Drastic Phase Transition in Ionic Liquid [Dmim][Cl] Confined Between Graphite Walls: New Phase Formation

• Published in: Journal of physical chemistry. C 2009-03, Vol.113 (11), p.4618-4622
• Main Authors: Sha, Maolin, Wu, Guozhong, Liu, Yusheng, Tang, Zhongfeng, Fang, Haiping
• Format: Article
• Language: English
• Subjects: C: Surfaces, Interfaces, Catalysis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp810980v

Confinement can induce unusual behavior in the properties of matter. Using atomistic molecular dynamics simulations, we report here a liquid-to-solid transition of a bilayer of ionic liquid 1,3-dimethylimidazolium chloride ([Dmim][Cl]) confined between graphite walls in order to mimic the phase transition of an ionic liquid confined to hydrophobic nanospace. It was found that the ionic liquid bilayer undergoes a clear and drastic phase transition at a wall distance of about 1.1 nm, forming a new high-melting-point solid phase with different hydrogen bonding networks. In the new phase, each cation is surrounded by the three nearest-neighbor anions, and each anion is also encircled by the three nearest-neighbor cations. Strong π−π stacking interactions are found between the cations of the bilayer solid. The anions can be formed into a hexagonal ring around the cations. The new bilayer solid is a high-melting-point crystal possessing a melting point of 825−850 K, which is higher than that of the bulk crystal by more than 400 K.