Modeling and simulation of droplet translocation and fission by electrowetting-on-dielectrics (EWOD)

Abstract

This paper discusses methods of microfluidic droplet actuation by means of electrowetting-on-dielectrics (EWOD) and provides a technique for modeling and simulating a microfluidic device by using the computational fluid dynamics (CFD) program, Flow3D. Digital or droplet microfluidics implies the manipulation of droplets on a scale of nanoliters (10^-9 L) to femtoliters (10^-15 L), as opposed to continuous microfluidics that involve the control of continuous fluid within a channel. The two operations in focus here are droplet translocation (moving) and droplet fission (splitting), in which the pressures and velocities within the droplet are analyzed and compared to existing works, both theoretical and experimental. The variation in the pressure of the leading and trailing faces of a droplet indicates the variation in surface energy—an important parameter that explains how a droplet will move toward a region of higher electric potential. The higher voltage on one side of a droplet reduces surface energy, which leads to an induced pressure drop, thus resulting in fluid motion. Flow3D simulations are for both water and blood droplets at voltages between 50 V and 200 V, and the droplet size, surface properties (Teflon coated), and geometry of the system are kept constant for each operation. Some peculiarities of the simulation are brought to light, such as instabilities of the system to higher voltages and fluids with higher dielectric constants, as well as the creation of a tertiary droplet when the applied voltage causes a large enough force during fission. The force distribution across the droplet provides a general understanding of the electrowetting effect and more specifically allows for a comparison between the effects that different voltages have on the forces at the droplet surface. The droplet position and mean kinetic energy of the droplet are also investigated and compared to other works, proving the dynamics of a droplet motion found here.

Key words： electrowetting-on-dielectrics (EWOD); electrowetting; microfluidics; droplet translocation; droplet fission; Flow3D; dielectric constant

References

1 Teh S Y, Lin R, Hung L H, Lee A P. Droplet microfluidics. Lab on a Chip, 2008, 8(2): 198–220

2 Mugele F, Baret J. Electrowetting: from basics to applications. Journal of Physics: Condensed Matter, 2005, 17(28): R705–R774

3 Abdelgawad M, Wheeler A R. The digital revolution: a new paradigm for micro fluidics. Advanced Materials, 2009, 21(8): 920–925

4 Zeng J. Modeling and simulation of electrified droplets and its application to computer-aided design of digital microfluidics. IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2006, 25(2): 224–233

5 Zeng J, Korsmeyer T. Principles of droplet electrohydrodynamics for lab-on-a-chip. Lab on a Chip, 2004, 4(4): 265–277

6 Young P M, Mohseni K. Calculation of DEP and EWOD Forces for application in digital microfluidics. Journal of Fluids Engineering, 2008, 130(8): 1603–1612

7 Herberth U. Fluid manipulation by means of electrowetting-on-dielectric. Dissertation for the Doctoral Degree<DissertationTip/>, Freiburg: Albert Ludwig University, 2006

8 de Lazzer A, Dreyer M, Rath H J. Particle-surface capillary forces. Lamgmuir, 1999, 15(13): 4551–4559

9 Deng X, Luo R, Chen H, Liu B, Feng Y, Sun Y. Synthesis and surface properties of PDMS-acrylate emulsion with gemini surfactant as co-emulsifier. Colloid & Polymer Science, 2007, 285(8): 923–930

10 Baird E, Young P, Mohseni K. Electrostatic force calculation for an EWOD-actuated droplet. Microfluidics and Nanofluidics, 2007, 3(6): 635–644

11 Kuo J S, Spicar-Mihalic P, Rodriguez I, Chiu D T. Electrowetting-induced droplet movement in an immiscible medium. Langmuir, 2003, 19(2): 250–255

12 Schrauth A J, Saka N, Suh N P. Development of nano-structured hemocompatible surfaces. MIT—Park Center for Complex Systems, 2004,

