強電場における誘電性粒子層の帯電および粒子の浮揚

Abstract

電場を利用すると機械的外力を用いることなく帯電粒子に自発的な運動を行わせることができるので, 粒子操作において静電技術が注目されている. 本研究では, 下部に平板電極, 上部に網状電極を用い, 下部電極に誘電性粒子(粒子径100 µmのガラスビーズ)を堆積させて+5 kVの定電圧を印加し, 上部電極を接地して上向きの電場を与えた. 粒子層には下部電極と同じ極性の電荷が誘導帯電によって付与され, 上層の粒子はクーロン力によって浮揚した. 粒子の挙動および浮揚過程を高速度カメラで観察した結果, 一次粒子だけでなく凝集粒子も浮揚することがわかった. 誘電性粒子は静電場で分極し, 静電相互作用によって鎖状凝集粒子を形成した. 粒子の比電荷が小さく, 十分なクーロン力が得られない場合, 粒子は浮揚しないが, 凝集粒子を構成する一次粒子のクーロン力の総和が粒子間付着力および重力を超えると凝集粒子は浮揚した. 電場解析および浮揚した粒子の運動解析によって粒子帯電量を求めた結果, 構成粒子数の増加とともに浮揚凝集粒子の比電荷は小さくなるが, 粒子間付着力は増加することがわかった.

Applying an external electric field enables electrostatically charged particles to move without any external mechanical forces. As a result, electrostatic-based techniques have attracted considerable attention in the field of particle handling. In this experiment, a plate electrode and a mesh electrode were used for lower and upper electrodes, respectively. Dielectric particles (glass beads with particle diameters of 100 µm) were piled on the lower electrode. A voltage of +5 kV was applied to the lower electrode, and the upper electrode was grounded, producing an electric field directed upwards. Owing to induction charging, the electric charge polarity of the particle layer is identical to that of the lower electrode, leading to particles in the upper layer being levitated by the Coulomb forces. The observation of both the particle behavior and the levitation process using a high-speed microscope camera showed that agglomerates as well as individual particles were levitated. The dielectric particles were polarized in the electric field, the electrostatic interaction between which leads to the formation of chain agglomerates. When the specific charge of the particles was small, the resulting Coulomb force was small, and the agglomerate did not levitate. However, when the magnitude of the total Coulomb force of the primary particles consisting the agglomerate exceeded the interparticle and gravitational forces, the agglomerate levitated. Estimating particle charge based on both electric field analysis and particle trajectory analysis showed that the specific charge of the agglomerate decreases and the interparticle force increases with an increase in the number of primary particles in the agglomerate.