Au(111)-离子液体界面层状结构与温度关联的原位AFM力曲线研究

本文针对BMIPF6 和OMIPF6两种离子液体，在电极表面远离零电荷电位且以负电荷表面电位下，运用AFM力曲线详细地研究了其与Au(111)单晶电极界面所形成的层状结构与温度的关联. 在15 ~ 40 ^oC的温度范围内，温度越低其离子液体层状结构越稳定. 温度对OMIPF₆离子液体层状结构的稳定性和数目的影响较BMIPF₆缓和：温度变化5 ^oC，OMIPF₆靠近表面第一层层状结构的力值变化仅为1 ~ 2 nN，而BMIPF6第一层层状结构的力值变化为3 ~ 5 nN；较低温下，BMIPF₆中层状结构的数目有所增加，而OMIPF₆的层状数目始终保持两层，且随温度的变化并不敏感. 这可归因于两种离子液体的阳离子尺寸以及与电极表面的作用方式和强度不同；同时，OMIPF₆较粘稠，其热运动受温度的影响不甚敏感.

In-Situ AFM Force Curve Investigations on Layered Structures of Au(111)-Ionic Liquid Interfaces and Temperature Dependence

By utilizing in-situ AFM force curve measurements systematic investigations have been carried out on Au(111)-ionic liquid interface in BMIPF₆ and OMIPF₆ of imidazolium-based ionic liquids with different lengths of alkyl side chains. The temperature dependence of the number, thickness and stability of the layered structures of each system are studied by performing AFM force curve measurements at potentials far negative of the PZC. The layered structures at Au (111)/BMIPF₆ interface are composed of two charged interior layers and two neutral exterior layers at -1.0 V, while those at Au (111)/OMIPF₆ interface only one charged interior layer and one neutral exterior layer at -16 V. But there contains only one neutral exterior layer and one charged interior layer. Temperature influence on the layering behaviors of the two kinds of ionic liquid systems is investigated. It is shown that within the temperature range of 15 to 40 ^oC, the stability of the layered structures in both BMI⁺ and OMI⁺ systems increases as temperature decreases because of the reduced thermal perturbation. However, the temperature influence is greater for BMI⁺ than for OMI⁺ system. Variation of temperature by 5 ^oC, the rupture force of the first layer in OMIPF₆ changes only 1 ~ 2 nN at -1.6 V, while that in BMIPF6 changes 1 ~ 6 nN at -1.0 V. In addition, at low temperatures, the number of the BMIPF₆ layered structures increase, while that of OMIPF₆ layer structure maintains the same. This difference may be associated with the different molecular sizes that lead to different intermolecular interactions and interactions between the molecule and electrode surface. Meanwhile, OMIPF₆ is more viscous than BMIPF₆ so that the former could be less sensitive to temperature perturbation.