Electrowetting of ionic liquids under high vacuum conditions
Electrowetting of ionic liquids under high vacuum conditions
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DOI：
10.1524/zpch.2008.222.1.117
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发表时间：
2008-01-01
影响因子：
2.5
通讯作者：
Freyland, W.
中科院分区：
文献类型：
--
作者：
Halka, V.;Freyland, W.
两种咪唑鎓基离子液体[C（4）mim[PF 6]和[C（6）mim][NTf 2]在不同介电基底SiO2-Si和环氧化物-Cu上的电润湿，在不同的温度和液滴半径R = 1-为了避免吸附的薄液体膜对接触角测量的影响并解决离子液体在高施加电压下可能的分解，我们进行了首次报道了超高真空条件下的电润湿实验。两种离子液体在两种基板上的电润湿曲线表现出对称的抛物线形状作为所施加的直流电压的函数。然而，与水性和有机电解质相比，在接触角的较低变化下达到饱和。在饱和时，通过形成大气泡观察到离子液体的明显分解。据推测，这是由电击穿和相应的放电引起的。分解产物可以强烈地影响液滴的界面张力，这解释了类似于15度的显著接触角滞后。测量的电润湿曲线的温度依赖性基本上是由根据经典的Young-Lippmann方程的液体/蒸气界面张力确定的。通过修改的Young方程对电润湿曲线的液滴尺寸依赖性的解释产生类似于10（-5）N的表观线张力，其在量值上与有机液体相当。
Electrowetting of two imidazolium based ionic liquids, [C(4)mim[PF6] and [C(6)mim][NTf2], on different dielectric substrates, SiO2-Si and epoxide-Cu, has been studied at various temperatures and droplet radii R = 1-3 mm. To avoid the effect of adsorbed thin liquid films on the contact angle measurements and to resolve possible decomposition of the ionic liquids at high applied voltages we have performed the electrowetting experiments under ultra high vacuum conditions which is reported here for the first time. The electrowetting curves of both ionic liquids on both substrates exhibit a symmetrical, parabolic shape as a function of the applied dc-voltage. However, in comparison with aqueous and organic electrolytes saturation is reached at a lower variation of the contact angle. At saturation a clear decomposition of the ionic liquids sets in which is observed by the formation of large bubbles. Presumably, this is caused by electrical breakdown and the corresponding discharging. The decomposition products can strongly affect the interfacial tensions of the droplets what explains a pronounced contact angle hysteresis of similar to 15 degrees. The measured temperature dependence of the electrowetting curves is essentially determined by that of the liquid/vapor interfacial tension in accordance with the classical Young-Lippmann equation. Interpretation of the droplet size dependence of the electrowetting curves by the modified Young equation yields an apparent line tension of similar to 10(-5) N, which is comparable in magnitude to organic liquids.