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质子离子液体(PILs)的纳米结构和物理化学性质:用于PILs制备和性质筛选的高通量方法的开发

Protic ionic liquids (PILs) nanostructure and physicochemical properties: development of high-throughput methodology for PIL creation and property screens.

作者信息

Greaves Tamar L, Ha Krystal, Muir Benjamin W, Howard Shaun C, Weerawardena Asoka, Kirby Nigel, Drummond Calum J

机构信息

School of Applied Sciences, College of Science, Engineering and Health, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia.

出版信息

Phys Chem Chem Phys. 2015 Jan 28;17(4):2357-65. doi: 10.1039/c4cp04241g. Epub 2014 Dec 5.

Abstract

A high-throughput approach was developed in order to prepare and dry a series of protic ionic liquids (PILs) from 48 Brønsted acid-base combinations. Many combinations comprised an alkyl carboxylic acid paired with an alkyl amine. Visual screens were developed to identify which acid-base combinations formed PILs, and of those, which PILs were likely to have high surface tensions, low viscosities, and low melting points. The surface tension screen was validated through pendant drop surface tension measurements. Karl Fischer coulometric titration was used to obtain the water contents, and it was noted that there is a considerable difference in the drying rate throughout this series of PILs. It was observed that an octyl chain present on either the cation or anion was detrimental to the formation of a PIL with a low melting point, and instead increased the likelihood of a gel or solid forming. The nanostructure of the PILs was determined, using synchrotron small and wide angle X-ray scattering (SAXS/WAXS), to consist of polar and non-polar domains, with the alkyl chains on the cation and anion intercalating. The results indicate that both the alkyl chain on the cation and/or anion contribute to the correlation distance, for the intermediate range order, with the expectation that there is charge alternation of the ions in the polar region. The maximum correlation distance was observed when there was an alkyl chain present on only one ion. This correlation distance could be significantly reduced by varying the alkyl chain length present on the other ion, which was attributed to increased disorder and interdigitation of chains, and to toe-to-toe alignment of the chains. To the best of our knowledge this is the first PIL report into the effect of having an alkyl chain present on both the cation and the anion.

摘要

为了从48种布朗斯特酸碱组合制备并干燥一系列质子离子液体(PILs),开发了一种高通量方法。许多组合包括烷基羧酸与烷基胺配对。开发了视觉筛选方法来确定哪些酸碱组合形成了PILs,以及其中哪些PILs可能具有高表面张力、低粘度和低熔点。通过悬滴表面张力测量验证了表面张力筛选方法。使用卡尔费休库仑滴定法获得水含量,并注意到在这一系列PILs中干燥速率存在相当大的差异。观察到阳离子或阴离子上存在的辛基链不利于低熔点PIL的形成,反而增加了形成凝胶或固体的可能性。使用同步加速器小角和广角X射线散射(SAXS/WAXS)确定了PILs的纳米结构,其由极性和非极性域组成,阳离子和阴离子上的烷基链相互嵌入。结果表明,阳离子和/或阴离子上的烷基链都对中间范围有序的相关距离有贡献,预计极性区域中离子存在电荷交替。当仅一个离子上存在烷基链时观察到最大相关距离。通过改变另一个离子上存在的烷基链长度,可以显著减小这种相关距离,这归因于链的无序增加和相互交错,以及链的头对头排列。据我们所知,这是第一份关于阳离子和阴离子上都存在烷基链的影响的PIL报告。

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