Droplet Impacting on a Hydrophobic Surface: Influence of Surface Wetting State on Droplet Behavior

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Abba Abdulhamid Abubakar ◽  
Bekir Sami Yilbas ◽  
Ghassan Hassan ◽  
Hussain Al-Qahtani ◽  
Haider Ali ◽  
...  
Keyword(s):  
Contact Angle ◽  
Hydrophobic Surface ◽  
Transition Time ◽  
Restitution Coefficient ◽  
Surface Wetting ◽  
Local Pressure ◽  
Droplet Spreading ◽  
Droplet Dynamics ◽  
Droplet Shape ◽  
Droplet Behavior

Abstract Water droplet impacting onto a hydrophobic surface is considered and the influence of the surface wetting state on the droplet dynamics is examined. Pressure variation in the impacting droplet is predicted numerically using the level set model. The droplet spreading and the retraction on the hydrophobic surface are assessed for various wetting states of the hydrophobic surface. Experiment is carried out to validate the predictions of the droplet shape and the restitution coefficient. It is found that predictions of impacting droplet shape and the restitution coefficient agree with those obtained from the experiment. The local pressure peaks formed in the droplet fluid, particularly in the retraction period, causes alteration of the droplet vertical height and the shape. Droplet spreading is influenced by the wetting state of the hydrophobic surface; hence, increasing contact angle of the hydrophobic surface lowers the spreading diameter of the droplet on the surface. The transition time of the droplet changes with the wetting state of the hydrophobic surface such that increasing droplet contact angle reduces the transition time of the droplet on the surface. The droplet remains almost round after the first bounding for large contact angle hydrophobic surface.

Dynamics of Droplet Motion Induced by Electrowetting

2016 ◽  
Author(s):  
Yi Lu ◽  
Aritra Sur ◽  
Dong Liu ◽  
Carmen Pascente ◽  
Paul Ruchhoeft
Keyword(s):  
Contact Angle ◽  
High Speed ◽  
Numerical Models ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
High Speed Photography ◽  
Droplet Dynamics ◽  
Droplet Shape ◽  
Moving Contact Line ◽  
Moving Contact

Electrowetting has drawn significant interests due to the potential applications in electronic displays, lab-on-a-chip devices and electro-optical switches, etc. Current understanding of electrowetting-induced droplet dynamics is hindered by the inadequacy of available numerical and theoretical models in properly handling the dynamic contact angle at the moving contact line. A combined numerical and experimental approach was employed in this work to study the spatiotemporal responses of a droplet subject to EW with both direct current and alternating current actuating signals. The time evolution of the droplet shape was measured using high-speed photography. Computational fluid dynamics models were developed by using the Volume of Fluid-Continuous Surface Force method in conjunction with a selected dynamic contact angle model. It was found that the numerical models were able to accurately predict the key parameters of the electrowetting-induced droplet dynamics.

Impact Characteristics of a Carbonated Water Droplet On Hydrophobic Surface

2021 ◽  
Author(s):  
Abba Abdulhamid Abubakar ◽  
Bekir Sami Yilbas ◽  
Hussain Al-Qahtani
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Gas Bubbles ◽  
Hydrophobic Surface ◽  
Restitution Coefficient ◽  
Droplet Spreading ◽  
Co2 Gas ◽  
Carbonated Water ◽  
Bubble Sizes ◽  
Spreading Rates

Abstract Carbonated water drops impact on a hydrophobic surface is examined. The influence of CO2 gas bubbles in droplet fluid on impacting droplet characteristics, such as spreading rates and restitution coefficient, are explored. The predictions of droplet wetting diameter and spreading rates are validated through the experimental data obtained from high-speed recording. The findings reveal that predictions agree well with the experimental data. CO2 gas bubbles in the droplet are compressed by the total impact pressure of the droplet liquid while slightly reducing the gas bubble sizes. The small size of close by bubbles at high pressure can merge forming large size bubbles, which occur towards the end of droplet spreading and retraction periods. The pressure increase in the fluid gives rise to increased vertical height of the droplet and slightly reduces the droplet contact diameter on the impacted surface. The work done during the compression of CO2 gas in bubbles lowers the restitution coefficient of the droplet after the retraction period.

scholarly journals An Analytical Two-Dimensional Linearized Droplet Shape Model for Combined Tangential and Normal Body Forces

2020 ◽  
Vol 4 (3) ◽  
pp. 35 ◽  
Author(s):  
Margaritis Kostoglou ◽  
Thodoris D. Karapantsios
Keyword(s):  
Present Model ◽  
Two Dimensional ◽  
Shape Features ◽  
Droplet Spreading ◽  
Shape Model ◽  
Droplet Shape ◽  
Final Model ◽  
Droplet Behavior ◽  
Applied Forces ◽  
Range Of Values

In view of emerging research on forced wetting under complex applied forces, a simple model for a droplet shape evolution is developed here. In particular, the model refers to droplet spreading under quasisteady conditions. The corresponding linearized two-dimensional Young–Laplace equation is solved analytically resulting in a system of two equations that relates the droplet shape features to each other. Despite its simplicity, the final model produces a wealth of droplet behaviors when combined with the physical requirement that the contact angle should be within a particular range of values. Indicative results of the droplet behavior under several forces scenarios are examined here exhibiting why the present model is useful for designing experimental campaigns on forced spreading.

