Article
Multidisciplinary Sciences
Yuhang Dai, Minfei Li, Bingqiang Ji, Xiong Wang, Siyan Yang, Peng Yu, Steven Wang, Chonglei Hao, Zuankai Wang
Summary: Liquid metal has been widely used in applications such as flexible electronics and soft robots due to its low melting temperature, good flexibility, and high electrical and thermal conductivity. Researchers have discovered that liquid metal droplets can completely rebound from surfaces covered with a water film of sufficient thickness, and the rebound coefficient increases with the thickness of the water film. This finding advances the understanding of droplet dynamics in complex fluids and provides insights for fluid control.
NATURE COMMUNICATIONS
(2023)
Article
Mechanics
Shi-Zheng Wang, Xianfu Huang, Longquan Chen, Ying-Song Yu
Summary: Water droplets impinging on micro-grooved polydimethylsiloxane surfaces were investigated, and various phenomena including no bouncing, complete rebound, bouncing occurring with droplet breakup, partial rebound, and sticky state were observed depending on the impact velocity and surface roughness. The lower limit of impact velocity for bouncing droplets was determined by balancing the droplet's kinetic energy with the energy barrier caused by contact angle hysteresis. The upper limit of impact velocity was predicted by recording droplet impact at an ultrahigh speed and correlating the transition from complete rebound to bouncing with the wetting state transition. A theoretical model was developed to predict the upper limit of impact velocity by considering the liquid penetration into the micro-grooves. Additionally, the contact time of bouncing droplets decreased with decreasing Weber number, while surface roughness had a minor influence on the contact time in the experiments.
Article
Mechanics
Gaurav Upadhyay, Vedant Kumar, Rajneesh Bhardwaj
Summary: Studying the impact dynamics of a water droplet on a superhydrophobic flexible substrate reveals energy conversion and rebound phenomena during impact. By altering the characteristic timescales of the droplet and cantilever beams, the overall system dynamics are influenced.
Article
Thermodynamics
Chuchen Yue, Qingwen Dai, Wei Huang, Xiaolei Wang
Summary: This study reports on droplets bouncing on curved surfaces with elevated temperatures, confirming the bouncing and depositing phenomena of different lubricant droplets. The influence of initial diameter, tangential velocity, and surface roughness on the impact dynamics of silicone oil droplets on wetted curved surfaces is investigated, with emphasis on the temperature dependence of the bouncing phenomenon. Bouncing and depositing thresholds under various conditions are summarized, with surface roughness having the most significant negative effect on the bounceable velocity range, followed by initial diameter and tangential velocity. A theoretical model and force analysis are established to explain the bouncing mechanism, while modified Bond numbers and Ohnesorge numbers are introduced to predict the bouncing thresholds. This work provides sufficient experimental and theoretical insights into manipulating droplets bouncing on wetted and curved surfaces with elevated temperatures.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2023)
Article
Chemistry, Multidisciplinary
Calvin Thenarianto, Xue Qi Koh, Marcus Lin, Ville Jokinen, Dan Daniel
Summary: A water droplet can rebound multiple times on superhydrophobic surfaces, and the energy loss during such rebounds depends on the ratio of rebound speed to initial impact speed. We conducted experiments on different superhydrophobic surfaces with droplets of various sizes and proposed scaling laws to explain the nonmonotonic relationship between the energy loss and impact speed. At low impact speeds, the energy loss is influenced by contact-line pinning and the surface wetting properties, while at high impact speeds, it is dominated by inertial-capillary effects.
Article
Thermodynamics
Shusheng Zhang, Li-Zhi Zhang
Summary: The article introduces the effectiveness of superhydrophobic surface modifications in minimizing heat exchange between impacting droplets and solid surfaces. By developing a multiple distribution function phase-field lattice Boltzmann model, the dynamic behaviors and heat transfer during droplet impact are studied, with a detailed discussion on the effects of textured surface structural parameters. The numerical results reveal four possible bouncing modes of impacting droplets, depending on the surface energy stored in microstructure cavities. Additionally, the synergistic effects of contact time and contact area impact the heat transfer performance.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2024)
Review
Engineering, Environmental
Yue Fan, Yao Tan, Yingying Dou, Shilin Huang, Xuelin Tian
Summary: This review systematically summarizes the research progress in reducing the contact time of impacting droplets on superhydrophobic surfaces, including droplet impact theory, classification of strategies to reduce contact time, and representative applications.
