Effect of Electrode Shape on Droplet Actuation in Electrowetting-Based Microfluidics

2008 ◽  
Author(s):  
Negar Rajabi ◽  
Ali Dolatabadi
Keyword(s):  
Contact Angle ◽  
Electric Field ◽  
Laplace Equation ◽  
Volume Of Fluid ◽  
Superior Performance ◽  
Angle Distribution ◽  
Phase Line ◽  
Electrode Shape ◽  
Three Phase ◽  
Droplet Morphology

This article describes the effect of electrode shape in electrowetting-based droplet actuation. A Volume of Fluid technique is applied to track the 3-D interface. The Laplace equation is solved to predict the time and space dependent electric field in the domain. The onset of actuation, contact angle distribution at the three phase line, and the droplet morphology are studied for two electrode shapes; i.e. flat and crescent. The acceleration and the velocity of the droplet are also other important parameters to show the superior performance of crescent electrode in droplet actuation.

Dependence of the Contact Angle on Adsorption at the Solid-Liquid Interface

2010 ◽  
Author(s):  
C. A. Ward
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Pressure Range ◽  
Line Tension ◽  
Liquid Interface ◽  
Fluid Interfaces ◽  
Phase Line ◽  
Three Phase ◽  
Solid Liquid Interface ◽  
Solid Liquid

A method for determining the surface tension of solid-fluid interfaces has been proposed. For a given temperature and fluid-solid combination, these surface tensions are expressed in terms of material properties that can be determined by measuring the amount of vapor adsorbed on the solid surface as a function of xV, the ratio of the vapor-phase pressure to the saturation-vapor pressure. The thermodynamic concept of pressure is shown to be in conflict with that of continuum mechanics, but is supported experimentally. This approach leads to the prediction that the contact angle, θ, can only exist in a narrow pressure range and that in this pressure range, the solid-vapor surface tension is constant and equal to the surface tension of the liquid-vapor interface, γLV. The surface tension of the solid-liquid interface, γSL, may be expressed in terms of measurable properties, γLV and θ: γSL = γLV(1 − cosθ). The value of θ is predicted to depend on both the pressure in the liquid at the three-phase, line x3L, and the three-phase line curvature, Ccl. We examine these predictions using sessile water droplets on a polished Cu surface, maintained in a closed, constant volume, isothermal container. The value of θ is found to depend on the adsorption at the solid-liquid interface, nSL = nSL(x3L,Ccl). The predicted value of θ is compared with that measured, and found to be in close agreement, but no effect of line tension is found.

scholarly journals Collembola cuticles and the three-phase line tension

2017 ◽  
Vol 8 ◽  
pp. 1714-1722 ◽  
Author(s):  
Håkon Gundersen ◽  
Hans Petter Leinaas ◽  
Christian Thaulow
Keyword(s):  
Contact Angle ◽  
Surface Structure ◽  
Large Change ◽  
Line Tension ◽  
Contact Angles ◽  
Surface Structures ◽  
Exposed Surface ◽  
Phase Line ◽  
Three Phase ◽  
Cuticular Surface

The cuticles of most springtails (Collembola) are superhydrophobic, but the mechanism has not been described in detail. Previous studies have suggested that overhanging surface structures play an important role, but such structures are not a universal trait among springtails with superhydrophobic cuticles. A novel wetting experiment with a fluorescent dye revealed the extent of wetting on exposed surface structures. Using simple wetting models to describe the composite wetting of the cuticular surface structures results in underestimating the contact angles of water. Including the three-phase line tension allows for a prediction of contact angles in the observed range. The discrepancy between the contact angle predicted by simple models and those observed is especially large in the springtail Cryptopygus clavatus which changes, seasonally, from superhydrophobic to wetting without a large change in surface structure; C. clavatus does not have overhanging surface structures. This large change in observed contact angles can be explained with a modest change of the three-phase line tension.

A 3-D Numerical Modeling of Droplet Actuation via Electrowetting in Microchannels

2007 ◽  
Author(s):  
Alborz Arzpeyma ◽  
Ali Dolatabadi ◽  
Paula Wood-Adams
Keyword(s):  
Contact Angle ◽  
Numerical Modeling ◽  
Liquid Phase ◽  
Electric Field ◽  
Threshold Voltage ◽  
Contact Angle Hysteresis ◽  
Three Dimensions ◽  
Time Step ◽  
Droplet Behavior ◽  
Droplet Morphology

Numerical investigation is performed to study the droplet behavior under electrowetting actuation inside microchannels. Volume of Fluid (VOF) technique is employed to track the interface while the electric field is solved inside the whole domain in each time step simultaneously. The equations are solved in three dimensions for water as the liquid phase. Droplet morphology under the application of an electric field is investigated. Droplet velocity studied under different actuation voltages and compared to the experiments. Contact angle hysteresis and its effects on the threshold voltage are discussed.

