The near-contact-line dynamics of evaporating sessile drops containing live E. coli cells is studied experimentally. The evaporation of the drop together with its pinned contact-line drives a radially outward fluid flow inside the drop concentrating the suspended cells near the contact-line. Our experiments reveal a collective behavior of the concentrated bacterial population near the contact-line appearing in the form of spatially periodic “bacterial jets” along the circumference of the drop. Based on a physical analysis of the continuum equations of bacterial suspensions, we hypothesize that the patterns result from a concentration instability driven by the active stress of swimming bacteria.
REFERENCES
1.
R. D.
Deegan
, O.
Bakajin
, T. F.
Dupont
, G.
Huber
, S. R.
Nagel
, and T. A.
Witten
, “Capillary flow as the cause of ring stains from dried liquid drops
,” Nature (London)
389
, 827
–829
(1997
).2.
R. D.
Deegan
, O.
Bakajin
, T. F.
Dupont
, G.
Huber
, S. R.
Nagel
, and T. A.
Witten
, “Contact line deposits in an evaporating drop
,” Phys. Rev. E
62
, 756
–765
(2000
).3.
H.
Hu
and R. G.
Larson
, “Analysis of the microfluid flow in an evaporating sessile droplet
,” Langmuir
21
, 3963
–3971
(2005
).4.
D. L.
Koch
and G.
Subramanian
, “Collective hydrodynamics of swimming microorganisms: Living fluids
,” Annu. Rev. Fluid Mech.
43
, 637
–659
(2011
).5.
X. L.
Wu
and A.
Libchaber
, “Particle diffusion in a quasi-two-dimensional bacterial bath
,” Phys. Rev. Lett.
84
, 3017
–3020
(2000
).6.
M. J.
Kim
and K. S.
Breuer
, “Enhanced diffusion due to motile bacteria
,” Phys. Fluids
16
, L78
–L81
(2004
).7.
I.
Tuval
, L.
Cisneros
, C.
Dombrowski
, C. W.
Wolgemuth
, J. O.
Kessler
, and R. E.
Goldstein
, “Bacterial swimming and oxygen transport near contact lines
,” Proc. Natl. Acad. Sci. U.S.A.
102
, 2277
–2282
(2005
).8.
A.
Sokolov
, R. E.
Goldstein
, F. I.
Feldchtein
, and I. S.
Aranson
, “Enhanced mixing and spatial instability in concentrated bacterial suspensions
,” Phys. Rev. E
80
, 031903
(2009
).9.
M. A.
Bees
, P.
Andresn
, E.
Mosekilde
, and M.
Givskov
, “The interaction of thin-film flow, bacterial swarming and cell differentiation in colonies of Serratia liquefaciens
,” J. Math. Biol.
40
, 27
–63
(2000
).10.
J.-F.
Joanny
and S.
Ramaswamy
, “A drop of active matter
,” J. Fluid Mech.
705
, 46
–57
(2012
).11.
S.
Hou
, E. A.
Burton
, K. A.
Simon
, D.
Blodgett
, Y.-Y.
Luk
, and D.
Ren
, “Inhibition of Escherichia coli biofilm formation by self-assembled monolayers of functional alkanethiols on gold
,” Appl. Environ. Microbiol.
73
, 4300
–4307
(2007
).12.
13.
E.
Lauga
and T. R.
Powers
, “The hydrodynamics of swimming microorganisms
,” Rep. Prog. Phys.
72
, 096601
(2009
).14.
J. P.
Hernandez-Ortiz
, C. G.
Stoltz
, and M. D.
Graham
, “Transport and collective dynamics in suspensions of confined swimming particles
,” Phys. Rev. Lett.
95
, 204501
(2005
).15.
D.
Saintillan
and M. J.
Shelley
, “Orientational order and instabilities in suspensions of self-locomoting rods
,” Phys. Rev. Lett.
99
, 058102
(2007
).16.
P. T.
Underhill
, J. P.
Hernandez-Ortiz
, and M. D.
