Bifurcation of chemically driven self-propelled droplets on a surfactant-adsorbed surface based on spreading coefficients
Bifurcation of chemically driven self-propelled droplets on a surfactant-adsorbed surface based on spreading coefficients
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DOI：
10.1016/j.colsurfa.2021.126563
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发表时间：
2021-04-15
影响因子：
5.2
通讯作者：
Nabika, Hideki
中科院分区：
文献类型：
--
作者：
Ban, Takahiko;Matsumoto, Kohei;Nabika, Hideki
反应流体在固体表面上的自推进运动的分叉对于细胞的趋触性、细胞粘附和活性物质的能量转换具有根本意义。由于化学反应引起的固体表面润湿性的变化与分岔显着相关，其中热力学因素主要考虑基底与液滴的相互作用能，而动力学因素则决定润湿性梯度形成的时间常数。然而，尚未进行定量实验来阐明分岔，考虑非平衡条件下润湿性随时间的变化，以确定热力学和动力学因素对液滴运动的贡献。在这项研究中，我们通过调节周围流体的 pH 值来系统地改变表面活性剂吸附的固体表面的润湿性，并定量研究了阻止自驱动液滴运动的分叉与决定分离压力的扩散系数之间的关系。与尺寸相关的液滴速度与考虑相关化学反应动力学因素的模型的指示一致。此外，当热力学确定的扩散系数的色散分量的符号发生变化时，对应于分离压力方向的变化，就会发生分叉。通过考虑相关化学和物理反应的热力学和动力学因素，我们对随时间变化的扩散系数的分析有可能有助于阐明润湿性梯度变化引起的各种分叉现象。
The bifurcation of the self-propelled motion of a reactive fluid on a solid surface is of fundamental interest in the haptotaxis of cells, cellular adhesion, and the energy conversion of active matter. Changes in the wettability of a solid surface due to chemical reactions are significantly related to bifurcation, with the thermodynamic factors primarily accounting for the substrate?droplet interaction energy, and the kinetic factors determining the time constant of the formation of the wettability gradient. However, no quantitative experiments have been performed to elucidate bifurcation with consideration of the time-dependent change in the wettability under nonequilibrium conditions with the purpose of determining the contributions of the thermodynamic and kinetic factors to droplet motion. In this study, we systematically varied the wettability of a surfactant-adsorbed solid surface by adjusting the pH of the surrounding fluid and quantitatively investigated the relationship between bifurcation, which arrests self-propelled droplet motion, and the spreading coefficient that determine the disjoining pressure. The size-dependent droplet velocity is consistent with the indications of a model that considers the kinetic factors of the relevant chemical reactions. In addition, bifurcation occurred when the sign of the thermodynamically determined dispersive component of the spreading coefficient changed, corresponding to a change in the direction of the disjoining pressure. Our analysis of the time-dependent spreading coefficient has the potential for contributing to the elucidation of various bifurcation phenomena induced by a change in the wettability gradient through consideration of both the thermodynamic and kinetic factors of the relevant chemical and physical reactions.