Kurimura Tomo, Mori Seori, Miki Masako, Yoshikawa Kenichi
Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto 610-0394, Japan.
J Chem Phys. 2016 Jul 21;145(3):034902. doi: 10.1063/1.4958657.
The periodic rotary motion of spherical sub-millimeter-sized plastic objects is generated under a direct-current electric field in an oil phase containing a small amount of anionic or cationic surfactant. Twin-rotary motion is observed between a pair of counter-electrodes; i.e., two vortices are generated simultaneously, where the line between the centers of rotation lies perpendicular to the line between the tips of the electrodes. Interestingly, this twin rotational motion switches to the reverse direction when an anionic surfactant is replaced by a cationic surfactant. We discuss the mechanism of this self-rotary motion in terms of convective motion in the oil phase where nanometer-sized inverted micelles exist. The reversal of the direction of rotation between anionic and cationic surfactants is attributable to the difference in the charge sign of inverted micelles with surfactants. We show that the essential features in the experimental trends can be reproduced through a simple theoretical model, which supports the validity of the above mechanism.
在含有少量阴离子或阳离子表面活性剂的油相中，在直流电场作用下会产生亚毫米级球形塑料物体的周期性旋转运动。在一对对电极之间观察到双旋转运动；也就是说，同时产生两个涡旋，旋转中心之间的连线垂直于电极尖端之间的连线。有趣的是，当阴离子表面活性剂被阳离子表面活性剂取代时，这种双旋转运动会切换到相反方向。我们根据存在纳米级反胶束的油相中的对流运动来讨论这种自旋转运动的机制。阴离子和阳离子表面活性剂之间旋转方向的反转归因于含表面活性剂反胶束电荷符号的差异。我们表明，通过一个简单的理论模型可以重现实验趋势中的基本特征，这支持了上述机制的有效性。
