Miura Shingo, Banno Taisuke, Tonooka Taishi, Osaki Toshihisa, Takeuchi Shoji, Toyota Taro
Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo , 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan.
Langmuir. 2014 Jul 15;30(27):7977-85. doi: 10.1021/la5018032. Epub 2014 Jun 27.
Self-propelled motion of micrometer-sized substances has drawn much attention as an autonomous transportation system. One candidate vehicle is a chemically driven micrometer-sized oil droplet. However, to the best of our knowledge, there has been no report of a chemical reaction system controlling the three-dimensional motion of oil droplets underwater. In this study, we developed a molecular system that controlled the self-propelled motion of 4-heptyloxybenzaldehyde oil droplets by using novel gemini cationic surfactants containing carbonate linkages (2G12C). We found that, in emulsions containing sodium hydroxide, the motion time of the self-propelled oil droplets was longer in the presence of 2G12C than in the presence of gemini cationic surfactants without carbonate linkages. Moreover, in 2G12C solution, oil droplets at rest underwent unidirectional, self-propelled motion in a gradient field toward a higher concentration of sodium hydroxide. Even though they stopped within several seconds, they restarted in the same direction. 2G12C was gradually hydrolyzed under basic conditions to produce a pair of the corresponding monomeric surfactants, which exhibit different interfacial properties from 2G12C. The prolonged and restart motion of the oil droplets were explained by the increase in the heterogeneity of the interfacial tension of the oil droplets.
微米级物质的自驱动运动作为一种自主运输系统已备受关注。一种候选载体是化学驱动的微米级油滴。然而，据我们所知，尚未有关于控制水下油滴三维运动的化学反应系统的报道。在本研究中，我们开发了一种分子系统，通过使用含碳酸酯键的新型双子阳离子表面活性剂（2G12C）来控制4-庚氧基苯甲醛油滴的自驱动运动。我们发现，在含有氢氧化钠的乳液中，存在2G12C时自驱动油滴的运动时间比存在不含碳酸酯键的双子阳离子表面活性剂时更长。此外，在2G12C溶液中，静止的油滴在梯度场中朝着更高浓度的氢氧化钠进行单向自驱动运动。即使它们在几秒钟内停止，也会在同一方向重新开始运动。2G12C在碱性条件下逐渐水解，生成一对相应的单体表面活性剂，它们表现出与2G12C不同的界面性质。油滴运动时间的延长和重新开始运动可以通过油滴界面张力不均匀性的增加来解释。
