V08 Droplets Lecture Notes WS 23 PDF

V8 V08 Droplets / Plugs in Micro Channels Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 1 Contents V8 Contents Droplets / Plugs in Micro Channels 8.1 Introduction 8.2 Properties 8.3 Formation of Dropl...

V8 V08 Droplets / Plugs in Micro Channels Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 1 Contents V8 Contents Droplets / Plugs in Micro Channels 8.1 Introduction 8.2 Properties 8.3 Formation of Droplets / Plugs 8.3.1 Capillary Number Ca 8.3.2 T-junction 8.3.3 Flow Focusing 8.3.4 Coaxial Injection 8.3.5 Inclined Cover Plate 8.4 Pressure in Micro Channels with Plugs Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 2 Learning Targets V8 Learning Targets  Formation of droplets / plugs  Capillary number  Laplace pressure in droplets Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 3 V8 8.1 Introduction Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 4 8.1 Introduction V8 5 Definition of Terms Plug / Slug Dispersed phase Continuous phase Capillary / microchannel wall Droplet Terms are not used consistently ! Droplets / Plugs / Slugs represents always the dispersed phase ! Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.1 Introduction V8  Droplet-based microfluidics  Plug-based microfluidics  Slug flow microfluidics  Segmented-flow microfluidics  Multiphase microfluidics …is the science and technology for manipulation and processing of droplets / plugs / slugs in small volumes (10-6 - 10-15 L) transported in an immiscible phase Emulsion in micro channel Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 6 8.1 Introduction V8 www.bioscience.org Droplets / Plugs / Slugs in Microchannel  Typically: Two immiscible phases in microchannel  Emulsion is formed  2-phase gas - liquid or liquid - liquid  3-phase liquid - liquid with surfactant between the phases  Most-used combination: oil and water with a surfactant Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 7 8.1 Introduction Definition of Terms  W / O Water droplet in Oil  O / W Oil droplet in Water Dispersed phase / Continuous phase Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 www.bioscience.org 8 V8 8.2 Properties Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 9 8.2 Properties V8 10 Droplet / Plug in Micro Channel  Stable compartment with nL to fL volume  Typically no diffusion through interface  Pressure-driven transport through channel www.bioscience.org  If oil is continuous phase → hydrophobic channel walls necessary  If water is continuous phase → hydrophilic channel walls necessary Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.2 Properties V8 11 Often Used Oils  Silicone oils DC 200, PDMS, AR 200  Hydrocarbon oils Hexadecan, Tetradecan, Oktadecan, Dodecan, mineral oils, Isopar M, cooking oil  Fluorocarbon oils Perfluorohexan (PFH), Perfluorocyclohexan (PFC), Perfluorodecaline (PFD), Perfluoroperhydrophenanthrene (PFPH), HFE (7100, 7200, 7500), FC (40, 70, 77, 3283) → Choice of oil depends on application → Viscosity influences the formation of droplets / plugs → Fluorocarbon oils are advantages against hydrocarbon oils  Show enhanced O2 permeability  Non-soluble with organic compounds Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.2 Properties W/O: V8 12 Surfactant / Wetting Agent  Water droplets tend to coagulate easily  Addition of wetting-agent  Increases stability of droplet / plug / slug  Prevents coagulation  Establishes  Biological inert inner surface of droplet / plug /slug or  Bioactive inner droplet / plug / slug surface for biochemical reactions → Highly complex topic, see references R.C. Luo et al.: Soft 1 1-23 (2012) J-C. Baret: Lab Chip 12 422 (2012) C. Holtze: Lab Chip 8 1632-1639 (2008) R. Seemann et al.: Rep.Prog. Phys. 75 016601 (2012) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 https://www.fkp.tu-darmstadt.de/groups/ag_stuehn/ 8.2 Properties V8 13 Often Used Surfactants for  Hydrocarbon oils e.g. Span 80, Abil® EM900, Tween 20  Fluorocarbon oils e.g. Block-Copolymer PFPE-PEG PFPE … Perfluoro-polyether long tail ( in oil phase) PEG* … Polyethylene glycol head (in water droplet) * R.C. Luo et al.: Soft 1 1-23 (2012) Will often be replaced by cheaper Jaffamine® ED-900 (PEG-based poly(etheramine)) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.2 Properties