Passive sorting of emulsion droplets with different interfacial properties using laser-patterned surfaces

  • Zeeshan Rashid
  • Ahmet Erten
  • Berna Morova
  • Metin Muradoglu
  • Alexandr Jonáš
  • Alper KirazEmail author
Research Paper


We demonstrate passive sorting of emulsion microdroplets based on differences in their interfacial tension and contact angle. The sorted droplets are flowing inside a microfluidic channel featuring a shallow guiding track (depth \(\sim 0.6\,\upmu {\text {m}}\)) defined by femtosecond laser micromachining in polydimethylsiloxane coating deposited on glass. Under these flow conditions, the droplets experience a confinement force that pulls them into the track; this force depends on the interfacial tension and the difference between the contact angles inside and outside the ablated track. The interplay between the confinement force, fluid drag, and wall friction then determines the trajectory of the droplet along the guiding track. We investigate experimentally the droplet trajectory as a function of droplet velocity and angle between the track and the channel axis and demonstrate precise control of droplet direction by adjusting the track angle. Moreover, we show that droplets of liquids with different interfacial tensions and contact angles travel different distances along the guiding track at a constant flow rate, which can be used for droplet sorting. We develop a theoretical model that incorporates the droplet position with respect to the ablated track, interfacial tension, and contact angles to predict the droplet trajectory under given experimental conditions. Thus, the dynamic behavior of the droplets leading to different guiding scenarios can be studied without the need of computationally expensive fluid dynamics simulations. The presented study paves the way for designing and optimizing new systems for advanced manipulation of droplets of different content using potentially reconfigurable guiding tracks.



This work was supported by TÜBİTAK (Grants nos. 112T972 and 117F348) and HEC Pakistan (Ph.D. scholarship of Z.R.). We also thank KUYTAM (Koç University Surface Science and Technology Center) for laser ablation experiments and characterization measurements.

Supplementary material

10404_2019_2236_MOESM1_ESM.mp4 (17.1 mb)
Supporting information available Experimental details, CA measurements, surface topography measurements, further details on droplet geometrical parameters and on modeling of confinement force, together with experimental images and movies. (MP4 17533KB)
10404_2019_2236_MOESM2_ESM.pdf (2.4 mb)
Supplementary Material 2 (PDF 2487KB)


