球形膠體粒子於離子液體溶液中之擴散泳現象

Diffusiophoresis of a Single Spherical Colloidal Particle in Solutions containing Ionic Liquids

邱冠瑀(Kuan-Yu Chiu)

指導教授 ： 李克強

國立臺灣大學/工學院/化學工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202002864

摘要

本研究主要探討單一硬球於離子液體溶液中之擴散泳現象，並針對各種參數以及電泳效應驅動做了詳盡的研究。
離子液體近年來因擁有諸多優勢因此被廣泛地探討，如低蒸氣壓、高熱穩定性、低熔點、不可燃性和耐強酸等等特性，且具有極高的陰陽離子組合可能性，以上特性使離子液體可在常壓下操作並容易回收，並讓實驗過程更加安全。所以離子液體被視為具有很大潛力的綠色溶劑，在各個領域都日益受到矚目及重視。
截至目前為止，只有Khair等人針對擴散泳的離子體積效應進行討論，且他們討論的範圍為高濃度電解質溶液，也就是薄電雙層條件下的擴散泳動度解析解，並未針對稀薄溶液作探討。然而實際上大部分離子液體實驗中所使用的濃度都很稀薄，其κ大多落在0~2 nm^(-1)左右，因此我們使用數值解的方式來計算任意電雙層厚度的泳動度，解除對溶液濃度的限制，使模擬能夠更貼近現實。
我們進行了一系列的參數探討：主要的參數有三個，第一：平均離子體積分率(ν)，在考慮了離子的體積之後，擴散泳泳動度會往反方向加速，且可能泳動度反轉。第二：無因次化靜電校正長度(δ_c)，離子彼此之間的作用力增強時會增強化學泳驅動力進而加速粒子。第三：陰陽離子擴散係數差(β factor)，當陰陽離子擴散係數不同時會產生誘發電場，此電場方向視陰陽離子擴散係數差而定，且在δ_c上升時出現泳動度與預期相反之結果。綜上所述，考慮ν及δ_c可以讓我們更加貼近真實系統，進而提供更精準的預測結果。

關鍵字

擴散泳 ； 電雙層極化效應 ； 離子液體 ； 離子體積效應 ； 電荷過度遮蔽效應

並列摘要

Diffusiophoresis phenomena of a single rigid colloidal particle in ionic liquid solutions is investigated in this study.
In recent years, ionic liquids have been widely discussed because of their advantages such as low vapor pressure, high thermal stability, low melting point, incombustibility and strong acid endurance. There are numerous possible combinations of different cations and anions up to 〖10〗^18 combinations for the composition of ionic solutions, which makes ionic liquids very versatile in various practical application. Moreover, the above characteristics make it possible to operate under normal pressure and easily recovered thus safer. Therefore, ionic liquids are regarded as potential green solvents that are attracting attention in various fields.
No one has discussed diffusiophoresis of colloidal particle in a dilute ionic liquid solution. Thus we investigate this system and examine the effect of various parameters of electrokinetic interest. Among them, the mean volume fraction of ions(ν), representing the finite ion size, is found to enhance diffusiophoretic mobility in the opposite direction, and the mobility may be inverse when ion size is large. The second parameter is dimensionless electrostatic correlation length(δ_c), when the interaction of ions is not negligible, the chemiphoresis component will be strengthened accordingly with increasing δ_c. The third parameter β, the diffusivity difference factor, which appear only when the diffusivities between cation and anion are different, affect the particle motion in the direction of electrophoresis component in a way that following the sign of β. In conclusion, considering ion size and interaction between ions make the system closer to reality, thus provide more reliable prediction results.

並列關鍵字

Diffusiophoresis ； Double layer polarization ； Ionic liquid ； steric effect ； overscreening effect

參考文獻

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