Gong Xiao, Kozbial Andrew, Li Lei
Department of Chemical & Petroleum Engineering , Swanson School of Engineering , University of Pittsburgh , Pittsburgh , PA 15261 , USA.
Department of Mechanical Engineering & Materials Science , Swanson School of Engineering , University of Pittsburgh , Pittsburgh , PA 15261 , USA . Email:
Chem Sci. 2015 Jun 1;6(6):3478-3482. doi: 10.1039/c5sc00832h. Epub 2015 Apr 20.
Extended layering of ionic liquids (ILs) on the mica surface has been reported by several groups previously and it is generally accepted that the electrostatic interaction at the IL/mica interface is critical to the observed extended layering. Here we report that, indeed, water adsorption on the mica surface is the key to the extended layering of ionic liquids. The atomic force microscopy (AFM), attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR) and contact angle (CA) results show that ionic liquids form extended layering on a mica surface under ambient conditions when water is adsorbed on the mica surface under such conditions. However, when airborne hydrocarbon contaminants replace the water on the mica surface at the elevated temperatures, instead of layering, ionic liquids exhibit droplet structure, , dewetting. Based on the experimental results, we propose that water enables ion exchange between K+ and the cations of ILs on the mica surface and thus triggers the ordered packing of cations/anions in ILs, resulting in extended layering.
此前已有多个研究小组报道了离子液体（ILs）在云母表面的扩展分层现象，并且人们普遍认为IL/云母界面处的静电相互作用对于观察到的扩展分层至关重要。在此我们报告，实际上，云母表面的水吸附是离子液体扩展分层的关键。原子力显微镜（AFM）、衰减全反射傅里叶变换红外光谱（ATR-FTIR）和接触角（CA）结果表明，在环境条件下，当云母表面吸附有水时，离子液体在云母表面形成扩展分层。然而，在高温下，当空气中的碳氢化合物污染物取代云母表面的水时，离子液体呈现出液滴结构，即去湿，而不是分层。基于实验结果，我们提出水能够使云母表面的K⁺与ILs的阳离子之间发生离子交换，从而触发ILs中阳离子/阴离子的有序堆积，导致扩展分层。
