Effect of contact angle hysteresis on thermocapillary droplet actuation

Open microfluidic devices based on actuation techniques such as electrowetting, dielectrophoresis, or thermocapillary stresses require controlled motion of small liquid droplets on the surface of glass or silicon substrates. In this article we explore the physical mechanisms affecting thermocapillary migration of droplets generated by surface temperature gradients on the supporting substrate. Using a combination of experiment and modeling, we investigate the behavior of the threshold force required for droplet mobilization and the speed after depinning as a function of the droplet size, the applied thermal gradient and the liquid material parameters. The experimental results are well described by a hydrodynamic model based on earlier work by Ford and Nadim. The model describes the steady motion of a two-dimensional droplet driven by thermocapillary stresses including contact angle hysteresis. The results of this study highlight the critical role of chemical or mechanical hysteresis and the need to reduce this retentive force for minimizing power requirements in microfluidic devices. © 2005 American Institute of Physics . [DOI: 10.1063/1.1819979]

[1]  W. Deen.  Analysis Of Transport Phenomena , 1998 .

[2]  D. J. Harrison,et al.  Electroosmotic pumping and electrophoretic separations for miniaturized chemical analysis systems , 1994 .

[3]  John A. Rogers,et al.  Tunable optical fiber devices based on broadband long-period gratings and pumped microfluidics , 2003 .

[4]  M. Burns,et al.  Thermocapillary Pumping of Discrete Drops in Microfabricated Analysis Devices , 1999 .

[5]  W. A. Zisman,et al.  Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution , 1964 .

[6]  L. G. J. Fokkink,et al.  Fast Electrically Switchable Capillary Effects , 1998 .

[7]  B. J. Feenstra,et al.  Video-speed electronic paper based on electrowetting , 2003, Nature.

[8]  S. Troian,et al.  A study of mixing in thermocapillary flows on micropatterned surfaces , 2004, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[9]  Aa Anton Darhuber,et al.  Thermocapillary actuation of liquid flow on chemically patterned surfaces , 2003 .

[10]  A. Nadim,et al.  Thermocapillary migration of an attached drop on a solid surface , 1994 .

[11]  J. Israelachvili,et al.  Molecular mechanisms associated with adhesion and contact angle hysteresis of monolayer surfaces , 1991 .

[12]  Marya Lieberman,et al.  Growth of Ultrasmooth Octadecyltrichlorosilane Self-Assembled Monolayers on SiO2 , 2003 .

[13]  F. Brochard,et al.  Motions of droplets on solid surfaces induced by chemical or thermal gradients , 1989 .

[14]  Darrell H. Reneker,et al.  Motion of droplets along thin fibers with temperature gradient , 2002 .

[15]  C. Kim,et al.  Surface-tension-driven microactuation based on continuous electrowetting , 2000, Journal of Microelectromechanical Systems.

[16]  M. McGovern,et al.  Role of Solvent on the Silanization of Glass with Octadecyltrichlorosilane , 1994 .

[17]  Vargaftik,et al.  Handbook of Physical Properties of Liquids and Gases , 1983 .

[18]  R. H. Dettre,et al.  Contact Angle Hysteresis. IV. Contact Angle Measurements on Heterogeneous Surfaces1 , 1965 .

[19]  Daniel Y. Kwok,et al.  The effect of liquid properties to contact angle hysteresis , 2001 .

[20]  L. Tanner,et al.  The spreading of silicone oil drops on horizontal surfaces , 1979 .

[21]  N. Larsen,et al.  Effect of Solvents and Concentration on the Formation of a Self-Assembled Monolayer of Octadecylsiloxane on Silicon (001) , 2003 .

[22]  Joe T. Lin,et al.  Microfabricated Centrifugal Microfluidic Systems: Characterization and Multiple Enzymatic Assays , 1999 .

[23]  B. Dussan,et al.  On the nature of the dynamic contact angle: an experimental study , 1982, Journal of Fluid Mechanics.

[24]  Jens Anders Branebjerg,et al.  Microfluidics-a review , 1993 .

[25]  L. Scriven,et al.  Hydrodynamic Model of Steady Movement of a Solid / Liquid / Fluid Contact Line , 1971 .

[26]  A. Wolf,et al.  A Study of Alkyl Chain Conformational Changes in Self-Assembled n-Octadecyltrichlorosilane Monolayers on Fused Silica Surfaces , 2001 .

[27]  W. Rose,et al.  Moving interfaces and contact angle rate-dependency☆ , 1962 .

[28]  F. Rondelez,et al.  Evidence of a transition temperature for the optimum deposition of grafted monolayer coatings , 1992, Nature.

[29]  S. Wagner,et al.  Generation of high-resolution surface temperature distributions , 2002 .

[30]  J. Rabe,et al.  Effect of temperature on the dynamic contact angle , 1998 .

[31]  E. B. Dussan,et al.  LIQUIDS ON SOLID SURFACES: STATIC AND DYNAMIC CONTACT LINES , 1979 .

[32]  H. P. Greenspan,et al.  On the motion of a small viscous droplet that wets a surface , 1978, Journal of Fluid Mechanics.

[33]  Sigurd Wagner,et al.  Microfluidic actuation by modulation of surface stresses , 2003 .

[34]  Marc K. Smith.  Thermocapillary migration of a two-dimensional liquid droplet on a solid surface , 1995, Journal of Fluid Mechanics.

[35]  John A. Rogers,et al.  Dynamic tuning of optical waveguides with electrowetting pumps and recirculating fluid channels , 2002 .

[36]  R. Fair,et al.  Electrowetting-based actuation of liquid droplets for microfluidic applications , 2000 .

[37]  F. Rondelez,et al.  Silanization of Solid Substrates: A Step Toward Reproducibility , 1994 .

[38]  R. H. Dettre,et al.  Contact Angle Hysteresis: II. Contact Angle Measurements on Rough Surfaces , 1964 .

[39]  Stephen F. Bart,et al.  Microfabricated electrohydrodynamic pumps , 1990 .

[40]  Extrand,et al.  An Experimental Study of Contact Angle Hysteresis , 1997, Journal of colloid and interface science.

[41]  R. H. Dettre,et al.  Contact Angle Hysteresis: I. Study of an Idealized Rough Surface , 1964 .

[42]  T. Jones,et al.  Dielectrophoretic liquid actuation and nanodroplet formation , 2001 .

[43]  P. Gennes.  Wetting: statics and dynamics , 1985 .

[44]  Sigurd Wagner,et al.  Thermocapillary actuation of droplets on chemically patterned surfaces by programmable microheater arrays , 2003 .

[45]  Jaesung Jang,et al.  Theoretical and experimental study of MHD (magnetohydrodynamic) micropump , 2000 .

[46]  R. H. Dettre,et al.  Contact Angle Hysteresis. III. Study of an Idealized Heterogeneous Surface , 1964 .

[47]  A. Adamson.  Physical chemistry of surfaces , 1960 .

[48]  Françoise Brochard-Wyart,et al.  Motions of droplets on hydrophobic model surfaces induced by thermal gradients , 1993 .