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.

Facile Fabrication of Fluorine-Free Superhydrophobic Surfaces with SiO2 Monospheres

2021 ◽  
Vol 16 (2) ◽  
pp. 208-212
Author(s):  
Zhong-Peng Liu ◽  
Si-Nan Song ◽  
Mu Zhang
Keyword(s):  
Contact Angle ◽  
Superhydrophobic Surface ◽  
Hydrophobic Surface ◽  
Silica Particles ◽  
Superhydrophobic Surfaces ◽  
Particle Sizes ◽  
Stöber Method ◽  
Spherical Silica ◽  
Spherical Silica Particles ◽  
Facile Fabrication

Recently, superhydrophobic surface on various type of substrates have attracted much attentions in electronics field. In this work, the classic Stöber method was used to prepare spherical silica particles with different particle sizes by adding different amounts of electrolyte (potassium chloride), giving rise to size distribution ranging from 300 nm to 2.55 yitm. Herein we constructed a micro-nano lotus-like structure in a facile way, achieving a superhydrophobic surface with using any Fluorine related chemicals. In the sense, the silica particles modified with HMDS were sprayed to prepare hydrophobic surface with contact angle up to 152.96° by increasing the frequency of sprays.

Using Superhydrophobic SU-8 Film as the Dielectric for Electrowetting-on-Dielectric

2018 ◽  
Vol 281 ◽  
pp. 604-609
Author(s):  
Yu Hao Piao ◽  
Wei Qiang Wang
Keyword(s):  
Contact Angle ◽  
Dielectric Layer ◽  
Superhydrophobic Surface ◽  
High Performance ◽  
Apparent Contact Angle ◽  
Experimental Results ◽  
Electrowetting On Dielectric ◽  
Dc Voltage ◽  
Theoretical Predictions ◽  
Good Agreement

In this paper, we study the electrowetting effect of superhydrophobic SU-8 film as the dielectric for Electrowetting-on-Dielectric (EWOD). The change of apparent contact angle (APCA) on superhydrophobic surface in electrowetting systems was measured and analyzed using a modified Lippmann-Yong equation. The variation of APCA between droplet and device surface under various DC voltage and AC voltage of different frequencies was fully experimented. The experimental results were in good agreement with the theoretical predictions. This study shows the potential of using superhydrophobic SU-8 film as the dielectric layer in high-performance EWOD devices.

A Two-Step Method to Prepare Stable Superhydrophobic Surface on Steel Substrates

2012 ◽  
Vol 463-464 ◽  
pp. 349-353 ◽  
Author(s):  
Feng Guo ◽  
Xun Jia Su ◽  
Gen Liang Hou ◽  
Zhao Hui Liu ◽  
Hai Peng Jia
Keyword(s):  
Contact Angle ◽  
Superhydrophobic Surface ◽  
Low Cost ◽  
Superhydrophobic Surfaces ◽  
Step Method ◽  
Water Contact ◽  
Lotus Leaf ◽  
Nanoscale Particles ◽  
Steel Substrates

Superhydrophobic surfaces have been a hot topic during the last decade owing to their great potential in widely application. In this work, we report on a facile and low-cost two-step method to fabricate superhydrophobic surface on steel substrates. The as-obtained surface shows an interesting hierarchical structure composed of microscale flowerlike cluster and nanoscale particles, which is similar to that of a lotus leaf. After further modification with stearic acid, the resultant surface exhibits remarkable superhydrophobic properties. The water contact angle is as high as 155°. Moreover, the superhydrophobic properties are long-term stable.

scholarly journals Robust Superhydrophobic Surface on Polypropylene with Thick Hydrophobic Silica Nanoparticle-Coated Films Prepared by Facile Compression Molding

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3155
Author(s):  
Oyunchimeg Erdene-Ochir ◽  
Doo-Man Chun
Keyword(s):  
Contact Angle ◽  
Surface Energy ◽  
Alkaline Medium ◽  
Superhydrophobic Surface ◽  
Thick Layer ◽  
Scratch Test ◽  
Superhydrophobic Surfaces ◽  
Sliding Angle ◽  
Hydrophobic Silica ◽  
Low Surface Energy

Superhydrophobic surfaces have been extensively studied for their unique interfacial interaction between water and the surface, and they can be used for self-cleaning, drag reduction, anti-icing, and other applications. To make the superhydrophobic surfaces, nano/microscale structures and a low surface energy should be realized. The development of a durable superhydrophobic surface was hindered by the vulnerability of the surface to mechanical contact. To improve the robustness of the superhydrophobic surface toward mechanical damage, the hydrophobic polypropylene (PP) surface was coated with a thick layer of hydrophobic silica nanoparticles (SNPs) using a simple compression molding process. The thick layer consists of SNPs and PP, and the roles of SNPs and PP are nano/microscale structures with a low surface energy and binder for nanoparticles, respectively. This revealed improvement in the superhydrophobic tendency, with an apparent contact angle of about 170° and a sliding angle of less than 5°. The morphology and the corresponding elemental analysis of the PP/SNPs coated films were investigated using field emission scanning electron microscopy and energy-dispersive spectrometry. The mechanical durability of the superhydrophobic surface was evaluated by the scotch tape test and scratch test with sandpaper. The coated films with SNPs showed the superhydrophobic behavior after 25 tape tests. In addition, the coated films with SNPs showed a contact angle greater than 150° and a sliding angle less than 10° after a 100-cm scratch test with 1000 grit sandpaper, under a weight of 500 g, on an area of 40 × 40 mm2. The chemical stability of PP/SNPs coated films was also investigated in acidic, neutral, and alkaline medium solutions. The films showed good stability under the acidic and neutral medium solutions even after 24 h, but an alkaline medium could damage the surface. The obtained results demonstrated the robustness of the superhydrophobic coating with SNPs.