V8 14 Be aware: Diffusion can sometimes take place from one droplet to the neighbored ones through the continuous phase W/O Water droplets Fluorinated oil HFE-7500 including resorufin fluorophore including PFPE-PEG-PFPE surfactant 0h 1.5 h 3h 6h 12 h 24 h P. Gruner,.., J.C. Baret: Nature Comm. 7 10392 (2016) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.2 Properties V8 15 The reason is that with the surfactant  Surface tension decreases at the interface  Bonding strength of interface molecules decreases  Electrical neutral molecules can more easily diffuse through the interface 0h 1.5 h 3h 6h 12 h 24 h Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 8.3 Formation of Droplets / Plugs Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 16 8.3 Formation of Droplets / Plugs V8 17 Formation of Droplets / Plugs Using Passive Structures T-Junction Flow Focusing C.N. Baroud et al.: Lab Chip 10 2032-2045 (2010) R. Seemann et al.: Rep. Prog. Phys. 75 016601 (2012) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 Coaxial Injection 8.3 Formation of Droplets / Plugs V8 Formation of Droplets by Two Stress Factors at Interface  Interface tension Contraction/Compression of interface  Viscous shear stress Stretching of interface Pulls interface downstream → Destabilization of interface → Formation of droplet / plug / slug C.N. Baroud et al.: Lab Chip 10 2032-2045 (2010) R. Seemann et al.: Rep. Prog. Phys. 75 016601 (2012) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 18 V8 8.3.1 Capillary Number Ca Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 19 8.3.1 Capillary Number Ca Capillary Number Ca V8 ηC  vC viscous shear stress Ca   σ interface tension Ca is the Characteristic Number for Droplets Under Shear Forces  Ca < 1: Interface tension is dominant Interface is formed with minimum surface area  Ca > 1: Viscous shear stress is dominant Droplet deforms/stretches ηC … Viscosity of the continuous fluid (Pa·s) vC … Velocity of the continuous fluid (m/s) σ …. Interface tension (N/m) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 20 V8 8.3.2 T-Junction Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 21 8.3.2 Droplet Formation at T-Junction T-Junction For Small Flow Rates of Continuous Phase: Squeezing V. van Steijn et al: Lab Chip 10 2513-1518 (2010) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 22 8.3.2 Droplet Formation at T-Junction V8 23 For Small and Medium Flow Rates of Continuous Phase: Squeezing and Dripping Ca  η  v viscous shear stress  σ interface tension http://www.youtube.com/watch?v=SoH97_zclK8 A.R. Abate et al.: Lab Chip 12 1516-1521 (2012) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.3.2 Droplet Formation at T-Junction V8 24 w = 100 µm win = 50 µm h = 33 µm L L Qwater  1  w Qoil α is a constant of order one, whose particular value depends on the geometry of the T-junction. P. Garstecki et al.: Lab Chip 6 437-446 (2006) T. Glawdel et al: Phys. Rev. 85 016322 (2012) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 Q … Volume flow rate 8.3.2 Droplet Formation at T-Junction V8 Common Parameters Affecting the Droplet Formation at T-Junctions Ca   Capillary number  Flow rate ratio QD QC  Viscosity ratio D C ηC  vC viscous shear stress  σ interface tension  Channel width ratio wD wC  Aspect ratio h wC X.-B. Li et al.: Chem. Eng. 69 340-351 (2012) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 25 8.3.2 Droplet Formation at T-Junction http://www.youtube.com/watch?v=aJWckIGi5OE Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 26 8.3.2 Droplet Formation at T-Junction Plug Generation at T-Junction with Different Angles https://www.youtube.com/watch?v=aysInwrMyeM Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 27 8.3.2 Droplet Formation at T-Junction V8 28 Squeezing Ca ~ 0.6 Dripping medium flow rates* Jetting high flow rates* * Of continuous phase ηC  vC viscous shear stress Ca   σ interface tension P. Garstecki et al.: Lab Chip 6 437-446 (2006) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 Increasing Ca Small flow rates* 8.3.2 Droplet Formation at T-Junction V8 29 Double (Multi-) Emulsions  Droplet size and cutting rate tunable through  Flow rates  Channel dimensions  Ca In general  W/O → hydrophobic channel wall  O/W → hydrophilic channel wall T. Nisisako et al.: Soft Mat. 1 