Surface tension driven droplet transport in an open surface is increasingly becoming popular for various microfluidic applications. In this work, efficient transport of a glycerin droplet on an open wettability gradient surface with controlled wettability and confinement is numerically investigated. Nondimensional track width * (ratio of the width of the wettability gradient track and the initial droplet diameter d0) of a wettability gradient track laid on a superhydrophobic background represents wettability confinement. A lower value of * represents higher wettability confinement. Droplet behavior changes for different wettability confinements and gradients of the track. It is found that droplet velocity is a function of the wettability confinement and the gradient; droplet transport velocity is maximum for * = 0.8. Higher confinement (* < 0.8) leads to a significant reduction in droplet velocity. Droplet transport characteristics on hydrophilic–superhydrophilic, hydrophobic–superhydrophilic, and superhydrophobic–superhydrophilic tracks are studied. It is found that for a fixed length of the track, droplet velocity is maximum for the superhydrophobic–superhydrophilic track. A droplet transport regime is demonstrated for a wettability gradient track with different confinements, and it is found that the droplet is transported for wettability confinement * > 0.6 irrespective of the wettability gradient of the track. These findings provide valuable insight into efficient droplet manipulation in microfluidic devices.
REFERENCES
1.
X.
Yao
, Y.
Song
, and L.
Jiang
, “Applications of bio-inspired special wettable surfaces
,” Adv. Mater.
23
(6
), 719
–734
(2011
).2.
J.
Li
and Z.
Guo
, “Spontaneous directional transportations of water droplets on surfaces driven by gradient structures
,” Nanoscale
10
(29
), 13814
–13831
(2018
).3.
A.
Ghosh
, R.
Ganguly
, T. M.
Schutzius
, and C. M.
Megaridis
, “Wettability patterning for high-rate, pumpless fluid transport on open, non-planar microfluidic platforms
,” Lab Chip
14
(9
), 1538
–1550
(2014
).4.
A. A.
Darhuber
, J. P.
Valentino
, S. M.
Troian
, and S.
Wagner
, “Thermocapillary actuation of droplets on chemically patterned surfaces by programmable microheater arrays
,” J. Microelectromech. Syst.
12
(6
), 873
–879
(2003
).5.
S.
Mettu
and M. K.
Chaudhury
, “Motion of drops on a surface induced by thermal gradient and vibration
,” Langmuir
24
(19
), 10833
–10837
(2008
).6.
M.
Foroutan
, S. M.
Fatemi
, F.
Esmaeilian
, V.
Fadaei Naeini
, and M.
Baniassadi
, “Contact angle hysteresis and motion behaviors of a water nano-droplet on suspended graphene under temperature gradient
,” Phys. Fluids
30
(5
), 052101
(2018
).7.
V.
Jaiswal
, A.
Harikrishnan
, G.
Khurana
, and P.
Dhar
, “Ionic solubility and solutal advection governed augmented evaporation kinetics of salt solution pendant droplets
,” Phys. Fluids
30
(1
), 012113
(2018
).8.
S. K.
Cho
, H.
Moon
, and C.-J.
Kim
, “Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits
,” J. Microelectromech. Syst.
12
(1
), 70
–80
(2003
).9.
L.
Latorre
, J.
Kim
, J.
Lee
, P.-P.
De Guzman
, H. J.
Lee
, P.
Nouet
, and C.-J.
Kim
, “Electrostatic actuation of microscale liquid-metal droplets
,” J. Microelectromech. Syst.
11
(4
), 302
–308
(2002
).10.
G.
Kunti
, P. K.
Mondal
, A.
Bhattacharya
, and S.
Chakraborty
, “Electrothermally modulated contact line dynamics of a binary fluid in a patterned fluidic environment
,” Phys. Fluids
30
(9
), 092005
(2018
).11.
G.
Kunti
, A.
Bhattacharya
, and S.
Chakraborty
, “Electrothermally actuated moving contact line dynamics over chemically patterned surfaces with resistive heaters
,” Phys. Fluids
30
(6
), 062004
(2018
).12.
Z.
Long
, A. M.
Shetty
, M. J.
Solomon
, and R. G.
Larson
, “Fundamentals of magnet-actuated droplet manipulation on an open hydrophobic surface
,” Lab Chip
9
(11
), 1567
–1575
(2009
).13.
K.
Ichimura
, S.-K.
Oh
, and M.
Nakagawa
, “Light-driven motion of liquids on a photoresponsive surface
,” Science
288
(5471
), 1624
–1626
(2000
).14.
Y.
Zheng
, J.
Cheng
, C.
Zhou
, H.
Xing
, X.
Wen
, P.
Pi
, and S.
Xu
, “Droplet motion on a shape gradient surface
,” Langmuir
33
(17
), 4172
–4177
(2017
).15.
J. M.
Morrissette
, P. S.
Mahapatra
, A.
Ghosh
, R.
Ganguly
, and C. M.
Megaridis
, “Rapid, self-driven liquid mixing on open-surface microfluidic platforms
,” Sci. Rep.
7
(1
), 1800
(2017
).16.
S.
Dhiman
, K.
Jayaprakash
, R.
Iqbal
, and A. K.
Sen
, “Self-transport and manipulation of aqueous droplets on oil-submerged diverging groove
,” Langmuir
34
(41
), 12359
–12368
(2018
).17.