CHEMICAL ENGINEERING JOURNAL
(2023)
Article
Chemistry, Physical
Jiayu Du, Yanzhi Li, Xinxin Wu, Qi Min
Summary: In this study, millimeter superhydrophobic stepped surfaces were designed to achieve highly steerable directional bouncing and reduction of contact time for impacting droplets. The experimental results demonstrated that the stepped surfaces outperformed microtextured surfaces in terms of performance.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2023)
Article
Chemistry, Multidisciplinary
Yang Liu, Yizhou Liu, Min Chen
Summary: In this work, we investigated the maximum spreading of bouncing droplets in the capillary regime at ultralow Weber numbers with a fixed static contact angle. We found that existing spreading laws are not applicable in the ultralow Weber number region, due to gravity exclusion and change in deformation shape. We proposed a theoretical scaling law based on energy conservation, modeling the deformed droplet as an ellipsoid with gravity effects. The proposed scaling law reveals the competition between gravity and inertia at ultralow Weber numbers and distinguishes their dominant regimes. We also discovered the prominent role of viscosity in the previously assumed inviscid regime by integrating higher Weber number regions. Furthermore, we devised a phase diagram to clarify different impact regimes based on energy analysis.
Article
Mechanics
Ryan McGuan, R. Candler, H. P. Kavehpour
Summary: This paper investigates the phenomenon of partial coalescence in a viscous quiescent medium using a liquid metal alloy. The study observes the bouncing of coalescing droplets on the interface and develops models to predict droplet velocity, position, and maximum bounce height.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Computer Science, Interdisciplinary Applications
Jiayi Zhao, Shuo Chen, Kaixuan Zhang, Damin Cao, Yang Liu
Summary: This study investigates the bouncing dynamics of droplets on a surface with a macro-textured ridge by numerical simulation and theoretical analysis. The bouncing dynamics can be classified into jug-like behavior with asymmetric retracting velocity and wing-like behavior with rotation of the sub-droplets. The angular velocity of droplets during rebounding plays a crucial role in determining the contact time.
COMPUTERS & FLUIDS
(2022)
Article
Chemistry, Physical
Konghua Yang, Qi Liu, Zhaohua Lin, Yunhong Liang, Chunbao Liu
Summary: This study investigates the directional transportation of droplets using a mixed-wettability surface inspired by kingfishers' feathers. Experimental testing and numerical modelling show that the anisotropic surface can convert vertical impacting to horizontal droplets transport. The intensity and patterns of the thrown droplets are controlled by the wettability and surface offset location. The optimized surfaces can achieve a maximum horizontal transport distance of up to 6.2D0, with a first desorption time of only 7.8 ms. These findings have important implications for engineering designs in anti-icing, lubrication, and spray cooling applications.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2022)
Article
Chemistry, Physical
Surjyasish Mitra, Quoc Vo, Tuan Tran
Summary: The research shows that liquid droplets impact more air on soft surfaces and observes the phenomenon of dimple inversion causing rupture of the air film, affecting the bouncing behavior of the droplets.
Article
Mathematics, Applied
Yudai Okishio, Hiroaki Ito, Hiroyuki Kitahata
Summary: In this study, a system consisting of a ball bouncing off a sawtooth-shaped table vibrating vertically is examined. The mean horizontal velocity is plotted against the asymmetry of the table shape, and it is found that the ball is transported in the direction of the gentler slopes in the high-bounce parameter region. To explain this asymmetric transport, a simplified model based on high bounce and probabilistic collision to the left or right slopes is derived. The simplified model exhibits a qualitatively similar horizontal transport to that observed in the original model.
PHYSICA D-NONLINEAR PHENOMENA
(2023)
Article
Engineering, Environmental
Kongbo Wang, Ali Naderi Bakhtiyari, Yongling Wu, Mingming Liu, Hongyu Zheng
Summary: This paper studied superhydrophobic magnetically responsive micro-plate arrays with reverse switching wettability for capturing, releasing, and bouncing droplets over a large distance. A novel method of laser texturing was used to create a superhydrophobic pattern on one side of the micro-plates, and the directional bouncing of droplets was achieved through the instantaneous response to a magnetic field. This research provides a new approach for flexible droplet manipulation and reagent transfer applications.
CHEMICAL ENGINEERING JOURNAL
(2023)