scholarly journals Facile Electrochemical Method for the Fabrication of Stable Corrosion-Resistant Superhydrophobic Surfaces on Zr-Based Bulk Metallic Glasses

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1558
Author(s):  
Mengmeng Yu ◽  
Ming Zhang ◽  
Jing Sun ◽  
Feng Liu ◽  
Yujia Wang ◽  
...  
Keyword(s):  
Contact Angle ◽  
Corrosion Resistance ◽  
Surface Energy ◽  
Metallic Glasses ◽  
Composite Structures ◽  
Superhydrophobic Surface ◽  
Electrochemical Method ◽  
Electrochemical Etching ◽  
Superhydrophobic Surfaces ◽  
Nano Composite

Both surface microstructure and low surface energy modification play a vital role in the preparation of superhydrophobic surfaces. In this study, a safe and simple electrochemical method was developed to fabricate superhydrophobic surfaces of Zr-based metallic glasses with high corrosion resistance. First, micro–nano composite structures were generated on the surface of Zr-based metallic glasses by electrochemical etching in NaCl solution. Next, stearic acid was used to decrease surface energy. The effects of electrochemical etching time on surface morphology and wettability were also investigated through scanning electron microscopy and contact angle measurements. Furthermore, the influence of micro–nano composite structures and roughness on the wettability of Zr-based metallic glasses was analysed on the basis of the Cassie–Baxter model. The water contact angle of the surface was 154.3° ± 2.2°, and the sliding angle was < 5°, indicating good superhydrophobicity. Moreover, the potentiodynamic polarisation test and electrochemical impedance spectroscopy suggested excellent corrosion resistance performance, and the inhibition efficiency of the superhydrophobic surface reached 99.6%. Finally, the prepared superhydrophobic surface revealed excellent temperature-resistant and self-cleaning properties.

Preparation of Superhydrophobic Surface on Copper Foils by a Facile Method

2013 ◽  
Vol 834-836 ◽  
pp. 42-45
Author(s):  
Zhi Qing Yuan ◽  
Xian Wang ◽  
Ji Ping Bing ◽  
Meng Lei Wang ◽  
Juan Huang
Keyword(s):  
Contact Angle ◽  
Superhydrophobic Surface ◽  
Solution Concentration ◽  
Copper Surface ◽  
Ethanol Solution ◽  
Superhydrophobic Surfaces ◽  
Sliding Angle ◽  
Water Contact ◽  
Copper Foils ◽  
Immersing Method

In the paper, we prepared superhydrophobic surfaces on copper foils via a facile solution-immersing method. The influence of experiment conditions, such as solution concentration, immersing time and temperature, on the surface structure is investigated in detail. When the concentration of stearic acid-ethanol solution, the immersing time and the temperature are 2 g/L, 120 min and 40°,respectively, the resulting copper surface possesses great superhydrophobicity with a water contact angle of up to 159° and a sliding angle of only 3°.

scholarly journals Investigation of Coalescence-Induced Droplet Jumping on Mixed-Wettability Superhydrophobic Surfaces

Processes ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 142
Author(s):  
Ming-Jun Liao ◽  
Li-Qiang Duan
Keyword(s):  
Contact Angle ◽  
Simulation Method ◽  
Strip Width ◽  
Superhydrophobic Surfaces ◽  
Dynamics Simulation ◽  
Periodic Strip ◽  
Mixed Wettability ◽  
Potential Applications ◽  
The Difference ◽  
The One

Coalescence-induced droplet jumping has received more attention recently, because of its potential applications in condensation heat transfer enhancement, anti-icing and self-cleaning, etc. In this paper, the molecular dynamics simulation method is applied to study the coalescence-induced jumping of two nanodroplets with equal size on the surfaces of periodic strip-like wettability patterns. The results show that the strip width, contact angle and relative position of the center of two droplets are all related to the jumping velocity, and the jumping velocity on the mixed-wettability superhydrophobic surfaces can exceed the one on the perfect surface with a 180° contact angle on appropriately designed surfaces. Moreover, the larger both the strip width and the difference of wettability are, the higher the jumping velocity is, and when the width of the hydrophilic strip is fixed, the jumping velocity becomes larger with the increase of the width of the hydrophobic strip, which is contrary to the trend of fixing the width of the hydrophobic strip and altering the other strip width.

Fabrication of Superhydrophobic Surface by Modulating Morphology of the Organogel

Soft Matter ◽  
2021 ◽  
Author(s):  
Jianchen Zhu ◽  
Tian ren Zhang ◽  
Yajie Liu ◽  
Daoyi Lu ◽  
Peng Zhang ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Superhydrophobic Surface ◽  
Superhydrophobic Surfaces ◽  
Low Molecular Weight

A kind of low-molecular weight organic gelator (LMOG) bearing hydrazine linkage and end-capped by alkoxy-substituted phenyl, namely 1, 4-bis[(3, 4-bisoctyloxyphenyl)hydrozide]phenylene (BPH-8), was used to facilely fabricate superhydrophobic surfaces by drop-casting...

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