Metastable State during Melting and Solid-Solid Phase Transition of [C&ITn&ITMim][NO3] (&ITn&IT=4-12) Ionic Liquids by Molecular Dynamics Simulation

doi:10.1021/acs.jpcb.7b09073

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	Metastable State during Melting and Solid-Solid Phase Transition of [C&ITn&ITMim][NO3] (&ITn&IT=4-12) Ionic Liquids by Molecular Dynamics Simulation
	Cao, WD ; Wang, YT; Saielli, G 2
刊名	JOURNAL OF PHYSICAL CHEMISTRY B
	2018
卷号	122 期号:1 页码:229-239
关键词	HEXAFLUOROPHOSPHATE SALTS CHAIN-LENGTH FORCE-FIELD CRYSTALS BEHAVIOR DIFFUSION INSIGHTS SYSTEMS
ISSN号	1520-6106
DOI	10.1021/acs.jpcb.7b09073
英文摘要	We simulate the heating process of ionic liquids [C(n)Mim][NO3] (n = 4, 6, 8, 10, 12), abbreviated as C-n, by means of molecular dynamics (MD) simulation starting from a manually constructed triclinic crystal structure composed of polar layers containing anions and cationic head groups and nonpolar regions in between containing cationic alkyl side chains. During the heating process starting from 200 K, each system undergoes first a solid-solid phase transition at a lower temperature, and then a melting phase transition at a higher temperature to an isotropic liquid state (C-4, C-6, and C-8) or to a liquid crystal state (C-10 and C-12). After the solid-solid phase transition, all systems keep the triclinic space symmetry, but have a different set of lattice constants. C-4 has a mote significant structural change in the nonpolar regions which narrows the layer spacing, while the layer spacings of other system change little, which can be qualitatively understood by considering that the contribution of the effective van der Waals interaction in the nonpolar regions (abbreviated as EF1) to free energy becomes stronger with increasing side-chain length, and at the same time the contribution of the effective electrostatic interaction in the polar layers (abbreviated as EF2) to free energy remains almost the same. The melting phase transitions of, all systems except C-6 are found to be a two-step process with an intermediate metastable state appeared during the melting from the crystal state to the liquid or liquid crystal state. Because the contribution of EF2 to the free energy is larger than EF1, the metastable state of C-4 has the feature of having higher ordered polar layers and lower ordered side-chain orientation. By contrast, C-8-C-1, have the feature of having lower ordered polar layers and higher ordered side-chain orientation, because for these systems, the contribution of EF2 to the free energy is smaller than EF1. No metastable state is found for C-6 because the free-energy contribution of EF1 is balanced with EF2.
学科主题	Chemistry
语种	英语
内容类型	期刊论文
源URL	[http://ir.itp.ac.cn/handle/311006/22983]
专题	理论物理研究所_理论物理所1978-2010年知识产出
作者单位	1.Chinese Acad Sci, Inst Theoret Phys, CAS Key Lab Theoret Phys, 55 East Zhongguancun Rd,POB 2735, Beijing 100190, Peoples R China 2.Univ Chinese Acad Sci, Sch Phys Sci, 19A Yuquan Rd, Beijing 100049, Peoples R China 3.CNR, Unit Padova, Inst Membrane Technol, Via Marzolo 1, I-35131 Padua, Italy
推荐引用方式 GB/T 7714	Cao, WD,Wang, YT,Saielli, G. Metastable State during Melting and Solid-Solid Phase Transition of [C&ITn&ITMim][NO3] (&ITn&IT=4-12) Ionic Liquids by Molecular Dynamics Simulation[J]. JOURNAL OF PHYSICAL CHEMISTRY B,2018,122(1):229-239.
APA	Cao, WD,Wang, YT,&Saielli, G.(2018).Metastable State during Melting and Solid-Solid Phase Transition of [C&ITn&ITMim][NO3] (&ITn&IT=4-12) Ionic Liquids by Molecular Dynamics Simulation.JOURNAL OF PHYSICAL CHEMISTRY B,122(1),229-239.
MLA	Cao, WD,et al."Metastable State during Melting and Solid-Solid Phase Transition of [C&ITn&ITMim][NO3] (&ITn&IT=4-12) Ionic Liquids by Molecular Dynamics Simulation".JOURNAL OF PHYSICAL CHEMISTRY B 122.1(2018):229-239.