Suzuki Tamako, Sawada Hideyuki
Department of Pure and Applied Physics, Graduated School of Advanced Science and Engineering, Waseda University 3-4-1 Okubo, Shinjuku-Ku Tokyo 169-8555 Japan
Faculty of Science and Engineering, Waseda University 3-4-1 Okubo, Shinjuku-Ku Tokyo 169-8555 Japan.
RSC Adv. 2025 May 7;15(19):14787-14796. doi: 10.1039/d4ra09004g. eCollection 2025 May 6.
This study aims to analyze the convection flow generated three-dimensionally around and inside a 1-pentanol droplet dropped into a 1-pentanol aqueous solution. The difference in concentration between the droplet and the aqueous solution causes an interfacial tension gradient, and then the droplet starts moving in the aqueous solution. The droplet shape is closely related to its self-propulsion behavior because the interfacial tension gradient changes with the droplet shape. In this study, we fix the droplet shape using an exoskeleton to control the self-propulsion direction. The exoskeleton is fabricated by using OHP film with a circular-shape having a hole in the center, and a droplet is dropped into the hole to fix the droplet shape. We prepared two different exoskeletons having symmetrical elliptical holes and asymmetrical elliptical holes. We also prepare two different concentrations of aqueous solutions. By using two different concentrations of aqueous solution and two types of exoskeletons, we analyze the behavior of the droplet dropped into the exoskeleton hole, in relation with the convection around and inside the droplet. The results indicate that the self-propulsion direction of the droplet is determined by the shape of the droplet, which is fixed by the exoskeleton. Particularly in the case of the asymmetrical exoskeleton, the self-propulsion direction is fixed in one direction. The self-propulsion velocity of the droplets changed depending on the concentration of the aqueous solution, and we observed the droplet to self-propel several times per 50 seconds when the aqueous solution of smaller concentration was used. Based on these experimental results, we discuss the dominant factors to determine the self-propulsion direction by visualizing the convection around and inside the droplet.
本研究旨在分析将1-戊醇液滴滴入1-戊醇水溶液中时，在液滴周围及内部三维产生的对流。液滴与水溶液之间的浓度差异会导致界面张力梯度，进而使液滴在水溶液中开始移动。液滴形状与其自推进行为密切相关，因为界面张力梯度会随液滴形状而变化。在本研究中，我们使用外骨骼固定液滴形状以控制自推进方向。外骨骼是通过使用中心有孔的圆形OHP膜制成的，将液滴滴入孔中以固定液滴形状。我们制备了两种不同的外骨骼，分别具有对称椭圆孔和不对称椭圆孔。我们还制备了两种不同浓度的水溶液。通过使用两种不同浓度的水溶液和两种类型的外骨骼，我们分析了滴入外骨骼孔中的液滴行为，以及与液滴周围和内部对流的关系。结果表明，液滴的自推进方向由外骨骼固定的液滴形状决定。特别是在不对称外骨骼的情况下，自推进方向固定在一个方向上。液滴的自推进速度随水溶液浓度而变化，当使用较低浓度的水溶液时，我们观察到液滴每50秒自推进几次。基于这些实验结果，我们通过可视化液滴周围和内部的对流来讨论决定自推进方向的主导因素。
