Lee Jongju, Murad Sohail, Nikolov Alex
Department of Chemical and Biological Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, United States.
Langmuir. 2024 Dec 31;40(52):27356-27363. doi: 10.1021/acs.langmuir.4c03569. Epub 2024 Dec 16.
Despite its important technological applications, surfactant-enhanced (spontaneous) spreading on a solid surface and how to optimize it on surfaces with different wettabilities are not well understood. Spontaneous spreading involves a surface tension gradient (Marangoni stresses), which enhances spreading over a large area. Experimental observations reveal that the spreading rate and surfactant concentration have an optimum substrate wettability of 60 ± 5° (Hill, R. M. 1998, 3, 247).This paper discusses why the optimum for surfactant-enhanced spreading requires an initial macroscopic three-phase contact angle of 60 ± 5°. An equation based on experimental evidence allows for the calculation of the surface tension gradient over time using data on the spreading rate, spreading macroscopic contact angle, and droplet spreading radius. This novel approach for estimating the surface tension gradient and explaining the optimum substrate wettability underscores the role of the surface tension gradient, viscosity, and substrate wettability in surfactant-enhanced spreading on solids. The roles of the spreading three-phase contact angle and surface tension gradient in surfactant-enhanced spreading were analyzed, demonstrating that the surface tension gradient contributes more significantly to the spreading rate than the contact angle. Fingering instability formation, an instability at the droplet spreading edge caused by the Marangoni stresses, also serves as evidence of the role that the surface tension gradient plays in surfactant-enhanced spreading. Furthermore, applications of surfactant-enhanced spreading were demonstrated, suggesting potential uses in oil spill removal, leaf pesticide delivery, and oil spill remediation. The goal of the proposed study is to use experimental evidence to develop a model for calculating the optimum spreading rate during the first several seconds of surfactant-enhanced spreading on a solid substrate.
尽管表面活性剂增强（自发）在固体表面的铺展具有重要的技术应用，但对于其在不同润湿性表面上的铺展情况以及如何进行优化，目前仍未得到充分理解。自发铺展涉及表面张力梯度（马兰戈尼应力），这会增强在大面积上的铺展。实验观察表明，铺展速率和表面活性剂浓度在底物润湿性为60±5°时达到最佳（希尔，R.M. 1998年，第3卷，第247页）。本文讨论了为何表面活性剂增强铺展的最佳条件需要初始宏观三相接触角为60±5°。基于实验证据的一个方程，能够利用铺展速率、铺展宏观接触角和液滴铺展半径的数据来计算随时间变化的表面张力梯度。这种估算表面张力梯度并解释最佳底物润湿性的新方法，强调了表面张力梯度、粘度和底物润湿性在表面活性剂增强在固体上的铺展中的作用。分析了铺展三相接触角和表面张力梯度在表面活性剂增强铺展中的作用，表明表面张力梯度对铺展速率的贡献比接触角更为显著。指进不稳定性的形成，即由马兰戈尼应力在液滴铺展边缘引起的一种不稳定性，也证明了表面张力梯度在表面活性剂增强铺展中所起的作用。此外，还展示了表面活性剂增强铺展的应用，表明其在溢油清除、叶片农药输送和溢油修复方面具有潜在用途。本研究的目标是利用实验证据建立一个模型，用于计算表面活性剂在固体底物上增强铺展最初几秒内的最佳铺展速率。