Numerical Simulation of Droplet Impact on an Isothermal Micro-Grooved Solid Surface

2010 ◽  
Author(s):  
Yujia Tao ◽  
Xiulan Huai ◽  
Zhigang Li
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Solid Surface ◽  
Initial Velocity ◽  
Surface Tension Coefficient ◽  
Liquid Region ◽  
Spreading Factor ◽  
Droplet Spreading ◽  
Droplet Dynamics ◽  
The Impact

The process of a micro droplet of distilled water impact on an isothermal micro-grooved solid surface is numerical simulated in this paper. To accurately represent the droplet dynamics, special attention is given to the variation of the droplet pressure and velocity, the movement of the free surface between two fluids and the deforming of the droplet after impact. The Volume Of Fluid method is used to track the position and the shape of the liquid region. The PISO algorithm is selected to solve the pressure-velocity coupling. The influences of the droplet initial velocity, the contact angle for water on the surface perpendicular to the groove direction and the surface tension coefficient on the impact process are discussed in detail. The results show that the droplet spreading factor improves notably with the increase of the initial velocity, and reduces with the increase of the contact angle. When the surface tension coefficient increases, the spreading factor reduces greatly. The spreading factor is the largest and the time elapsing is the longest in the case of σ = 0.038 N/m.

Droplet Shapes on Superhydrophobic Surfaces Under Electrowetting Actuation

2011 ◽  
Author(s):  
S. Ravi Annapragada ◽  
Jayathi Y. Murthy ◽  
Suresh V. Garimella
Keyword(s):  
Contact Line ◽  
Intermediate Energy ◽  
Contact Angles ◽  
Superhydrophobic Surfaces ◽  
Droplet Dynamics ◽  
Droplet Shape ◽  
Structured Surfaces ◽  
Droplet Behavior ◽  
Wetting Process ◽  
Contact Line Friction

Droplet behavior on structured surfaces has recently generated a lot of interest due to its application to self-cleaning surfaces and in microfluidic devices. In this paper, the droplet shape and the droplet state on superhydrophobic surfaces are predicted using the Volume of Fluid (VOF) approach. Various structured surfaces are considered and the apparent contact angles are extracted from the predicted droplet shapes. Droplet dynamics under electrowetting are also modeled, including contact line friction. The model is validated against in-house experiments and experiments from the literature. The droplet state, droplet shape and apparent contact angles match well with the experimental measurements. The Cassie and Wenzel states on structured surfaces are also accurately predicted. Further, the electrowetting-induced transition from the Cassie to the Wenzel state and the reversal to the Cassie state is predicted for two different superhydrophobic surfaces. The transient wetting process, intermediate energy states and droplet shapes during electrowetting are simulated. The effective contact line friction coefficient on pillared surfaces is predicted to be 0.14 Ns/m2, consistent with published values.

Osteoconductivity of Superhydrophilic Ti- and Zr-Alloy for Biomedical Application

2016 ◽  
Vol 879 ◽  
pp. 2524-2527
Author(s):  
Masazumi Okido ◽  
Kensuke Kuroda
Keyword(s):  
Contact Angle ◽  
Water Contact Angle ◽  
Strong Influence ◽  
Biomedical Application ◽  
Hydrophobic Surface ◽  
Hydrophilic Surface ◽  
Water Contact ◽  
Zr Alloy ◽  
Zr Alloys

Surface hydrophilicity is considered to have a strong influence on the biological reactions of bone-substituting materials. However, the influence of a hydrophilic or hydrophobic surface on the osteoconductivity is not completely clear. In this study, we produced super-hydrophilic and hydrophobic surface on Ti-and Zr-alloys. Hydrothermal treatment at 180 oC for 180 min. in the distilled water and immersion in x5 PBS(-) brought the super-hydrophilic surface (water contact angle < 10 (deg.)) and heat treatment of as-hydrothermaled the hydrophobic surface. The osteoconductivity of the surface treated samples with several water contact angle was evaluated by in vivo testing. The surface properties, especially water contact angle, strongly affected the osteoconductivity and protein adsorbability, and not the surface substance.

