液滴於電解質溶液中之介電泳現象

電動力學現象現今已廣泛出現於微流體裝置(microfluidic)、生醫材料、實驗室晶片(lab-on-a-chip)等應用。其中，利用不均勻電場操控介電質運動的「介電泳」(dielectrophoresis, DEP)，是較為新穎且具發展潛力的技術，然而相對應的理論研究仍為數不多且有所限制。此外真實介電泳系統中存在多種非傳統硬球型態的粒子，如液滴與生物細胞等，無法以硬球模型模擬之。因此吾人欲突破傳統的設限，針對上述特殊結構之膠體粒子做前瞻性的研究。　　本文的研究目標是影響介電泳作用力的關鍵因子─dipole coefficient，其代表粒子在介質中的有效極化程度。吾人使用電動力學模型來描述電解質溶液中帶電的液滴粒子，研究其周圍電雙層與外加電場的交互作用，以及有效偶極矩在不同操作條件下的變化。本研究主要探討的參數為：電雙層厚度、液滴表面帶電量、液滴與介質黏度、介電常數、外加交流電場頻率等。　　液滴在電場下的電泳運動，影響電雙層內離子分布，也影響dipole coefficient與有效偶極矩強度。從結果中發現，液滴表面帶電量與dipole coefficient呈現正相關，而高帶電量的液滴，其dipole coefficient隨電場頻率有明顯的極值出現。液滴黏度則和dipole coefficient負相關，且黏度低和高者，dipole coefficient差距可能達2倍或以上。介電常數決定了高頻下的dipole coefficient，且有上限及下限值存在。最後，與實驗數據比對十分吻合，代表本文可有效且合理地預測實驗結果。

關鍵字

介電質；介電泳；交流電場；電動力學；液滴；有效偶極矩；電雙層極化效應

並列摘要

Dielectrophoresis (DEP), the migration of a dielectric in a non-uniform electric field, has grabbed a great deal of interest in micro/nano-technologies such as microfluidic devices, biomaterial and lab-on-a-chip. However, relevant theoretical researches are still limited. In addition, there exist various kinds of particles other than traditional rigid one, including liquid droplets and biological cells, which cannot be modeled as rigid particles. In present study, the effective polarization, characterized by the dipole coefficient, of a charged liquid droplet in an electrolyte solution and subjected to an alternating electric field, is studied theoretically with the electrokinetic model. Dipole coefficient is calculated as a function of the double-layer thickness, the droplet’s surface charge, viscosity, permittivity and the electric-field frequency. The electrophoretic motion seriously influences the electric double layer and thus polarizability. First, Positive correlation between dipole coefficient and the particle’s surface charge is found. Second, the dipole coefficient of the highly-charged droplet reaches local maximum when plotted versus frequency. Oppositely, the dipole coefficient and the droplet’s viscosity are in negative correlation. Dipole coefficient of the low-viscosity droplet is two or more times greater than that of the high-viscosity one. The permittivity alters the dipole coefficient in a limited range at high frequencies. In the last part, our theoretical predictions are compared with experimental data. The good agreement between them leads to a conclusion that our model is able to adequately predict the experimental results.

並列關鍵字

dielectric ； dielectrophoresis ； AC electric field ； electrokinetics ； liquid droplet ； effective dipole moment ； double layer polarization

參考文獻

[1] A.R. Von Hippel, Dielectric materials and applications. Artech House, Boston, 1995.

[2] G. Arlt, D. Hennings, et al., Dielectric properties of fine‐grained barium titanate ceramics. Journal of Applied Physics 58, 1619 (1985).

[3] H.A. Pohl, The Motion and Precipitation of Suspensoids in Divergent Electric Fields. Journal of Applied Physics 22, 869 (1951).

[4] C. Zhang, K. Khoshmanesh, et al., Dielectrophoresis for manipulation of micro/nano particles in microfluidic systems. Analytical and bioanalytical chemistry 396, 401 (2010).

[5] C. Qian, H. Huang, et al., Dielectrophoresis for bioparticle manipulation. International Journal of Molecular Sciences 15, 18281 (2014).

國際替代計量

液滴於電解質溶液中之介電泳現象

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