  1. Abate AR, Agresti JJ, Weitz DA (2010) Microfluidic sorting with high-speed single-layer membrane valves. Appl Phys Lett 96:203509CrossRefGoogle Scholar
  2. Ahn K, Kerbage C (2005) Dielectrophoretic manipulation of drops for high-speed microfluidic sorting devices. Appl Phys Lett 88:24104CrossRefGoogle Scholar
  3. Bain RM, Sathyamoorthi S, Zare RN (2017) On-droplet chemistry: the cycloaddition of diethyl azodicarboxylate and quadricyclane. Angew Chem Int Edn 56:15083–15087CrossRefGoogle Scholar
  4. Baret JC, Miller OJ, Taly V, Ryckelynck M, Harrak AE, Frenz L, Rick C, Samuels ML, Hutchison JB, Agresti JJ, Link DR, Weitz DA, Griffiths AD (2009) Fluorescence-activated droplet sorting: efficient microfluidic cell sorting based on enzymatic activity. Lab Chip 9:1850–1858CrossRefGoogle Scholar
  5. Beatus T, Bar-Ziv RH, Tlusty T (2012) The physics of 2D microfluidic droplet ensembles. Phys Rep 516:103–145CrossRefGoogle Scholar
  6. Brouzes E, Kruse T, Kimmerling R, Strey HH (2015) Rapid and continuous magnetic separation in droplet microfluidic devices. Lab Chip 15:908–919CrossRefGoogle Scholar
  7. Butt H-J, Gao N, Papadopoulos P, Steffen W, Kappl M, Berger R (2017) Energy dissipation of moving drops on superhydrophobic and superoleophobic surfaces. Langmuir 33:107–116CrossRefGoogle Scholar
  8. Chen Y, Tian Y, Xu Z, Wang X, Yu S, Dong L (2016) Microfluidic droplet sorting using integrated bilayer micro-valves. Appl Phys Lett 109:143510CrossRefGoogle Scholar
  9. Dangla R, Lee S, Baroud CN (2011) Trapping microfluidic drops in wells of surface energy. Phys Rev Lett 107:12450CrossRefGoogle Scholar
  10. de Saint Vincent MR, Wunenburger R, Delville JP (2008) Laser switching and sorting for high speed digital microfluidics. Appl Phys Lett 92:154105CrossRefGoogle Scholar
  11. Eckmann D, Cavanagh D, Branger A (2001) Wetting characteristics of aqueous surfactant-laden drops. J Colloid Interface Sci 242:386–394CrossRefGoogle Scholar
  12. Fradet E, McDougall C, Abbyad P, Dangla R, McGloin D, Baroud CN (2011) Combining rails and anchors with laser forcing for selective manipulation within 2D droplet arrays. Lab Chip 11:4228–4234CrossRefGoogle Scholar
  13. Guo F, Ji XH, Kan Liu RXH, Zhao LB, Guo ZX, Liu W, Guo SS, Zhao XZ (2010) Droplet electric separator microfluidic device for cell sorting. Appl Phys Lett 96:193701CrossRefGoogle Scholar
  14. Hatch AC, Patel A, Beer NR, Lee AP (2013) Passive droplet sorting using viscoelastic flow focusing. Lab Chip 13:1308–1315CrossRefGoogle Scholar
  15. Kamalakshakurup G, Basu AS (2013) Size based droplet sorting with wide tuning range using tensiophoresisGoogle Scholar
  16. Khodaparast S, Atasi O, Deblais A, Scheid B, Stone HA (2017) Dewetting of thin liquid films surrounding air bubbles in microchannels. Langmuir 34:71–99Google Scholar
  17. Lim HS, Han JT, Kwak D, Jin M, Cho K (2006) Photoreversibly switchable superhydrophobic surface with erasable and rewritable pattern. J Am Chem Soc 128:14458–14459CrossRefGoogle Scholar
  18. Mannetje D, Ghosh S, Lagraauw R, Otten S, Pit A, Berendsen C, Zeegers J, van den Ende D, Mugele F (2014) Trapping of drops by wetting defects. Nature Comm 5:1–7CrossRefGoogle Scholar
  19. Muradoglu M, Stone HA (2007) Motion of large bubbles in curved channels. J Fluid Mech 570:455–466CrossRefGoogle Scholar
  20. Olin P, Lindstrom SB, Pettersson T, Wagberg L (2013) Water drop friction on superhydrophobic surfaces. Langmuir 29:9079–9089CrossRefGoogle Scholar
  21. Pit AM, Bonestroo S, Wijnperle D, Duits MHG, Mugele F (2016) Electrode-assisted trapping and release of droplets on hydrophilic patches in a hydrophobic microchannel. Microfluid Nanofluid 20:1–12CrossRefGoogle Scholar
  22. Quere D (2008) Wetting and roughness. Annu Rev Mater Res 38:71–99CrossRefGoogle Scholar
  23. Rashid Z, Morova B, Yaman O, Soydan S, Birer O, Yilgor I, Kiraz A (2018) Reconfigurable and permanent wetting patterns on polymer surfaces obtained using plasma oxidation and laser ablation. Opt Data Process Storage 4:22–29CrossRefGoogle Scholar
  24. Rashid Z, Coskun UC, Morova Y, Morova B, Bozkurt AA, Erten A, Jonas A, Akturk S, Kiraz A (2017) Guiding of emulsion droplets in microfluidic chips along shallow tracks defined by laser ablation. Microfluid Nanofluid 21Google Scholar
  25. Sims CE, Allbritton NL (2007) Analysis of single mammalian cells on-chip. Lab Chip 7:423–440CrossRefGoogle Scholar
  26. Smith JD, Dhiman R, Anand S, Reza-Garduno E, Cohen RE, McKinley GH, Varanasi KK (2012) Droplet mobility on lubricant-impregnated surfaces. Soft Matter 9:1772–1780CrossRefGoogle Scholar
  27. Stone H (1994) Dynamics of drop deformation and breakup in viscous fluids. Annu Rev Fluid Mech 26:65–102MathSciNetCrossRefGoogle Scholar
  28. Tan YC, Fisher JS, Lee AI, Cristini V, Lee AP (2004) Design of microfluidic channel geometries for the control of droplet volume, chemical concentration, and sorting. Lab Chip 4:292–298CrossRefGoogle Scholar
  29. Tan YC, Ho YL, Lee AP (2007) Microfluidic sorting of droplets by size. Microfluid Nanofluid 4:343–348CrossRefGoogle Scholar
  30. Than P, Preziosi L, Josephl D, Arney M (1988) Measurement of interfacial tension between immiscible liquids with the spinning road tensiometer. J Colloid Interface Sci 124:552–559CrossRefGoogle Scholar
  31. Theberge AB, Courtois F, Schaerli Y, Fischlechner M, Abell C, Hollfelder F, Huck WTS (2010) Microdroplets in microfluidics: an evolving platform for discoveries in chemistry and biology. Angew Chem Int Edn 49:5846–5868CrossRefGoogle Scholar
  32. Xi HD, Zheng H, Guo W, Calvo AMG, Ai Y, Tsao CW, Zhou J, Li W, Huang Y, Nguyen N-T, Tan SH (2017) Active droplet sorting in microfluidics: a review. Lab Chip 17:751–771CrossRefGoogle Scholar
  33. Yan X, Bain R, Cooks RG (2016) Organic reactions in microdroplets: reaction acceleration revealed by mass spectrometry. Angew Chem Int Edn 55:12960–12972CrossRefGoogle Scholar
  34. Yoon DH, Numakunai S, Nakahara A, Sekiguchi T, Shoji S (2014) Hydrodynamic on-rail droplet pass filter for fully passive sorting of droplet-phase samples. RSC Adv 4:37721–37725CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Electrical and Electronics EngineeringKoç UniversityIstanbulTurkey
  2. 2.Department of Electronics and Communication EngineeringIstanbul Technical UniversityIstanbulTurkey
  3. 3.Department of PhysicsKoç UniversityIstanbulTurkey
  4. 4.Department of Mechanical EngineeringKoç UniversityIstanbulTurkey
  5. 5.The Czech Academy of Sciences, Institute of Scientific InstrumentsBrnoCzech Republic

Personalised recommendations