The effect of drop volume on the apparent contact angle of hierarchical structured superhydrophobic surfaces

2021 ◽  
Vol 611 ◽  
pp. 125849
Author(s):  
Shuai Ren ◽  
Junwu Chen ◽  
Miao Jiang ◽  
Shengwu Wang ◽  
Zhiyu Wan ◽  
...  
Keyword(s):  
Contact Angle ◽  
Apparent Contact Angle ◽  
Superhydrophobic Surfaces ◽  
Drop Volume

Coalescence-induced jumping of nanodroplets on mixed-wettability superhydrophobic surfaces

2020 ◽  
Author(s):  
Fang-Fang Xie ◽  
Dan-Qi Wang ◽  
Yi-Bo Wang ◽  
Yan-Ru Yang ◽  
Xiao-Dong Wang
Keyword(s):  
Contact Angle ◽  
Superhydrophobic Surface ◽  
Apparent Contact Angle ◽  
Superhydrophobic Surfaces ◽  
Dominant Factor ◽  
Heterogeneous Surfaces ◽  
Transfer Enhancement ◽  
Stripe Width ◽  
Mixed Wettability ◽  
Dynamics Simulations

Coalescence-induced droplet jumping on superhydrophobic surfaces has been observed at microscale and even nanoscale. The enhancement in jumping velocity of coalescing droplets is crucial for condensation heat transfer enhancement, anti-icing, self-cleaning, and so forth. However, the research on how to acquire a higher jumping velocity is really very limited. In this paper, we use molecular dynamics simulations to study the coalescence-induced jumping of two equally-sized nanodroplets on chemically heterogeneous surfaces composed of alternating stripes with different hydrophobicity. We show that the jumping velocity is closely related to the stripe width and wettability contrast, and it can even exceed that on an ideal superhydrophobic surface with 180° contact angle when the striped surfaces are properly designed. We also demonstrate that there is always an optimal stripe width yielding the maximum jumping velocity, whereas its value is independent of the wettability contrast. We reveal that the dominant factor to determine the jumping velocity is the apparent contact angle of equilibrated droplets over heterogeneous surfaces for small stripe widths, it changes to the time of liquid bridges impacting surfaces for moderate stripe widths and to the contact area between equilibrated droplets and relatively hydrophobic stripes for large stripe widths. We believe the present simulations can provide useful guidance to design self-jumping superhydrophobic surfaces.

The Energy Transition on Superhydrophobic Surface by Electrowetting Control

2009 ◽  
Vol 79-82 ◽  
pp. 91-94
Author(s):  
Jun Wu ◽  
Jun Xia ◽  
B.P. Wang
Keyword(s):  
Contact Angle ◽  
Silicon Nanowires ◽  
Superhydrophobic Surface ◽  
Saline Solution ◽  
Energy Transition ◽  
Apparent Contact Angle ◽  
Superhydrophobic Surfaces ◽  
External Voltage ◽  
Field Temperature ◽  
Substantial Interest

Transition between Wenzel and Cassie states on superhydrophobic surface has attracted substantial interest from various research communities. The transition between the two states is realized by the methods of changing surface structure in micron scale, or changing the surface tension between a droplet and a solid surface through external electric field, temperature, light, etc. In this paper we design a rough surface on aluminum substrate with the etching processes, on which a large superhydrophobic surface is achieved easily and economically. On this surface, a drop of saline solution water forms a nearly perfect spherical pearl with the apparent contact angle over than 160°. By applying external voltage between the substrate and the solution, we observe a different electrowetting phenomenon from the case on other superhydrophobic surfaces, i.e. on silicon nanowires coated with hydrophobic fluoropolymer C4F8. This difference is discussed and explained by asymmetry of the superhydrophobic surface which increases the hysteresis. A saturated apparent contact angle is also observed as the applied voltage increased to a specific value.

scholarly journals Interfacial Behaviour in Ferroalloys: The Influence of Sulfur in FeMn and SiMn Systems