Graham
, “Diffusion and spatial correlations in suspensions of swimming particles
,” Phys. Rev. Lett.
100
, 248101
(2008
).17.
N. H.
Mendelson
, A.
Bourque
, K.
Wilkening
, K. R.
Anderson
, and J. C.
Watkins
, “Organized cell swimming motions in Bacillus subtilis colonies: Patterns of short-lived whirls and jets
,” J. Bacteriol.
181
, 600
–609
(1999
).18.
C.
Dombrowski
, L.
Cisneros
, S.
Chatkaew
, R. E.
Goldstein
, and J. O.
Kessler
, “Self-concentration and large-scale coherence in bacterial dynamics
,” Phys. Rev. Lett.
93
, 098103
(2004
).19.
A.
Sokolov
, I. S.
Aranson
, J. O.
Kessler
, and R. E.
Goldstein
, “Concentration dependence of the collective dynamics of swimming bacteria
,” Phys. Rev. Lett.
98
, 158102
(2007
).20.
T.
Ishikawa
, N.
Yoshida
, H.
Ueno
, M.
Wiedeman
, Y.
Imai
, and T.
Yamaguchi
, “Energy transport in a concentrated suspension of bacteria
,” Phys. Rev. Lett.
107
, 028102
(2011
).21.
J.
Dunkel
, S.
Heidenreich
, K.
Drescher
, H. H.
Wensink
, M.
Bär
, and R. E.
Goldstein
, “Fluid dynamics of bacterial turbulence
,” Phys. Rev. Lett.
110
, 228102
(2013
).22.
G.
Subramanian
and D. L.
Koch
, “Critical bacterial concentration for the onset of collective swimming
,” J. Fluid Mech.
632
, 359
–400
(2009
).23.
R. A.
Simha
and S.
Ramaswamy
, “Hydrodynamic fluctuations and instabilities in ordered suspensions of self-propelled particles
,” Phys. Rev. Lett.
89
, 058101
(2002
).24.
D.
Saintillan
and M. J.
Shelley
, “Instabilities and pattern formation in active particle suspensions: Kinetic theory and continuum simulations
,” Phys. Rev. Lett.
100
, 178103
(2008
).25.
D.
Saintillan
and M. J.
Shelley
, “Instabilities, pattern formation, and mixing in active suspensions
,” Phys. Fluids
20
, 123304
(2008
).26.
C.
Hohenegger
and M. J.
Shelley
, “Stability of active suspensions
,” Phys. Rev. E
81
, 046311
(2010
).27.
B.
Ezhilan
, A. A.
Pahlavan
, and D.
Saintillan
, “Chaotic dynamics and oxygen transport in thin films of aerotactic bacteria
,” Phys. Fluids
24
, 091701
(2012
).28.
T. V.
Kasyap
and D. L.
Koch
, “Chemotaxis driven instability of a confined bacterial suspension
,” Phys. Rev. Lett.
108
, 038101
(2012
).29.
T. V.
Kasyap
and D. L.
Koch
, “Instability of an inhomogeneous bacterial suspension subjected to a chemo-attractant gradient
,” J. Fluid Mech.
741
, 619
–657
(2014
).30.
See supplementary material at http://dx.doi.org/10.1063/1.4901958 for details on the preparation of bacterial suspensions, movies of the contact-line region of evaporating sessile drops containing wild-type (supplementary movie 1), smooth-swimming (supplementary movie 2), and incessantly tumbling E. coli cells (supplementary movie 3), and the movie of the contact-line region of non-evaporating drop containing wildtype E. coli cells (supplementary movie 4).
31.
H.
Hu
and R. G.
Larson
, “Evaporation of a sessile droplet on a substrate
,” J. Phys. Chem. B
106
, 1334
–1344
(2002
).32.
A.
Be'er
and R. M.
Harshey
, “Collective motion of surfactant-producing bacteria imparts superdiffusivity to their upper surface
,” Biophys. J.
101
, 1017
–1024
(2011
).© 2014 AIP Publishing LLC.
2014
AIP Publishing LLC
You do not currently have access to this content.
