摘要
本工作利用模拟体系内偶极分子偶极矩不同来描述组分间介电差异,采用分子动力学模拟方法对含有离子的简单液体体系、液体混合体系和高分子溶液体系平衡态性质进行一系列的模拟研究,考察离子周围的偶极子重组效应对体系结构变化和平衡态性质的影响。我们的研究结果从微观角度证明了SCFT理论关于离子周围富集较大偶极矩溶剂分子结论的正确性[1]。重点研究了单组分聚合物、共混均聚物和嵌段共聚物体系内的离子溶剂化能,揭示了几种体系内溶剂化能呈现出明显的链长依赖关系。强调由于高分子的连接性影响离子周围偶极重组,导致单组分聚合物体系内不同偶极矩时离子溶剂化能呈现不同的链长依赖关系。对于共混均聚物和嵌段共聚物体系,溶剂化能对链长的依赖关系与体系内两种溶剂偶极矩选取密切相关。当两种溶剂分子均选取较小的偶极矩时,离子与偶极子间的关联较弱,随着链长的增加,得到与由自洽场理论定性一致的结果[2];当选取的偶极矩令离子与偶极子间的关联较强时,得到与由自洽场理论定性相反的结果。并阐述了由于拓扑结构不同而导致离子在共混均聚物和嵌段共聚物体系内溶剂化能的差异。我们的研究结果将进一步推动理论工作的发展。
We study the ion solvation in the single-component polymers,block copolymer melts,and polymer blends using molecular dynamics simulations.In our simulations,polymers are formed through the connection of beads that provide the dielectric response.We demonstrate the local enrichment of higher-dielectric components near ions,which corresponds well with the result of mean-field theories[1].Moreover,the chain connectivity significantly affects the reorientation of molecular dipoles in response to the electrostatic field from ions.Thus,we illustrate the marked difference in the solvation energy between the block copolymer and polymer blend.Importantly,the solvation energy substantially depends on the chain length of the polymers,in stark contrast to the Born solvation energy.Interestingly,we observe the different dependence of solvation energy on the chain length for various dipole moments in the single-component polymers.We also show that our simulation results exhibit striking similarity to the result of the recent self-consistent mean field theories[2].However,for strongly correlated dipoles and ions,our simulations provide qualitatively opposite behaviors to these results,suggesting further development of the theoretical frameworks.
引文
[1]Z.-G.Wang,J.Phys.Chem.B 2008,112:16205-16213
[2]I.Nakamura,J.Phys.Chem.B 2014,10:5787-5797