The spreading dynamics of a drop deposited on a superhydrophilic micropillar array are qualitatively different from those on a smooth surface in that a thin fringe layer rapidly wicks into microstructures while the bulk collapses in the center. Here we experimentally measure the temporal evolution of the shapes of water and silicone oil drops on the superhydrophilic surfaces, and find various power laws that describe the spreading dynamics. The bulk radius increases initially but shrinks in the late stages for drainage of its volume by wicking. The fringe film tends to grow diffusively for the entire timespan of spreading with the effective diffusivity being a function of surface tension, pillar height, viscosity, and surface roughness. The entire footprint is shown to grow like t1/4, t being time, for the entire time range, which allows us to estimate the time for complete drop spreading.
REFERENCES
1.
D.
Richard
, C.
Clanet
, and D.
Quéré
, “Contact time of a bouncing drop
,” Nature
417
, 811
(2002
).2.
C.
Clanet
, C.
Béguin
, D.
Richard
, and D.
Quéré
, “Maximal deformation of an impacting drop
,” J. Fluid Mech.
517
, 199
–208
(2004
).3.
Z.
Wang
, C.
Lopez
, A.
Hirsa
, and N.
Koratkar
, “Impact dynamics and rebound of water droplets on superhydrophobic carbon nanotube arrays
,” Appl. Phys. Lett.
91
, 023105
(2007
).4.
P.
Tsai
, S.
Pacheco
, C.
Pirat
, L.
Lefferts
, and D.
Lohse
, “Drop impact upon micro- and nanostructured superhydrophobic surfaces
,” Langmuir
25
, 12293
–12298
(2009
).5.
L.
Courbin
, E.
Denieul
, E.
Dressaire
, M.
Roper
, A.
Ajdari
, and H. A.
Stone
, “Imbibition by polygonal spreading on microdecorated surfaces
,” Nature Mater.
6
, 661
–664
(2007
).6.
S. J.
Kim
, M.-W.
Moon
, K.-R.
Lee
, D.-Y.
Lee
, Y. S.
Chang
, and H.-Y.
Kim
, “Liquid spreading on superhydrophilic micropillar arrays
,” J. Fluid Mech.
680
, 477
–487
(2011
).7.
F.
Brochard-Wyart
, H.
Hervet
, C.
Redon
, and F.
Rondelez
, “Spreading of “heavy” droplets. I. Theory
,” J. Colloid Interface Sci.
142
, 518
(1991
).8.
G.
McHale
, N. J.
Shirtcliffe
, S.
Aqil
, C. C.
Perry
, and M. I.
Newton
, “Topography driven spreading
,” Phys. Rev. Lett.
93
, 036102
(2004
).9.
A. W.
Martinez
, S. T.
Phillips
, and G. M.
Whitesides
, “Three-dimensional microfluidic devices fabricated in layered paper and tape
,” Proc. Natl. Acad. Sci. U.S.A.
105
, 19606
(2008
).10.
C.
Gans
, R.
Merlin
, and W. F. C.
Blumer
, “The water-collecting mechanism of Moloch horridus re-examined
,” Amphib.-Reptil.
3
, 57
(1982
).11.
W. C.
Sherbrooke
, Introduction to Horned Lizards of North America
(University of California Press
, Berkeley, CA
, 2003
).12.
P.
Comanns
, C.
Effertz
, F.
Hischen
, K.
Staudt
, W.
Böhme
, and W.
Baumgartner
, “Moisture harvesting and water transport through specialized micro-structures on the integument of lizards
,” Beilstein J. Nanotechnol.
2
, 204
(2011
).13.
A.
Lee
, M.-W.
Moon
, H.
Lim
, W.-D.
Kim
, and H.-Y.
Kim
, “Water harvest via dewing
,” Langmuir
28
, 10183
(2012
).14.
J. W.
Yi
, M.-W.
Moon
, S. F.
Ahmed
, H.
Kim
, T.-G.
Cha
, H.-Y.
Kim
, S.-S.
Kim
, and K.-R.
Lee
, “Long-lasting hydrophilicity on nanostructured Si-incorporated diamond-like carbon films
,” Langmuir
26
, 17203
–17209
(2010
).15.
P.-G.
de Gennes
, F.
Brochard-Wyart
, and D.
Quéré
, Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves
(Springer
, New York
, 2004
).16.
F.
Brochard-Wyart
, G.
Debrégeas
, and P.-G.
de Gennes
, “Spreading of viscous droplets on a non viscous liquid
,” Colloid Polym. Sci.
274
, 70
–72
(1996
).17.
S. L.
Cormier
, J. D.
McGraw
, T.
Salez
, E.
Raphael
, and K.
Dalnoki-Veress
, “Beyond Tanner's law: Crossover between spreading regimes of a viscous droplet on an identical film
,” Phys. Rev. Lett.
109
, 154501
(2012
).18.
L. H.
Tanner
, “The spreading of silicone oil drops on horizontal surfaces
,” J. Phys. D
12
, 1473
–1484
(1979
).19.
S.
Schiaffino
and A. A.
Sonin
, “Molten drop deposition and solidification at low Weber numbers
,” Phys. Fluids
9
, 3172
–3187
(1997
).20.
G.
Guéna
, C.
Poulard
, and A. M.
Cazabat
, “The leading edge of evaporating droplets
,” J. Colloid Interface Sci.
312
, 164
–171
(2007
).21.
J.
Bico
, U.
Thiele
, and D.
Quéré
, “Wetting of textured surfaces
,” Colloids Surf.
206
, 41
–46
(2002
).22.
J.
Kim
, M.-W.
Moon
, K.-R.
Lee
, L.
Mahadevan
, and H.-Y.
Kim
, “Hydrodynamics of writing with ink
,” Phys. Rev. Lett.
107
, 264501
(2011
).23.
R.
Xiao
, R.
Enright
, and E. N.
Wang
, “Prediction and optimization of liquid propagation in micropillar arrays
,” Langmuir
26
, 15070
–15075
(2010
).24.
N.
Srivastava
, C.
Din
, A.
Judson
, N. C.
MacDonald
, and C. D.
Meinhart
, “A unified scaling model for flow through a lattice of microfabricated posts
,” Lab Chip
10
, 1148
–1152
(2010
).25.
M. L.
Blow
and J. M.
Yeomans
, “Anisotropic imbibition of surfaces patterned with polygonal posts
,” Philos. Trans. R. Soc. London, Ser. A
369
, 2519
–2527
(2011
).© 2013 AIP Publishing LLC.
2013
AIP Publishing LLC
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