How Viscous Is the Solidlike Structure at the Interface of Ionic Liquids? A Study Using Total Internal Reflection Fluorescence Spectroscopy with a Fluorescent Molecular Probe Sensitive to High Viscosity
How Viscous Is the Solidlike Structure at the Interface of Ionic Liquids? A Study Using Total Internal Reflection Fluorescence Spectroscopy with a Fluorescent Molecular Probe Sensitive to High Viscosity
复制标题
离子液体界面处的固体结构有多粘？
DOI：
10.1021/acs.langmuir.0c01528
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发表时间：
2020
期刊：
影响因子：
3.9
通讯作者：
Takahashi Hiromi
中科院分区：
文献类型：
--
作者：
Nishi Naoya;Yamazawa Takashi;Sakka Tetsuo;Hotta Hiroki;Ikeno Takayuki;Hanaoka Kenjiro;Takahashi Hiromi
为了评价离子液体界面类固体结构的粘度，采用全内反射荧光（TIRF）光谱法研究了在高粘度范围内对粘度敏感的荧光探针N，N-二乙基-N′-苯基罗丹明（Ph-DER）。用TIRF方法研究了疏水性离子液体TOMAC 4C 4 N在玻璃界面上的荧光光谱，发现Ph-DER的荧光强度随倏逝光穿透深度的减小而增强，表明界面上存在高粘度区.相比之下，甘油，这是一种分子液体，具有类似于TOMAC 4C 4 N的体积粘度，没有显示出这样的荧光增加，支持在界面处的高粘性固体状结构的形成是固有的离子液体。模型分析表明，在玻璃界面的TOMAC 4C 4 N的高粘度区域是至少两倍厚于在空气界面的离子多层膜，这意味着，固体基板增强了IL的界面结构的有序性。发现TOMAC 4C 4 N的玻璃界面处的粘度比液体本体的粘度高至少40倍。
Aiming at the evaluation of the viscosity of the interfacial solidlike structure of ionic liquids (ILs), we performed total internal reflection fluorescence (TIRF) spectroscopy forN,N-diethyl-N′-phenyl-rhodamine (Ph-DER), a fluorescent probe that is sensitive to viscosity in a high-viscosity range. TIRF spectra at the glass interface of trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide (TOMAC4C4N), a hydrophobic IL, showed that the fluorescence intensity of Ph-DER increases with the decrease of the evanescence penetration depth, suggesting that there exists a high-viscosity region at the interface. In contrast, glycerol, which is a molecular liquid with a bulk viscosity similar to that of TOMAC4C4N, did not show such a fluorescence increase, supporting that the formation of a highly viscous solidlike structure at the interface is intrinsic to ILs. A model analysis suggested that the high viscous region at the glass interface of TOMAC4C4N is at least twice thicker than the ionic multilayers at the air interface, implying that the solid substrate enhances the ordering of the interfacial structure of ILs. The viscosity at the glass interface of TOMAC4C4N was found to be at least 40 times higher than that of the liquid bulk.