2021 ◽  
Author(s):  
Sergey Bublik ◽  
Sarina Bao ◽  
Merete Tangstad ◽  
Kristian Etienne Einarsrud
Keyword(s):  
Contact Angle ◽  
Interfacial Tension ◽  
Sessile Drop ◽  
Interfacial Properties ◽  
Apparent Contact Angle ◽  
Holding Time ◽  
Transfer Rates ◽  
Experimental Parameters ◽  
Interfacial Behaviour ◽  
Modelling Approach

AbstractThe present study has investigated the influence of sulfur content in synthetic FeMn and SiMn from 0 to 1.00 wt pct on interfacial properties between these ferroalloys and slags. The effect of experimental parameters such as temperature and holding time was evaluated. Interfacial interaction between ferroalloys and slags was characterized by interfacial tension and apparent contact angle between metal and slag, measured based on the Young–Laplace equation and an inverse modelling approach developed in OpenFOAM. The results show that sulfur has a significant influence on both interfacial tension and apparent contact angle, decreasing both values and promoting the formation of a metal-slag mixture. Despite the fact that sulfur was added only to the ferroalloys, most of sulfur is distributed into slag after reactions with the metal phase. Increasing the maximum experimental temperature in the sessile drop furnace also resulted in a decrease of both interfacial properties, resulting in higher mass transfer rates and intensive reactions between metal and slag. The effect of holding time demonstrated that after reaching equilibrium in FeMn-slag and SiMn-slag systems (both with and without sulfur), interfacial tension and apparent contact angle remain constant.

Relationship between Work of Adhesion and Contact Angle Hysteresis on Superhydrophobic Surfaces

2008 ◽  
Vol 112 (30) ◽  
pp. 11403-11407 ◽  
Author(s):  
Yonghao Xiu ◽  
Lingbo Zhu ◽  
Dennis W. Hess ◽  
C. P. Wong
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Superhydrophobic Surfaces ◽  
Work Of Adhesion

scholarly journals A Simple Method to Create Superhydrophobic Aluminium Surfaces

2012 ◽  
Vol 706-709 ◽  
pp. 2874-2879 ◽  
Author(s):  
R. Jafari ◽  
Masoud Farzaneh
Keyword(s):  
Contact Angle ◽  
Stearic Acid ◽  
Synergistic Effects ◽  
Low Cost ◽  
Contact Angle Hysteresis ◽  
Spray Coating ◽  
Superhydrophobic Surfaces ◽  
Water Contact ◽  
Simple Method ◽  
Static Contact

Superhydrophobic surfaces were prepared using a very simple and low-cost method by spray coating. A high static water contact angle of about 154° was obtained by deposition of stearic acid on an aluminium alloy. However, this coating demonstrated a high contact angle hysteresis (~ 30º). On the other hand, superhydrophobic surfaces with a static contact angle of about 162º and 158º, and a low contact angle hysteresis of about 3º and 5º were respectively obtained by incorporating nanoparticles of SiO2and CaCO3in stearic acid. The excellent resulting hydrophobicity is attributed to the synergistic effects of micro/nanoroughness and low surface energy. A study of the wettability of these surfaces at temperatures ranging from 20 to-10 °C showed that the superhydrophobic surface becomes rather hydrophobic at supercooled temperatures.

Evaporative Particle Deposition on Superhydrophobic Surfaces

2013 ◽  
Author(s):  
Mercy Dicuangco ◽  
Susmita Dash ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Contact Angle ◽  
Particle Deposition ◽  
Contact Angle Hysteresis ◽  
Droplet Evaporation ◽  
Superhydrophobic Surfaces ◽  
Contact Radius ◽  
Droplet Shape ◽  
Substrate Heating ◽  
Solid Liquid ◽  
Constant Contact Angle

