scholarly journals Enhancement of Sensitivity and Accuracy of Micro/Nano Water Droplets Detection Using Galvanic-Coupled Arrays

Sensors ◽  
2019 ◽  
Vol 19 (20) ◽  
pp. 4500 ◽  
Author(s):  
Rekha Goswami Shrestha ◽  
Tatsuya Ando ◽  
Yukihiro Sakamoto ◽  
Jin Kawakita
Keyword(s):  
Contact Angle ◽  
Water Droplet ◽  
High Speed ◽  
Current Response ◽  
Water Droplets ◽  
Galvanic Current ◽  
Moisture Sensor ◽  
Average Value ◽  
Small Water ◽  
Working Principle

A moisture sensor has been reported that detects invisibly small water droplets and distinguishes their particle size with high accuracy and high speed. This sensor uses narrow lines of dissimilar metals as electrodes, arranged with gaps of 0.5 to 10 μm. The working principle for this sensor is that it measures the galvanic current generated when a water droplet forms a bridge-like structure between the electrodes. In addition, the surface of the sensor was controlled by using hydrophilic polymer, GL, and hydrophobic polymer, PMMA. The study of the relationship between the contact angle, projected area of water droplets and current response from the sensor with a modified surface showed that in the case of GL, the contact angle was small (wettability increased) and the average value and distribution of the projected water droplet area and the sensor’s response increased. This enhanced the sensor’s sensitivity. On the other hand, in the case of PMMA, the contact angle was large (wettability decreased), the area of the water droplet and its distribution became small and the accuracy of discriminating the water droplet’s diameter by the sensor enhanced. Therefore, by rendering sensor’s surface hydrophilic and hydrophobic, the sensitivity and accuracy of the sensor could be enhanced.

Molecular Simulation of the Contact Angle of Water Droplet on a Platinum Surface

2005 ◽  
Author(s):  
Bo Shi ◽  
Shashank Sinha ◽  
Vijay K. Dhir
Keyword(s):  
Contact Angle ◽  
Molecular Simulation ◽  
Simulation Study ◽  
Water Droplet ◽  
Solid Wall ◽  
Contact Angles ◽  
Water Droplets ◽  
Platinum Surface

This paper presents a molecular simulation study of the contact angles of water droplets on a platinum surface for a range of temperatures. SPC/E and Z-P model are used for the water-water and water-platinum potentials, respectively. The results show that the contact angle decreases with the increase of system temperatures and increases when the potential decreases. When the temperature is high enough, the contact angles drop to zero degrees. The results were compared with the argon-virtual solid wall and water-Aluminum results, a similar trend was found.

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.

scholarly journals Stretchable Hydrophobic Surfaces and Self-Cleaning Applications

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Bekir Sami Yilbas ◽  
Ghassan Hassan ◽  
Hussain Al-Qahtani ◽  
Naser Al-Aqeeli ◽  
Abdullah Al-Sharafi ◽  
...  
Keyword(s):  
Contact Angle ◽  
Water Droplet ◽  
Dust Removal ◽  
Dust Particles ◽  
Mass Ratio ◽  
Water Droplets ◽  
Surface Wetting ◽  
Hydrophobic Surfaces ◽  
Removal Mechanisms ◽  
Nano Size

Abstract Hydrophobizing of stretchable elastomer surfaces is considered and the reversible behavior of the resulting surface wetting state is examined after stretching and relaxing the hydrophobized samples. The environmental dust are analyzed in terms of elemental constitutes and size, and the dust pinning on the hydrophobized surface is measured. The dust removal mechanisms, by the water droplets on the hydrophobized surface, are investigated. We demonstrated that deposition of functionalized nano-size silica units on the elastomer surface gives rise to hydrophobicity with 135° ± 3° contact angle and low hysteresis of 3° ± 1°. Stretching hydrophobized elastomer surface by 50% (length) reduces the contact angle to 122° ± 3° and enhances the hysteresis to 6° ± 1°. However, relaxing the stretched sample causes exchanging surface wetting state reversibly. Water droplet rolling and sliding can clean the dusty hydrophobized surface almost 95% (mass ratio of the dust particles removed). Droplet puddling causes striations like structures along the droplet path and close examination of the few residues of the dust reveals that the droplet takes away considerably large amount of dust from surface.