13 Dolatabadi A, Mohseni K, Arzpeyma A. Behaviour of a moving droplet under electrowetting actuation: numerical simulation. Canadian Journal of Chemical Engineering, 2006, 84(1): 17–21

14 Lin J L, Lee G B, Chang Y H, Lien K Y. Model description of contact angles in electrowetting on dielectric layers. Langmuir, 2006, 22(1): 484–489

15 Shikhmurzaev Y D. Singularities at the moving contact line. mathematical, physical and computational aspects. Physica D: Nonlinear Phenomena, 2006, 217(2): 121–133

16 Su F, Chakrabarty K, Fair R B. Microfluidics-based biochips: technology issues, implementation platforms, and design-automation challenges. IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2006, 25(2): 211–223

17 Fair R B, Khlystov A, Tailor T D, Ivanov V, Evans R D, Srinivasan V, Pamula V K, Pollack M G, Griffin P B, Zhou J. Chemical and biological applications of digital-microfluidic devices. IEEE Design & Test of Computers, 2007, 24(1): 10–24

18 Cheow L F, Yobas L, Kwong D L. Digital microfluidics: droplet based logic gates. Applied Physics Letters, 2007, 90(5): 054107

19 Cho S K, Moon H, Kim C J. Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits. Journal of Microelectromechanical Systems, 2003, 12(1): 70–80

20 Lienemann J, Greiner A, Korvink J G. Modeling, simulation, and optimization of electrowetting. IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2006, 25(2): 234–247

21 Su F, Zeng J. Computer-aided design and test for digital micro fluidics. IEEE Design & Test of Computers, 2007, 24(1): 60–70

22 Jang L S, Lin G H, Lin Y L, Hsu C Y, Kan W H, Chen C H. Simulation and experimentation of a microfluidic device based on electrowetting on dielectric. Biomedical Microdevices, 2007, 9(6): 777–786

23 Walker S W, Shapiro B. Modeling the fluid dynamics of electrowetting on dielectric (EWOD). Journal of Microelectromechanical Systems, 2006, 15(4): 986–1000

24 Glatzel T, Litterst C, Cupelli C, Lindemann T, Moosman C, Niekrawietz R, Streule W, Zengerle R, Koltay P. Computational fluid dynamics (CFD) software tools for microfluidic applications— a case study. Computers & Fluids, 2008, 37(3): 218–235

25 Fawehinmi O B, Gaskell P H, Jimack P K, Kapur N, Thompson H M. A combined experimental and computational fluid dynamics analysis of the dynamics of drop formation. In: Proceedings of the Institution of Mechanical Engineers. Part C, Journal of Mechanical Engineering Science, 2005, 219(9): 933–947

26 Bahadur V, Garimella S V. An energy-based model for electrowetting-induced droplet actuation. Journal of Micromechanics and Microengineering, 2006, 16(8): 1494–1503

27 Kumari N, Bahadur V, Garimella S V. Electrical actuation of dielectric droplets. Journal of Micromechanics and Microengineering, 2008, 18(8): 085018

28 Arzpeyma A, Bahseen S, Dolatabadi A, Woodadams P. A coupled electro-hydrodynamic numerical modelling of droplet actuation by electrowetting. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008, 323(1–3): 28–35

29 Le Berre M, Chen Y, Crozatier C, Zhang Z L. Electrocapillary force actuation of microfluidic elements. Microelectronic Engineering, 2005, 78–79: 93–99

30 Pollack M G, Fair R B, Shenderov A D. Electrowetting-based actuation of liquid droplets for microfluidic applications. Applied Physics Letters, 2000, 77(11): 1725–1726

31 Pollack M G, Shenderov A D, Fair R B. Electrowetting-based actuation of droplets for integrated microfluidics. Lab on a Chip, 2002, 2(2): 96–101

32 Wilson M C T, Summers J L, Shikhmurzaev Y D, Clarke A, Blake T D. Nonlocal hydrodynamic influence on the dynamic contact angle: slip models versus experiment. Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, 2006, 73(4): 041606–041616