Research Papers: Heat and Mass Transfer

A Numerical Study on Electrowetting-Induced Droplet Detachment From Hydrophobic Surface

[+] Author and Article Information
Md Ashraful Islam

Department of Mechanical and
Aerospace Engineering,
University of Texas at Arlington,
Arlington, TX 76019
e-mail: mdashraful.islam@mavs.uta.edu

Albert Y. Tong

Department of Mechanical and
Aerospace Engineering,
University of Texas at Arlington,
Arlington, TX 76019
e-mail: tong@uta.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received November 15, 2016; final manuscript received October 1, 2017; published online February 21, 2018. Editor: Portonovo S. Ayyaswamy.

J. Heat Transfer 140(5), 052003 (Feb 21, 2018) (11 pages) Paper No: HT-16-1745; doi: 10.1115/1.4038540 History: Received November 15, 2016; Revised October 01, 2017

Electrowetting-induced microwater droplet detachment from hydrophobic surface has been studied numerically. The governing equations for transient microfluidic flow are solved by a finite volume scheme with a two-step projection method on a fixed computational domain. The free surface of the droplet is tracked by the volume-of-fluid method with the surface tension force determined by the continuum surface force (CSF) model. The static contact angle has been implemented using a wall-adhesion boundary condition at the solid–liquid interface, while the dynamic contact angle is computed assuming a fixed deflection from the static contact angle. The results of the numerical model have been validated with published experimental data and the physics of stretching, recoiling, and detachment of the droplet have been investigated. A parametric study has been performed in which the effects of droplet volume, voltage amplitude, and voltage pulse width have been examined.

Copyright © 2018 by ASME
Topics: Drops
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Enright, R. , Miljkovic, N. , Alvarado, J. L. , Kim, K. , and Rose, J. W. , 2014, “ Dropwise Condensation on Micro- and Nanostructured Surfaces,” Nanoscale Microscale Thermophys. Eng., 18(3), pp. 223–250. [CrossRef]
Mugele, F. , Baret, J.-C. , and Steinhauser, D. , 2006, “ Microfluidic Mixing Through Electrowetting-Induced Droplet Oscillations,” Appl. Phys. Lett., 88(20), p. 204106. [CrossRef]
Lee, S. J. , Lee, S. , and Kang, K. H. , 2012, “ Droplet Jumping by Electrowetting and Its Application to the Three-Dimensional Digital Microfluidics,” Appl. Phys. Lett., 100(8), p. 081604. [CrossRef]
Nelson, W. C. , and Kim, C. J. , 2012, “ Droplet Actuation by Electrowetting-on-Dielectrode (EWOD): A Review,” J. Adhes. Sci. Technol., 26(12–17), pp. 1747–1771.
Mugele, F. , and Baret, J.-C. , 2005, “ Electrowetting: From Basics to Applications,” J. Phys.: Condens. Matter, 17(28), pp. R705–R774. [CrossRef]
Cavalli, A. , Preston, D. J. , Tio, E. , Martin, D. W. , Miljkovic, N. , Wang, E. N. , Blanchette, F. , and Bush, J. W. M. , 2016, “ Electrically Induced Drop Detachment and Ejection,” Phys. Fluids, 28(2), p. 022101. [CrossRef]
Lee, S. J. , Hong, J. , Kang, K. H. , Kang, I. S. , and Lee, S. J. , 2014, “ Electrowetting-Induced Droplet Detachment From Hydrophobic Surfaces,” Langmuir, 30(7), pp. 1805–1811. [CrossRef] [PubMed]
Raman, K. A. , Jaiman, R. K. , Lee, T.-S. , and Low, H.-T. , 2016, “ A Numerical Study on Electrowetting-Induced Jumping and Transport of Droplet,” Int. J. Heat Mass Transfer, 99, pp. 805–821. [CrossRef]
Kershaw, D. S. , 1978, “ The Incomplete Cholesky-Conjugate Gradient Method for the Iterative Solution of Linear Equations,” J. Comput. Phys., 26(1), pp. 43–65. [CrossRef]
Hirt, C. W. , and Nichols, B. D. , 1981, “ Volume of Fluid (VOF) Method for the Dynamics of Free Boundaries,” J. Comput. Phys., 39(1), pp. 201–225. [CrossRef]
Youngs, D. L. , 1982, “ Time-Dependent Multi-Material Flow With Large Fluid Distortion,” Numerical Methods for Fluid Dynamics, Academic, New York, pp. 273–285.
Rudman, M. , 1997, “ Volume-Tracking Methods for Interfacial Flow Calculations,” Int. J. Numer. Methods Fluids, 24(7), pp. 671–691. [CrossRef]
Brackbill, J. U. , Kothe, D. B. , and Zemach, C. A. , 1992, “ Continuum Method for Modeling Surface Tension,” J. Comput. Phys., 100(2), pp. 335–354. [CrossRef]
Tong, A. Y. , and Wang, Z. , 2007, “ Relaxation Dynamics of a Free Elongated Liquid Ligament,” Phys. Fluids, 19(9), p. 092101. [CrossRef]
Islam, M. A. , 2016, “ Numerical Modeling of Capillary Driven Microfluidic Flow,” Ph.D. thesis, The University of Texas at Arlington, Arlington, TX.
Tong, A. Y. , and Wang, Z. , 2007, “ A Numerical Method for Capillarity-Dominant Free Surface Flows,” J. Comput. Phys., 221(2), pp. 506–523. [CrossRef]
Islam, M. A. , and Tong, A. Y. , 2017, “ A Numerical Study of Parallel-Plate and Open-Plate Droplet Transport in Electrowetting-on-Dielectrode (EWOD),” Numer. Heat Transfer, Part A, 71(8), pp. 805–821. [CrossRef]
Chow, T. S. , 1998, “ Wetting of Rough Surfaces,” J. Phys.: Condens. Matter, 10(27), pp. L445–L451. [CrossRef]
Kothe, D. B. , and Mjolsness, R. C. , 1992, “ RIPPLE: A New Model for Incompressible Flows With Free Surfaces,” AIAA J., 30(11), pp. 2694–2700. [CrossRef]
Senthilkumar, S. , Delaure, Y. M. C. , Murray, D. B. , and Donnelly, B. , 2011, “ The Effect of the VOF-CSF Static Contact Angle Boundary Condition on the Dynamics of Sliding and Bouncing Ellipsoidal Bubbles,” Int. J. Heat Fluid Flow, 32(5), pp. 964–972. [CrossRef]
Yin, G. , and Tong, A. Y. , 2015, “ A Numerical Study of Droplet Splitting and Merging in a Parallel-Plate Electrowetting-on-Dielectric Device,” ASME J. Heat Transfer, 137(9), p. 091016. [CrossRef]
Cho, S. K. , Moon, H. , and Kim, C.-J. , 2003, “ Creating, Transporting, Cutting and Merging Liquid Droplets by Electrowetting-Based Actuation for Digital Microfluidic Circuits,” J. Microelectromech. Syst., 12(1), pp. 70–80. [CrossRef]
Gupta, R. , Sheth, D. M. , Boone, T. K. , Sevilla, A. B. , and Frechette, J. , 2011, “ Impact of Pinning of the Triple Contact Line on Electrowetting Performance,” Langmuir, 27(24), pp. 14923–14929. [CrossRef] [PubMed]


