多層的非對稱粒子在交流電場下的電旋轉研究

Electrorotation of Multi-Layer Janus Particles under AC Electric Field

吳龍魁(Lung-Kuei Wu)

指導教授 ： 江宏仁

國立臺灣大學/工學院/應用力學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202000491

摘要

在近十幾年來，因Janus粒子特殊結構性的關係，使其在不同領域上受到諸多學者的注意，漸漸研究出許多不同的應用，其為利用電場來控制Janus粒子的運動以達到藥物輸送、自組裝或細胞分離的目的，而要達到Janus粒子控制的目的前，首先須先瞭解Janus粒子受到電場作用後，其極化機制對於粒子運動的影響，而從文獻上可知目前探討膠體粒子的極化特性的方法，主要以電旋轉或介電泳的技術來量測不同頻率下的膠體粒子（角）速度的差異，並透過改變粒子大小或是溶液導電度的變因，探討其因極化能力的改變而導致特徵頻率改變之原因。由於最初的膠體粒子極化機制並沒有考慮到溶液中固液介面形成的電雙層對極化的影響，因此在後來便有將電雙層因素考慮進邊界條件的膠體粒子極化機制的數學理論推導，但整體的極化過程目前還不是太明確，再加上後來的特殊結構的Janus粒子的極化特性所發現的不同於膠體粒子的極化能力且無法使用膠體粒子的極化理論來解釋，因此使得Janus粒子的極化特性變得更為複雜有趣。
在我們的論文中，我們會先利用模擬的方式來說明膠體粒子及Janus粒子在電旋轉下的極化特性且在不同頻率下對角速度影響及Janus粒子的特徵頻率放大且低頻再次反轉之現象，瞭解兩種粒子的極化機制後，我們將會設計多層的表面結構在Janus粒子的金屬側上，透過實驗的方式以電旋轉技術量測其頻譜，而我們發現了多層結構的Janus粒子其特徵頻率會再次放大且轉速會有下降之現象，為了瞭解其多層結構所影響的粒子極化能力，我們會再使用模擬的方法來輔助瞭解多層結構的Janus粒子其極化機制的改變原因，而從模擬結果上可以知道其極化能力的改變都與電雙層形成的快慢及完整性有關，即電雙層所產生的電偶極矩與粒子本身受到電場作用而感應出的電偶極矩彼此耦合後與電場之間的關係，因此透過本次論文的研究，我們提出了一個模擬的電雙層模型來清楚的解釋膠體粒子及Janus粒子在受到電場作用後的極化機制，接著使用實驗與模擬的方法探討及解釋表面多層的結構如何有效的改變Janus粒子的極化特性，隨著全盤的了解Janus粒子的極化機制及控制極化能力後，或許可以達到設計粒子極化能力之目的，在未來操控粒子的應用或是提供給感測器應用在針對表面結構探測的奈米機器人設計上之資訊。

關鍵字

非對稱粒子 ； 多層結構 ； 電動力學 ； 電旋轉 ； 介電泳 ； COMSOL

並列摘要

Janus particle has attracted the attention in the different academic fields due to the special structure in last decades. Scientists reported that this special particle can be applied to the drug delivery, self-assembly and cell separation under electric field.
In order to achieve the purpose of controlling Janus particle, we must understand its polarization mechanism. The widely used methods of measuring the polarization characteristics of particles are Electrorotation(EROT) and Dielectrophoresis(DEP), which analyze the angular velocity of particles in many literatures. But the original polarization mechanism of colloidal particles did not take into account the effect of the electric double layer formed on the solid-liquid interface in solution. Although there are some mathematical theories take the electric double layer factor into the consideration, the entire polarization process is still not clear. Janus particles with specific structures are more complicated, so the polarization of colloidal particles from previous literatures can not well explain its polarization characteristics.
In this study, we investigate the physical mechanism occurred in the process of electrorotation of colloidal particles and Janus particles by simulation. After analyzing the polarization mechanism of two kinds of particles, we design a multilayer structure which composed of silica and platinum on the metal coated side of the Janus particle and measure its frequency spectrum by electrorotation. We find that the characteristic frequency of Janus particles with multilayer structure will increase and the angular velocity will decrease. In order to verify our discovery, we investigate the polarization mechanism of the multilayer structure of Janus particles by numerical simulation method. We find that the polarization mechanism is related to the electric double layer by simulation results. Therefore, we report an electric double layer model through numerical method to clearly explain the polarization mechanism of colloidal particles and Janus particles. We use experimental method and numerical simulation to explore how the multilayer structure on the surface effectively changes the polarization characteristics of Janus particles. After studying the polarization mechanism of Janus particles, we may be possible to design the behavior of particle polarization.

並列關鍵字

Janus particle ； multi-layer ； electrokinetics ； electrorotation ； dielectrophoresis ； COMSOL

參考文獻

[1] E. Poggi and J.-F. Gohy, "Janus particles: from synthesis to application," Colloid and Polymer Science, vol. 295, no. 11, pp. 2083-2108, 2017.

[2] Q. Zhang, S. Savagatrup, P. Kaplonek, P. H. Seeberger, and T. M. Swager, "Janus emulsions for the detection of bacteria," ACS central science, vol. 3, no. 4, pp. 309-313, 2017.

[3] M. Yoshida et al., "Structurally controlled bio‐hybrid materials based on unidirectional association of anisotropic microparticles with human endothelial cells," Advanced materials, vol. 21, no. 48, pp. 4920-4925, 2009.

[4] Y.-L. Chen and H.-R. Jiang, "Particle concentrating and sorting under a rotating electric field by direct optical-liquid heating in a microfluidics chip," Biomicrofluidics, vol. 11, no. 3, p. 034102, 2017.

[5] T. B. Jones and T. B. Jones, Electromechanics of particles. Cambridge University Press, 2005.