Modeling of Transport During Droplet Deposition and Spreading on Smooth and Microstructured Superhydrophilic Surfaces

2016 ◽  
Author(s):  
Jordan P. Mizerak ◽  
Van P. Carey
Keyword(s):  
Contact Angle ◽  
Contact Angles ◽  
Ansys Fluent ◽  
Effective Contact ◽  
Microstructured Surfaces ◽  
Static Contact ◽  
Droplet Behavior ◽  
Contact Line Pinning ◽  
The Impact ◽  
Superhydrophilic Surfaces

The dynamic behavior of impinging water droplets is studied in the context of varying surface morphologies on smooth and microstructured superhydrophilic surfaces. The goal of this study is to evaluate the capability of contact angle wall adhesion models to accurately produce spreading phenomena seen on a variety of surface types. We analyze macroscale droplet behavior, specifically spreading extent and impinging regime, in situations of varying microscale wetting character and surface morphology. Axisymmetric, volume of fluid (VOF) simulations with static contact angle wall adhesion are conducted in ANSYS Fluent. Simulations are performed on water for low Weber numbers (We<20) on surfaces with features of length scale 5–10μm. Advanced microstructured surfaces consisting of unique wetting characteristics and lengths on each face are also tested. Results show that while the contact angle wall adhesion model shows fair agreement for conventional surfaces, the model underestimates spreading by over 60% for surfaces exhibiting estimated contact angles below approximately 0.5°. Microstructured surfaces adapt the wetting behavior of smooth surfaces with higher effective contact angles based on contact line pinning on morphology features. The propensity of the model to produce Wenzel and Cassie-Baxter states is linked to the spreading radius, introducing an interdependency of microscale wetting and macroscale spreading behavior. Conclusions describing the impact of results on evaporative cooling are also discussed.

scholarly journals Superhydrophobic textile: treatment in aqueous solutions of aluminum salts

2021 ◽  
Author(s):  
Eterina Endiiarova ◽  
Artem Osipov ◽  
Sergey Alexandrov ◽  
Alexander Shakhmin
Keyword(s):  
Contact Angle ◽  
Photoelectron Spectroscopy ◽  
Superhydrophobic Surface ◽  
Hydrophobic Surface ◽  
Solution Concentration ◽  
Textile Processing ◽  
X Ray ◽  
Textile Materials ◽  
Aluminum Salts ◽  
Processing Treatment

Abstract Textile is currently a promising material. Obtaining hydrophobic surfaces on textiles significantly increases its value when used in various fields. In this work we carried out experiments on textile processing. Treatment of textile materials in solutions containing aluminum allows to obtain a superhydrophobic surface. KAl(SO4) and AlCl3 solutions were used. It was found that treatment in AlCl3 solution is more effective and allows to achieve a hydrophobic surface on textile with a contact angle of more than 150º. The hydrophobic surface retained its properties even after 30 days. Textile samples were investigated using X-Ray photoelectron spectroscopy (XPS). The X-Ray photoelectron spectroscopy results showed hydrophobicity in the treatment of textile materials is ensured by the formation of aluminum oxide on the surface. The dependence of the coarse calico contact angle on the AlCl3 solution concentration is determined. which demonstrates that when the concentration of AlCl3 solution increases (within the limits of variation considered), the contact angle also increases.

scholarly journals Effect of Nanoparticles on Wettability of Nanocoating on Carbon Steel

2016 ◽  
Vol 1 (2) ◽  
pp. 71-74
Author(s):  
Norhasnidawani Johari ◽  
Noor Azlina Hassan ◽  
Norita Hassan ◽  
Mohd Hanafi Ani
Keyword(s):  
Contact Angle ◽  
Carbon Steel ◽  
Metal Oxide ◽  
Water Drop ◽  
Metal Oxide Nanoparticles ◽  
Sol Gel ◽  
Hydrophobic Surface ◽  
Oxide Nanoparticles ◽  
Water Medium ◽  
Wetting Ability

Nanocoatings plays an important role in coating industry. The solution was being prepared through copolymerization of epoxy resin hardener and with the incorporation of metal oxide nanoparticles, Zinc Oxide (ZnO) and Silica (SiO2). ZnO and SiO2 were synthesized using sol-gel. Epoxy hardener acted as host while the metal oxide nanoparticles as guest components. The formulation of nanocoatings with excellent adhesion strength and corrosion protection of carbon steel was studied. The performance of wetting ability with different medium was analysed using contact angle. Water medium showed the addition of 3wt% of hybrid between ZnO and SiO2 was the best nanocoating to form hydrophobic surface and was also the best nanocoating surface to form hydrophilic surface with vacuum oil dropping. In oil dropping, the contact angle was smaller than 90° and the water drop tends to spreads on surface.

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