Department of Chemical and Biomolecular Engineering, Colburn Laboratory, University of Delaware, 150 Academy Street, Newark, DE 19716, USA.
Soft Matter. 2018 Jan 17;14(3):411-423. doi: 10.1039/c7sm02199b.
In this paper, we apply molecular simulation and liquid state theory to uncover the structure and thermodynamics of homopolymer blends of the same chemistry and varying chain architecture in the presence of explicit solvent species. We use hybrid Monte Carlo (MC)/molecular dynamics (MD) simulations in the Gibbs ensemble to study the swelling of ∼12 000 g mol linear, cyclic, and 4-arm star polystyrene chains in toluene. Our simulations show that the macroscopic swelling response is indistinguishable between the various architectures and matches published experimental data for the solvent annealing of linear polystyrene by toluene vapor. We then use standard MD simulations in the NPT ensemble along with polymer reference interaction site model (PRISM) theory to calculate effective polymer-solvent and polymer-polymer Flory-Huggins interaction parameters (χ) in these systems. As seen in the macroscopic swelling results, there are no significant differences in the polymer-solvent and polymer-polymer χ between the various architectures. Despite similar macroscopic swelling and effective interaction parameters between various architectures, the pair correlation function between chain centers-of-mass indicates stronger correlations between cyclic or star chains in the linear-cyclic blends and linear-star blends, compared to linear chain-linear chain correlations. Furthermore, we note striking similarities in the chain-level correlations and the radius of gyration of cyclic and 4-arm star architectures of identical molecular weight. Our results indicate that the cyclic and star chains are 'smaller' and 'harder' than their linear counterparts, and through comparison with MD simulations of blends of soft spheres with varying hardness and size we suggest that these macromolecular characteristics are the source of the stronger cyclic-cyclic and star-star correlations.
在本文中,我们应用分子模拟和液态理论,揭示了同种化学组成但链结构不同的均聚物共混物在明确溶剂物种存在下的结构和热力学性质。我们使用吉布斯系综中的混合蒙特卡罗(MC)/分子动力学(MD)模拟来研究约 12000 g/mol 的线性、环状和 4 臂星形聚苯乙烯链在甲苯中的溶胀。我们的模拟表明,各种结构之间的宏观溶胀响应没有明显区别,并且与线性聚苯乙烯通过甲苯蒸气溶剂退火的已发表实验数据相匹配。然后,我们使用 NPT 系综中的标准 MD 模拟以及聚合物参考相互作用位点模型(PRISM)理论,计算这些体系中的有效聚合物-溶剂和聚合物-聚合物 Flory-Huggins 相互作用参数(χ)。正如在宏观溶胀结果中看到的,各种结构之间的聚合物-溶剂和聚合物-聚合物 χ 没有显著差异。尽管各种结构之间的宏观溶胀和有效相互作用参数相似,但链质心之间的对关联函数表明,环状或星形链在线性-环状共混物和线性-星形共混物中的相互作用比线性链-线性链相互作用更强。此外,我们注意到相同分子量的环状和 4 臂星形结构的链级关联和回转半径之间存在惊人的相似之处。我们的结果表明,环状和星形链比它们的线性对应物更小且更硬,并且通过与具有不同硬度和尺寸的软球混合物的 MD 模拟进行比较,我们认为这些高分子特性是环状-环状和星-星相互作用更强的原因。