非對稱粒子在自發熱梯度下的電旋轉與交互作用

Electrorotation of Janus Particles and Particle-Particle Interaction under Self-Generated Thermal Gradient

楊承翔(Cheng-Xiang Yang)

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(2017年)

https://doi.org/10.6342/NTU201702099

摘要

近幾年科學家研究中，以施加電場來控制膠體粒子運動，此技術可應用用於藥物輸送、自組裝及細胞分離，而粒子於電場中的運動主要由其極化能力決定，因此以電旋轉方式來量測粒子旋轉角速度與頻率關係，藉此了解粒子的極化特性，另外改變溶液性質及粒徑大小變因等，能導致粒子電旋轉特徵頻率改變，而在過去還未以溫度作為變因來探討，因而我們在旋轉電場中以動態方式施加雷射於粒子上，來觀察粒子運動變化。而粒子於具有溫度梯度系統中會有熱泳現象，在Janus粒子研究中，其在擴束雷射照射下，金屬端吸收雷射產生溫度梯度而產生自熱泳，然而科學家對於粒子在電熱耦合下的泳動，還對此機制未有完整了解，因此本實驗結合兩種機制，對Janus粒子同時施加旋轉電場及熱場作為實驗對象，觀察電熱耦合下Janus粒子運動。
我們實驗中，在低頻時Janus粒子產生偏心自發熱推進旋轉運動，這種新的主動粒子運動型態的推進速度、旋轉半徑及旋轉方向能藉由電壓、雷射功率及頻率控制，Janus粒子推進速度會與電場強度及雷射功率呈正相關。而在高頻率時Janus粒子周圍液體產生順電場方向的電熱流動，而電熱流動會對Janus粒子產生扭矩造成同方向旋轉，另外系統下Janus粒子能匯聚並捕獲負介電泳粒子並排斥正介電泳粒子。這些電熱耦合下產生的特殊現象，未來能應用在微晶片上溶液混合及細胞收集控制。

關鍵字

Janus粒子 ； 極化特性 ； 電旋轉 ； 熱泳 ； 電熱耦合

並列摘要

The responses of colloidal particles under electric fields have been intensively studied. This technique can be applied to drug delivery, self-assembly and cell separation. The movement of particles under the electric field is mainly determined by polarizability which can be obtained by using the electrorotation method. The characteristic frequency of electrorotation can be changed by the solution properties or the size of particles. However, these reports did not consider the influence of temperature. Therefore, we apply a defocused laser on the Janus particles under the rotating electric field. The metal-coated side of Janus particles absorb the laser and create local temperature gradient which propulses the particles. However, the scientists have not fully understood the motions of particles under the electro-thermal coupling field, so we measure the motions of laser-heated Janus particles under a rotating electric field.
In this study, a new active circular motion of Janus particles is observed at low frequency. The propulsive velocity of Janus particles, rotation radius and rotation direction of this circular motion can be controlled by voltage, laser power and frequency. At the high frequency, electrothermal flows occur around the Janus particles. Besides, the Janus particles in the system can be used to concentrate the negative dielectrophoresis particles and exclude the positive dielectrophoresis particles. These special phenomena can be applied to solution mixing and cell collection on microchips.

並列關鍵字

Janus particle ； Polarizability ； Electrorotation ； Thermophoresis ； Electrothermal

參考文獻

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