的完整相图。获得了大量的结构,从具有混合特征的随机六方密堆积形态,到单体水平上几乎完美的面心立方(FCC)和六方密堆积(HCP)晶体,以及链水平上具有长轴和短轴液晶元的向列相中间相。对于棒状链,观察到随着堆积密度的变化,长程向列序的建立和结晶之间存在延迟,而对于直角链,两种转变是同步的。还与硬球单体和完全柔性链的类似堆积进行了比较。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/180b/9919756/90e1396da607/polymers-15-00551-g001.jpg

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