R. J.
Petrie
, T.
Bailey
, C. B.
Gorman
, and J.
Genzer
, “Fast directed motion of fakir droplets
,” Langmuir
20
(23
), 9893
–9896
(2004
).18.
X.
Xu
and T.
Qian
, “Droplet motion in one-component fluids on solid substrates with wettability gradients
,” Phys. Rev. E
85
(5
), 051601
(2012
).19.
O.
Hegde
, S.
Chakraborty
, P.
Kabi
, and S.
Basu
, “Vapor mediated control of microscale flow in sessile droplets
,” Phys. Fluids
30
(12
), 122103
(2018
).20.
J.-T.
Yang
, J. C.
Chen
, K.-J.
Huang
, and J. A.
Yeh
, “Droplet manipulation on a hydrophobic textured surface with roughened patterns
,” J. Microelectromech. Syst.
15
(3
), 697
–707
(2006
).21.
H. P.
Greenspan
, “On the motion of a small viscous droplet that wets a surface
,” J. Fluid Mech.
84
(1
), 125
–143
(1978
).22.
F.
Brochard
, “Motions of droplets on solid surfaces induced by chemical or thermal gradients
,” Langmuir
5
(2
), 432
–438
(1989
).23.
R. S.
Subramanian
, N.
Moumen
, and J. B.
McLaughlin
, “Motion of a drop on a solid surface due to a wettability gradient
,” Langmuir
21
(25
), 11844
–11849
(2005
).24.
M. K.
Chaudhury
and G. M.
Whitesides
, “How to make water run uphill
,” Science
256
(5063
), 1539
–1541
(1992
).25.
N.
Moumen
, R. S.
Subramanian
, and J. B.
McLaughlin
, “Experiments on the motion of drops on a horizontal solid surface due to a wettability gradient
,” Langmuir
22
(6
), 2682
–2690
(2006
).26.
M. K.
Chaudhury
, A.
Chakrabarti
, and S.
Daniel
, “Generation of motion of drops with interfacial contact
,” Langmuir
31
(34
), 9266
–9281
(2015
).27.
O.
Bliznyuk
, H. P.
Jansen
, E. S.
Kooij
, H. J.
Zandvliet
, and B.
Poelsema
, “Smart design of stripe-patterned gradient surfaces to control droplet motion
,” Langmuir
27
(17
), 11238
–11245
(2011
).28.
Y.
Ito
, M.
Heydari
, A.
Hashimoto
, T.
Konno
, A.
Hirasawa
, S.
Hori
, K.
Kurita
, and A.
Nakajima
, “The movement of a water droplet on a gradient surface prepared by photodegradation
,” Langmuir
23
(4
), 1845
–1850
(2007
).29.
C.
Liu
, J.
Sun
, J.
Li
, C.
Xiang
, L.
Che
, Z.
Wang
, and X.
Zhou
, “Long-range spontaneous droplet self-propulsion on wettability gradient surfaces
,” Sci. Rep.
7
(1
), 7552
(2017
).30.
Q.
Liu
and B.
Xu
, “A unified mechanics model of wettability gradient-driven motion of water droplet on solid surfaces
,” Extreme Mech. Lett.
9
, 304
–309
(2016
).31.
K. A.
Raman
, “Dynamics of simultaneously impinging drops on a dry surface: Role of inhomogeneous wettability and impact shape
,” J. Colloid Interface Sci.
516
, 232
–247
(2018
).32.
J.-J.
Huang
, H.
Huang
, and X.
Wang
, “Numerical study of drop motion on a surface with stepwise wettability gradient and contact angle hysteresis
,” Phys. Fluids
26
(6
), 062101
(2014
).33.
M.
Ahmadlouydarab
and J. J.
Feng
, “Motion and coalescence of sessile drops driven by substrate wetting gradient and external flow
,” J. Fluid Mech.
746
, 214
–235
(2014
).34.
J.
Huang
, C.
Shu
, and Y.
Chew
, “Numerical investigation of transporting droplets by spatiotemporally controlling substrate wettability
,” J. Colloid Interface Sci.
328
(1
), 124
–133
(2008
).35.
M.
Sussman
, P.
Smereka
, and S.
Osher
, “A level set approach for computing solutions to incompressible two-phase flow
,” J. Comput. Phys.
114
(1
), 146
–159
(1994
).36.
Y.
Dai
, Z.
Zhou
, J.
Lin
, and J.
Han
, “Modeling of two-phase flow in rough-walled fracture using level set method
,” Geofluids
2017
, 2429796
.37.
H.
Grzybowski
and R.
Mosdorf
, “Modelling of two-phase flow in a minichannel using level-set method
,” J. Phys.: Conf. Ser.
530
, 012049
(2014
).38.
C. Multiphysics, Comsol multiphysics CFD module user guide (version 5.3 a), COMSOL,
2015
, 208
–265
.39.
H.
Matsui
, Y.
Noda
, and T.
Hasegawa
, “Hybrid energy-minimization simulation of equilibrium droplet shapes on hydrophilic/hydrophobic patterned surfaces
,” Langmuir
28
(44
), 15450
–15453
(2012
).© 2019 Author(s).
2019
Author(s)
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