Numerical simulation of EWOD on a printed circuit board for cleanroom-less digital fluidic manufacturing applications

2019 ◽  
Vol 38 (1) ◽  
pp. 119-137 ◽  
Author(s):  
Reza Hadjiaghaie Vafaie ◽  
Hossein Dehganpour ◽  
Abolfazl Moradpour
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Electric Field ◽  
Printed Circuit Board ◽  
Circuit Board ◽  
Angle Distribution ◽  
Content Type ◽  
Electrowetting On Dielectric ◽  
Printed Circuit ◽  
Wide Range

Purpose Digital microfluidic devices have been demonstrated to have great potential for a wide range of applications. These devices need expensive photolithography process and clean room facilities, while printed circuit board (PCB) technology provides high configurability and at low cost. This study aims to investigate the mechanism of electrowetting-on-a-dielectric (EWOD) on PCB by solving the multiphysics interaction between fluid droplet and electric field. The performance of system will be improved by inducing an efficient electric field inside the droplet. Design/methodology/approach To induce an electric field inside the droplet on a PCB and change the initial contact angle, the mechanism of EWOD is studied based on energy minimization method and a set of simulations are carried out by considering multiphysics interaction between the fluid droplet and external electric field. The performance of EWOD on a PCB system is investigated using different electrode structures. Findings Surface tension plays an efficient role in smaller sizes and can be used to move and control a fluid droplet on a surface by changing the interfacial surface tension. EWOD on a PCB system is studied. and it revealed that any change in electric field affects the droplet contact angle and as a result droplet deformation and movement. The electrode pattern is an important parameter which could change the electric potential distribution inside the droplet. Array of electrodes with square, zigzag interdigitated and crescent shapes are studied to enhance the EWOD force on a PCB substrate. Based on the results, the radial shape of the crescent electrodes keeps almost the same actuated contact line, applies uniform force on the droplet periphery and prevents the droplet from large deformation. A droplet velocity of 0.6 mm/s is achieved by exciting the crescent electrodes at 315 V. Furthermore, the behavior of system is characterized for process parameters such as actuation voltage, dielectric constant of insulator layer, fluidic material properties and the resultant velocity and contact angle. The study of contact angle distribution and droplet motion revealed that it is helpful to generate EWOD mechanism on a PCB which does not need more complicated fabrication processes. Originality/value The ability to handle and manipulate the droplets is very important for chemistry on-chip analysis such as immunoassay chips. Furthermore, a PCB-based electrowetting-on-dielectric device is of high interest because it does not need cleanroom facilities and avoids additional high-cost fabrication processes. In the present research, the EWOD mechanism is studied on a PCB by using different electrode patterns.

The Pressure of the Superhydrophobic Surface under Droplet Gravity

2012 ◽  
Vol 452-453 ◽  
pp. 91-94
Author(s):  
De Zhi Hu ◽  
Bin Zhou Mi ◽  
Xiao Chun Zhang ◽  
Bing Jun Kou
Keyword(s):  
Contact Angle ◽  
Hydrostatic Pressure ◽  
Gravity Model ◽  
Laplace Equation ◽  
Superhydrophobic Surface ◽  
Droplet Volume ◽  
Droplet Morphology ◽  
Wetting Process ◽  
Solid Liquid Interface ◽  
Solid Liquid

The paper started from the most basic physical law ‘Yang-Laplace equation’, combined with the invariably characteristics of the droplet volume in the Wetting process, established a novel Gravity Model. By numerical simulated, we found that the different of the internal hydrostatic pressure of droplet affected the droplet morphology directly. Otherwise, the paper studied importantly that the droplet gravity generated the pressure on the solid-liquid interface. When the contact angle is more than 172°, the droplet is non-stability in the Cassie states. Only the droplet can keep stability in the Wenzel states.

scholarly journals The Effect of Patterned Micro-Structure on the Apparent Contact Angle and Three-Dimensional Contact Line

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 92
Author(s):  
Patrick Foltyn ◽  
Ferdinand Restle ◽  
Markus Wissmann ◽  
Stefan Hengsbach ◽  
Bernhard Weigand
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Quality Standard ◽  
Apparent Contact Angle ◽  
Angle Distribution ◽  
Phase Contact ◽  
Angle Variation ◽  
Structured Surfaces ◽  
Three Phase ◽  
Direct Laser

The measurement of the apparent contact angle on structured surfaces is much more difficult to obtain than on smooth surfaces because the pinning of liquid to the roughness has a tremendous influence on the three phase contact line. The results presented here clearly show an apparent contact angle variation along the three phase contact line. Accordingly, not only one value for the apparent contact angle can be provided, but a contact angle distribution or an interval has to be given to characterize the wetting behavior. For measuring the apparent contact angle distribution on regularly structured surfaces, namely micrometric pillars and grooves, an experimental approach is presented and the results are provided. A short introduction into the manufacturing process of such structured surfaces, which is a combination of Direct LASER Writing (DLW) lithography, electroforming and hot embossing shows the high quality standard of the used surfaces.

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