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Fig. 1

Schematic of wall adhesion model and no-slip boundary condition

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Fig. 2

Schematic of experimental setup for electrowetting-induced droplet detachment [7]

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Fig. 3

Schematic of a DC square voltage pulse and corresponding contact angle

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Fig. 4

Numerical modeling of various static contact angles

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Fig. 5

Various stages of droplet detachment: (a) experimental [7] and (b) present numerical study

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Fig. 6

Base radius and apex height versus time during a 5 μL droplet detachment; numerical simulation at 135 V (left); experimental results [7] (right)

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Fig. 7

Pressure and velocity fields during droplet stretching

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Fig. 8

Energy analysis during recoiling and detachment

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Fig. 9

Pressure and velocity fields during droplet recoiling

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Fig. 10

Pressure and velocity fields during droplet detachment

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Fig. 11

Droplet spreading spectra for a 5 μL droplet for various actuating contact angles

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Fig. 12

Base radius at the instant of voltage release and maximum apex height versus pulse width (5 μL droplet with 116 deg/62 deg change in contact angle)

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Fig. 13

Pressure and velocity fields during droplet recoiling: (a) 4.6 ms pulse width (lower limit) and (b) 10.35 ms pulse width (upper limit)

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Fig. 14

Apex height and base radius versus time with 116 deg/62 deg change in contact angle. (Starting time shifted to the instant of voltage release.)

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Fig. 15

Droplet spreading spectrum for various droplet volumes: (a) without and (b) with normalization

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Fig. 16

Effect of actuating contact angle on the droplet detachment process for a 5 μL droplet

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Fig. 17

Apex height versus time for various droplet volumes

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Fig. 18

Threshold voltage for droplet detachment for various droplet volumes

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Fig. 19

Droplet detachment with various grid sizes




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