Dynamic Behavior of a Small Water Droplet Impact Onto a Heated Hydrophilic Surface

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
El-Sayed R. Negeed ◽  
M. Albeirutty ◽  
Sharaf F. AL-Sharif ◽  
S. Hidaka ◽  
Y. Takata
Keyword(s):  
Dynamic Behavior ◽  
Water Droplet ◽  
High Speed ◽  
Heated Surface ◽  
Droplet Diameter ◽  
Video Camera ◽  
Surface Wettability ◽  
Hydrodynamic Characteristics ◽  
Small Water ◽  
Hot Surface

The aim of this study is to investigate the influence of the surface wettability on the dynamic behavior of a water droplet impacting onto a heated surface made of stainless steel grade 304 (Sus304). The surface wettability is controlled by exposing the surfaces to plasma irradiation for different time periods (namely, 0.0, 10, 60, and 120 s). The experimental runs were carried out by spraying water droplets on the heated surface where the droplet diameter and velocity were independently controlled. The droplet behavior during the collision with the hot surface has been recorded with a high-speed video camera. By analyzing the experimental results, the effects of surface wettability, contact angle between impacting droplet and the hot surface, droplet velocity, droplet size, and surface superheat on the dynamic behavior of the water droplet impacting on the hot surface were investigated. Empirical correlations are presented describing the hydrodynamic characteristics of an individual droplet impinging onto the heated hydrophilic surfaces and concealing the affecting parameters in such process.

Liquid marble and water droplet interactions and stability

Soft Matter ◽  
2015 ◽  
Vol 11 (39) ◽  
pp. 7728-7738 ◽  
Author(s):  
Kazuyuki Ueno ◽  
Ghislain Bournival ◽  
Erica J. Wanless ◽  
Saori Nakayama ◽  
Emma C. Giakoumatos ◽  
...  
Keyword(s):  
Water Droplet ◽  
High Speed ◽  
Video Camera ◽  
Water Droplets ◽  
High Speed Video ◽  
High Speed Video Camera ◽  
Liquid Marble

The interactions between two individual water droplets were investigated in air using a combination of coalescence rig and high speed video camera.

Sessile-Water-Droplet Contact Angle: the Effect of Adsorption

2010 ◽  
Author(s):  
H. Ghasemi ◽  
C. A. Ward
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Closed System ◽  
Water Droplet ◽  
Line Tension ◽  
Water Droplets ◽  
Three Phase ◽  
To Come ◽  
Predicted Values ◽  
Solid Liquid

A method has been recently proposed for determining the surface tension of solid-vapor interfaces. The proposed method was used in conjunction with Gibbsian thermodynamics to investigate both analytically and experimentally the possible role of line tension in determining the contact angle of sessile-water-droplets. After forming a sessile-water-droplet in a closed system, its contact angle was determined by measuring the curvature of three-phase contact line and the height of the axisymmetric droplet on its centerline. The total number of the moles in the closed system was determined from the minimum in the Helmholtz function. The total number of moles in the system was then changed to a new value and the system allowed to come to equilibrium again. The contact angle in the new equilibrium condition could be measured and predicted by taking the adsorption at the solid-liquid and solid-vapor interfaces into account but with line tension completely neglected. The predicted values of contact angle are in closed agreement with those measured indicating line tension plays no role in determining the contact angle of mm-sized water droplets on a polished Cu surface. The surface tension of the solid-vapor interface was approximately constant and equal to the surface tension of adsorbing fluid; that is, the Young equation could be simplified.

scholarly journals PAPER STRAWS: AN INVESTIGATION INTO SURFACE MODIFICATION AND HYDROPHOBIZATION OF CELLULOSE

2020 ◽  
pp. 1-10
Author(s):  
Norbert Banyi ◽  
Jordan Hassett
Keyword(s):  
Contact Angle ◽  
Surface Modification ◽  
Water Droplet ◽  
Contact Angles ◽  
Water Droplets ◽  
Treatment Groups ◽  
Angle Measurements ◽  
Contact Angle Measurements ◽  
Silylation Reaction

In order to improve the quality of paper straws, experiments involving the hydrophobization of paper, in a silylation reaction with chloro(dimethyl)octadecylsilane using various solvents, were conducted. The ImageJ program was used to quantify hydrophobicity by calculating the contact angle between a water droplet and a small piece of paper, which were compared between treatment groups as well as with untreated paper and plastic straws. Samples were exposed to a variety of liquids in one-hour periods for a total of six hours. After each hour, contact angle measurements were taken. Results suggested that hydrophobicity declines with time due to leaching of silanol from the treated paper. Contact angles between water droplets and the treated paper remained larger than that of untreated paper straws throughout testing, indicating higher hydrophobicity. Furthermore, samples that were silylated using dioxane as a solvent were better able to maintain hydrophobicity than samples silylated using toluene as a solvent.

