自推进液滴的溶质诱导抖动运动
Solute Induced Jittery Motion of Self-Propelled Droplets
摘要：
研究了溶质在自推进液滴中的作用。研究了4-戊基-4-联苯腈（5CB）在十四烷基三甲基溴化铵（TTAB）水溶液中的自推进微滴体系。结果表明，甘油的加入导致活性5CB液滴表现出从平滑到抖动运动的过渡。该运动被发现是独立的液滴的大小和的5CB的微扰状态。用聚丙烯酰胺（PAAm）、聚乙烯吡咯烷酮（PVP）和聚乙烯醇（PVA）作为溶质的类似实验证实，这种转变不能仅仅基于系统的粘度或Peclet数来解释。我们建议，溶质和液滴界面之间的物理化学相互作用的具体性质是在这个过渡的根源。实验表明，溶质的存在改变了界面处表面活性剂的流入和再分布的时间尺度。甘油和PVP显著提高了5CB液滴的溶解速率，导致吸附的TTAB分子在界面上更快地重新分布，导致液滴暂时停止，然后在独立的方向上重新开始。另一方面，在PAAm和PVA存在下的低增溶速率导致平滑的轨迹。我们的假设是支持液滴尺寸和界面速度测量的存在和不存在溶质的时间演变。总的来说，我们的研究结果提供了基本的见解复杂的相互作用出现由于溶质的存在。
英文摘要：
The intriguing role of the presence of solutes in the activity of a self-propelling droplet is investigated. A system of self-propelling micron sized 4-pentyl-4-biphenylcarbonitrile (5CB) droplets in an aqueous solution of tetradecyltrimethylammonium bromide (TTAB) as surfactant is considered. It is shown that addition of glycerol causes the active 5CB droplet to exhibit a transition from smooth to jittery motion. The motion is found to be independent of the droplet size and the nematic state of 5CB. Analogous experiments with Polyacrylamide (PAAm), Polyvinylpyrrolidone (PVP) and Polyvinyl Alcohol (PVA), as solutes confirm that such a transition cannot merely be explained solely based on the viscosity or Peclet number of the system. We propose that the specific nature of physicochemical interactions between the solute and the droplet interface is at the root of this transition. The experiments show that the time-scales associated with the influx and redistribution of surfactants at the interface are altered in the presence of solutes. Glycerol and PVP significantly enhance the rate of solubilization of the 5CB droplets resulting in a quicker re-distribution of the adsorbed TTAB molecules on the interface, causing the droplet to momentarily stop and then restart in an independent direction. On the other hand, low solubilization rates in the presence of PAAm and PVA lead to smooth trajectories. Our hypothesis is supported by the time evolution of droplet size and interfacial velocity measurements in the presence and absence of solute. Overall, our results provide fundamental insights into the complex interactions emerging due to the presence of solutes.
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