Experimental study on the characteristic motion of bubble propelled hollow Janus microspheres
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摘要: 本文通过Pt-SiO2型（铂-二氧化硅型）中空Janus微球在低浓度2%~4% H2O2溶液中的气泡驱动实验，观察到在每个气泡生长-溃灭周期内，Janus微球的运动呈现3个特征阶段，分别为自扩散泳、气泡生长和气泡溃灭。其中气泡溃灭阶段微球在射流驱动下的推进速度可达每秒几十毫米，比前2个阶段的平均速度大2~3个数量级。实验观察到气泡生长阶段其半径与时间存在Rb~t1/3和Rb~t1/2两种标度率。由于气泡在Janus微球催化剂表面（Pt侧）的生长点偏离对称轴位置，Janus微球的运动轨迹呈圆周形。随H2O2溶液浓度的增加，还可以进一步提高Janus微球的运动速度。此研究不仅定量分析了Janus微球的运动特性，而且为实际应用中提高Janus双面微马达的运动速度和能量利用率提供了参考依据。Abstract: This paper studies the bubble propelled motion of Pt-SiO2 hollow Janus microspheres in H2O2 solutions (concentrations between 2% to 4%). Three typical stages have been observed in every period of the bubble growth-collapse, which are self-diffusiophoresis, bubble growth and bubble collapse. At the bubble collapse stage, the speed propelled by a microjet can reach tens of millimeter per second, and it is about 2 or 3 orders of magnitude higher than the speed in the other two stages. In the experiment, two scaling laws between the bubble radius and the elapsed time during the bubble growth stage are observed: Rb~t1/3 and Rb~t1/2. Because the bubble growing point at the Janus microsphere's Pt side deviates from the axisymmetric point, the trajectory of the Janus microsphere is nearly a circle.With the increase of the H2O2 concentrations, the speed of the Janus microspheres can be enhanced.This study not only quantifies the characteristic motion of Janus microspheres, but also provides valuable information for improving the speed and energy utilization of Janus micromotors in practical application.
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Key words:
- hollow Janus microsphere /
- bubble propelled motion /
- bubble collapse
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图 1 (a) 电子束蒸发制备Janus微球的示意图; (b) 显微图像
Figure 1. (a) Schematic to show the fabrication of Pt-SiO2 type Janus microspheres (JMs). (b) Optical image of a Pt-SiO2 type JM
图 2 单个周期内气泡生长与溃灭的实验图像 (dp=20.0μm，CH2O2= 3%)
Figure 2. Experimental image of bubble's growth and collapse in a single period (dp= 20.0μm and CH2O2 = 3%)
图 4 4个Janus微球的无量纲位移L/dp与时间t的关系
Figure 4. Relationship of normalized displacement L/dp for four JMs and time t
图 5 Janus微球位移L与气泡半径Rb随时间t的变化
Figure 5. JM displacement L and the bubble radius Rb vs. time t
图 8 气泡在Janus微球表面生长点的实验照片与示意图
Figure 8. Experimental image and schematic of bubble growth position on JM surface
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