Experimental Studies of Liquid Water Droplet Growth and Instability at the Gas Diffusion Layer/Gas Flow Channel Interface

2005 ◽  
Author(s):  
Michael A. Hickner ◽  
Ken S. Chen
Keyword(s):  
Contact Angle ◽  
Diffusion Layer ◽  
Liquid Water ◽  
Water Droplet ◽  
Gas Flow ◽  
Contact Angle Hysteresis ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Flow Channel ◽  
Water Droplets

Experimental investigations were carried out to visualize the dynamic behavior (contact angle hysteresis and droplet shape) of liquid water droplets on carbon paper gas diffusion layers that are typically employed in proton exchange membrane fuel cells (PEMFCs). The experimental technique mimicks the generation of liquid water and formation of droplets in an air shear flow at the gas diffusion layer – gas flow channel interface of a simulated PEMFC cathode. Images obtained of growing liquid water droplets yield information on the contact angle hysteresis and droplet height, which were subsequently used to map droplet “instability” diagrams. These instability diagrams provide quantitative guidance on liquid water droplet removal at the gas diffusion layer/gas flow channel interface under the conditions of interest. The experimentally mapped droplet diagrams are compared with those predicted using a simplified model based on a macroscopic force balance and reasonably good agreement is obtained.

Separating Wickability and Wetting Effects During Water Droplet Evaporation on Superhydrophilic Nanoporous Surfaces

2019 ◽  
Author(s):  
Alanna Y. Cooney ◽  
Emma R. McClure ◽  
Samuel Cabrera ◽  
Van P. Carey
Keyword(s):  
Contact Angle ◽  
Impact Velocity ◽  
High Speed ◽  
Experimental Results ◽  
Nanostructured Surface ◽  
Water Droplets ◽  
Droplet Spreading ◽  
Wetting Contact Angle ◽  
Vof Model ◽  
Nanoporous Surfaces

Abstract The dynamic behavior of impinging water droplets is studied in the context of varying surface wettability and wickability on smooth and nanostructured superhydrophilic surfaces. This study distinguishes the separate effects of wetting (contact angle), wickability, and inertia on the spreading and vaporization of water droplets deposited on nanoporous surfaces by considering experimental results in tandem with axisymmetric, volume of fluid (VOF) simulations of droplet spreading. High speed videos were obtained for water droplets spreading on nanoporous surfaces which exhibit very low (< 15°) contact angle and high wickability. In this study, the effect of wickability was assessed by comparing the experimental results, which include the low contact angle and high wickability effects, to predictions of the VOF model, which include only the ultralow contact angle. While a droplet touched to the nanostructured surface demonstrates spreading driven by wicking, droplets which hit the surface with a non-zero impact velocity demonstrate spreading characteristics similar to the smooth surface, which are driven by inertia and ultra-low contact angle. The presence of the nanoporous layer impacts the equilibrium position of the contact line and the final spread radius changes with impact velocity on the nanostructured surface. These results provide fundamental input for modeling of spray cooling systems with nanostructured surfaces.

Effects of Ambient Air Relative Humidity and Surface Temperature on Water Droplet Spreading Dynamics

2018 ◽  
Author(s):  
M. Jadidi ◽  
M. A. Farzad ◽  
J. Y. Trepanier ◽  
A. Dolatabadi
Keyword(s):  
Contact Angle ◽  
Relative Humidity ◽  
Surface Temperature ◽  
Air Temperature ◽  
Water Droplet ◽  
Superhydrophobic Surface ◽  
High Speed ◽  
Ambient Air ◽  
Dew Point ◽  
Droplet Spreading

Water droplet impact on horizontal glass, aluminum, and superhydrophobic surfaces is experimentally investigated using high speed imaging. Experiments are performed at three different relative humidities (i.e. 10, 20 and 30%) and three surface temperatures (i.e. 20, 2 and −2°C) to ascertain their effects on droplet spreading and recoil behaviors. In this study, the droplet Weber number, Reynolds number, and the ambient air temperature are fixed at 16.2, 1687, and 23°C, respectively. The high-speed images of impact, spreading and recoil of the droplets as well as the temporal variations of droplet spreads are prepared. Results show that the ratio of surface temperature to dew point temperature (which depends on the air temperature and relative humidity) has a significant influence on droplet spreading, recoil, and contact angle. When this ratio is less than one, condensation and frost formation become important. Decreasing the mentioned ratio (it can be done by decreasing the surface temperature or increasing the relative humidity) causes the droplet spreading factor for hydrophilic surfaces to increase significantly. For superhydrophobic surface, decreasing this ratio (within the mentioned range) does not influence the maximum spreading. However, the recoiling phase is slowed down and the droplet detachment time form the superhydrophobic surface is increased noticeably. In addition, the equilibrium contact angle decreases as the mentioned ratio decreases.

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