The ability to control the size, shape, and location of particulate deposits is important in patterning, nanowire growth, sorting biological samples, and many other industrial and scientific applications. It is therefore of interest to understand the fundamentals of particle deposition via droplet evaporation. In the present study, we experimentally probe the assembly of particles on superhydrophobic surfaces by the evaporation of sessile water droplets containing suspended latex particles. Superhydrophobic surfaces are known to result in a significant decrease in the solid-liquid contact area of a droplet placed on such a substrate, thereby increasing the droplet contact angle and reducing the contact angle hysteresis. We conduct experiments on superhydrophobic surfaces of different geometric parameters that are maintained at different surface temperatures. The transient droplet shape and wetting behavior during evaporation are analyzed as a function of substrate temperature as well as surface morphology. During the evaporation process, the droplet exhibits a constant contact radius mode, a constant contact angle mode, or a mixed mode in which the contact angle and contact radius change simultaneously. The evaporation time of a droplet can be significantly reduced with substrate heating as compared to room-temperature evaporation. To describe the spatial distribution of the particle residues left on the surfaces, qualitative and quantitative evaluations of the deposits are presented. The results show that droplet evaporation on superhydrophobic surfaces, driven by mass diffusion under isothermal conditions or by substrate heating, suppresses particle deposition at the contact line. This preempts the so-called coffee-ring and allows active control of the location of particle deposition.

scholarly journals Development of Organosilicon-Based Superhydrophobic Coatings through Atmospheric Pressure Plasma Polymerization of HMDSO in Nitrogen Plasma

Materials ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 219 ◽  
Author(s):  
Siavash Asadollahi ◽  
Jacopo Profili ◽  
Masoud Farzaneh ◽  
Luc Stafford
Keyword(s):  
Contact Angle ◽  
Atmospheric Pressure ◽  
Plasma Polymerization ◽  
Atmospheric Pressure Plasma ◽  
Plasma Jet ◽  
Nitrogen Plasma ◽  
Superhydrophobic Surfaces ◽  
Atmospheric Pressure Plasma Jet ◽  
Pressure Plasma ◽  
Superhydrophobic Coatings

Water-repellent surfaces, often referred to as superhydrophobic surfaces, have found numerous potential applications in several industries. However, the synthesis of stable superhydrophobic surfaces through economical and practical processes remains a challenge. In the present work, we report on the development of an organosilicon-based superhydrophobic coating using an atmospheric-pressure plasma jet with an emphasis on precursor fragmentation dynamics as a function of power and precursor flow rate. The plasma jet is initially modified with a quartz tube to limit the diffusion of oxygen from the ambient air into the discharge zone. Then, superhydrophobic coatings are developed on a pre-treated microporous aluminum-6061 substrate through plasma polymerization of HMDSO in the confined atmospheric pressure plasma jet operating in nitrogen plasma. All surfaces presented here are superhydrophobic with a static contact angle higher than 150° and contact angle hysteresis lower than 6°. It is shown that increasing the plasma power leads to a higher oxide content in the coating, which can be correlated to higher precursor fragmentation, thus reducing the hydrophobic behavior of the surface. Furthermore, increasing the precursor flow rate led to higher deposition and lower precursor fragmentation, leading to a more organic coating compared to other cases.

scholarly journals Water droplet friction and rolling dynamics on superhydrophobic surfaces

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Matilda Backholm ◽  
Daniel Molpeceres ◽  
Maja Vuckovac ◽  
Heikki Nurmi ◽  
Matti J. Hokkanen ◽  
...  
Keyword(s):  
Contact Angle ◽  
Friction Force ◽  
Water Droplet ◽  
Superhydrophobic Surfaces ◽  
Silicon Surfaces ◽  
Force Sensors ◽  
Water Droplets ◽  
Indirect Contact ◽  
Gold Standard Method ◽  
Superhydrophobic Coatings

Abstract Superhydrophobicity is a remarkable surface property found in nature and mimicked in many engineering applications, including anti-wetting, anti-fogging, and anti-fouling coatings. As synthetic superhydrophobic coatings approach the extreme non-wetting limit, quantification of their slipperiness becomes increasingly challenging: although contact angle goniometry remains widely used as the gold standard method, it has proven insufficient. Here, micropipette force sensors are used to directly measure the friction force of water droplets moving on super-slippery superhydrophobic surfaces that cannot be quantified with contact angle goniometry. Superhydrophobic etched silicon surfaces with tunable slipperiness are investigated as model samples. Micropipette force sensors render up to three orders of magnitude better force sensitivity than using the indirect contact angle goniometry approach. We directly measure a friction force as low as 7 ± 4 nN for a millimetric water droplet moving on the most slippery surface. Finally, we combine micropipette force sensors with particle image velocimetry and reveal purely rolling water droplets on superhydrophobic surfaces.

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