Liu Hailong, Zheng Nuo, Chen Jiaqi, Yang Ding, Wang Junfeng
School of Energy and Power Engineering, Jiangsu University, Zhenjiang, China, 212013.
Langmuir. 2023 Mar 21;39(11):3979-3993. doi: 10.1021/acs.langmuir.2c03298. Epub 2023 Mar 10.
The control of a droplet bouncing on a substrate is of great importance not only in academic research but also in practical applications. In this work, we focus on a particular type of non-Newtonian fluid known as shear-thinning fluid. The rebound behaviors of shear-thinning fluid droplets impinging on a hydrophobic surface (equilibrium contact angle θ ≈ 108°and contact angle hysteresis Δθ ≈ 20°) have been studied experimentally and numerically. The impact processes of Newtonian fluid droplets with various viscosities and non-Newtonian fluid droplets with dilute xanthan gum solutions were recorded by a high-speed imaging system under a range of Weber numbers () from 12 to 208. A numerical model of the droplet impact on the solid substrate was also constructed using a finite element scheme with the phase field method (PFM). The experimental results show that unlike the Newtonian fluid droplets where either partial rebound or deposition occurs, complete rebound behavior was observed for non-Newtonian fluid droplets under a certain range of . Moreover, the minimum value of required for complete rebound increases with xanthan concentration. The numerical simulations indicate that the shear-thinning property significantly affects the rebound behavior of the droplets. As the amount of xanthan increases, the high shear rate regions shift to the bottom of the droplet and the receding of the contact line accelerates. Once the high shear rate region appears only near the contact line, the droplet tends to fully rebound even on a hydrophobic surface. Through the impact maps of various droplets, we found that the maximum dimensionless height of the droplet increases almost linearly with as ∼ . In addition, a critical value for the distinction between deposition and rebound for droplets on the hydrophobic surface has been theoretically derived. The prediction of the model shows good consistency with the experimental results.
控制液滴在基底上的弹跳不仅在学术研究中，而且在实际应用中都具有重要意义。在这项工作中，我们专注于一种特殊类型的非牛顿流体，即剪切变稀流体。对撞击疏水表面（平衡接触角θ≈108°且接触角滞后Δθ≈20°）的剪切变稀流体液滴的回弹行为进行了实验和数值研究。在一系列韦伯数（）从12到208的情况下，用高速成像系统记录了不同粘度的牛顿流体液滴和含稀黄原胶溶液的非牛顿流体液滴的撞击过程。还使用相场法（PFM）的有限元方案构建了液滴撞击固体基底的数值模型。实验结果表明，与牛顿流体液滴发生部分回弹或沉积不同，在一定范围内的非牛顿流体液滴观察到了完全回弹行为。此外，完全回弹所需的最小值随黄原胶浓度增加。数值模拟表明，剪切变稀特性显著影响液滴的回弹行为。随着黄原胶含量的增加，高剪切速率区域移至液滴底部，接触线后退加速。一旦高剪切速率区域仅出现在接触线附近，液滴即使在疏水表面上也倾向于完全回弹。通过各种液滴的撞击图，我们发现当～时，液滴的最大无量纲高度几乎随线性增加。此外，从理论上推导了疏水表面上液滴沉积和回弹区分的临界值。模型预测与实验结果显示出良好的一致性。
