电场强度对液滴振荡及起跳运动的影响

Study on Droplet Vibration and Bouncing Under Vertical Electric Field

本文通过可视化实验观察了液滴在垂直电场下的振荡变形、起跳及运动行为.实验发现,随着电压的升高,具有超疏水性质的下极板表面上的液滴起跳行为会出现三种不同的模式,第一种模式,液滴起跳前会发生持续振荡的过程,振荡过程中,液滴会发生周期性的拉伸与收缩的过程,直到液滴成功离开壁面,并加速运动到上极板壁面;第二种模式,液滴起跳前仍出现振荡的现象,但是当液滴离开壁面并运动一定距离后,会回落至下极板,随后液滴由于撞击作用发生压缩碰撞,最后起跳并加速运动至上极板;第三种模式,液滴会直接拉伸并迅速脱离表面,起跳至上极板,起跳前不会发生上下振荡的现象,也不会有回落的现象.在三种模式中,库仑力、液滴表面张力、液滴自身重力和壁面黏附力间的相互影响和耦合作用是出现三种模式的重要原因.最后,利用MATLAB分别对三种情况进行图像处理,分析了表面能在液滴起跳过程中的变化规律,发现变形过程中液滴表面能的释放程度是影响液滴起跳后有无回落现象的主导因素。

In this paper, visualization experiments were carried out on the jumping and vibration characteristics of liquid droplets under vertical electric field. Experiments found that three dynamics modes would occur before drops jumping on the superhydrophobic surface as the increase of applied voltage: First, the water droplet first periodically develops elongating and contraction in the vertical direction until it jumps off from the superhydrophobic electrode and stick on the upper one. Second,the droplet is first elongated to a certain height, and then it departs from substrates but it can fall and hit the bottom electrode, and the droplet continues to vibration until it can bounce from the bottom surface. Third, the droplet is elongated quickly and removed from electrode without any oscillation or retreating phenomenon. The three modes can be considered as the combined effect of liquid surface tension, gravity and adhesion force between liquid and solid. Finally, we analyzed the change in droplets surface area for three modes through Matlab software. We found that the surface energy releasing plays an important role in the retreating phenomenon for drops jumping.