23-27 (2005) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.3.2 Droplet Formation at T-Junction V8 100 µm 50 µm 50 µm Double (Multi-) Emulsions Cutting rate: 22 droplets / s T. Nisisako et al.: Soft Mat. 1 23-27 (2005) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 30 V8 8.3.3 Flow Focusing Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 31 8.3.3 Droplet Formation by Flow Focusing V8 Flow Focusing In hydrodynamic focusing arrangement, dispersed phase is squeezed at a constriction water air water air water G. Whitesides Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 out 32 8.3.3 Droplet Formation by Flow Focusing https://www.youtube.com/watch?v=RQWbu7CZzTQ Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 33 8.3.3 Droplet Formation by Flow Focusing V8 34 Q0 … Rate of sheath flow Qi …. Flow rate of inner medium Flow Focusing Time Time interval of pictures: 1 ms Oil Wo=278 µm Water Wi=197 µm Oil Wo Wi=963 µm D=44m Hf=161 µm Channel height h = 105 m S.L. Anna et al.: Appl. Phys. Lett. 82 (3) 364-366 (2003) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 a) Qo = 8.3*10-5 ml/s; Qi /Qo= 1/4 b) Qo = 4.2*10-4 ml/s; Qi /Qo= 1/40 8.3.3 Droplet Formation by Flow Focusing https://www.youtube.com/watch?v=HYQr43l5c7U Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 35 8.3.3 Droplet Formation by Flow Focusing Double- (Multi-) Emulsions C.H. Chen et al.: Advanced Materials 21 (31) 3201-3204 (2009) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 36 V8 8.3.4 Coaxial Injection Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 37 8.3.4 Droplet Formation by Coaxial Injection V8 Coaxial Injection < co-flow > Channel l … 200 mm w … 2.5 mm h … 20 mm C. Cramer et al.: Chem. Eng. Sci. 59 (15) 3045-3058 (2004) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 38 8.3.4 Droplet Formation by Coaxial Injection V8 Droplet Formation at Junction Droplet Formation in Jet Stream (dripping) (jetting) Cutting length C. Cramer et al.: Chem. Eng. Sci. 59 (15) 3045-3058 (2004) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 39 V8 40 Coaxial Injection Droplet Formation During Jetting www.mech2262.drupalgardens.com - Plateau-Rayleigh Instabilities Joseph Plateau (1801 – 1883) jackgreen5149.blogspot.de 8.3.4 Droplet Formation by Coaxial Injection  Becomes sinusoidal  Is unstable  Decays after a certain time Page from Plateau‘s book (1873) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 en.wikipedia.org/ Cylindrical Jet John William Strutt 3rd Baron Rayleigh (1842 – 1919) 8.3.4 Droplet Formation by Coaxial Injection Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 41 https://www.youtube.com/watch?v=X3PdtK5it5o/ https://www.youtube.com/watch?v=cYNsSkGNp1U J. Plateau: Experimental and Theoretical Statics of Liquids Subject to Molecular Forces Only. Paris: Gauthier-Villars (1873) L. Rayleigh: Proc. London Math. Soc. 10 (4) 4-13 (1878) L. Rayleigh: Proc. R. Soc. Lond. 29:71–97 (1879) L. Rayleigh: Philos. Mag. 14:184–86 (1882) L. Rayleigh: Philos. Mag. 34:145–54 (1892) V8 8.3.4 Droplet Formation by Coaxial Injection V8 42 Assumption: Jet shape is sinusoidal pLaplace  1 1        R1 R2  Effect 1 (correlated to jet radius R1)  In wave trough: jet radius is smaller → Laplace pressure is higher  In wave peak: jet radius is larger → Laplace pressure due is smaller Result: High Laplace pressure in trough presses fluid in wave peak Wave amplitude increases Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.3.4 Droplet Formation by Coaxial Injection pLaplace  1 1        R1 R2  V8 43 Effect 2 (correlated to jet radius R2)  With falling jet, R2 decreases in though and peak  In wave trough → Laplace pressure increases in the air phase → Laplace pressure decreases in the liquid phase  In wave peak → Laplace pressure increases in the liquid phase Result: High pressure in peak presses fluid in wave trough Wave amplitude decreases Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.3.4 Droplet Formation by Coaxial Injection V8  Effect 1 is Opposite to Effect 2  Competition: Effects do not balance  Flow inside the jet is proportional  to the pressure gradient,  NOT to pressure difference  A thin jet of a liquid is unstable to disturbances with wavelengths   2  R0 and break into droplets  Break up into droplets at   9.02  R0  Break up time   R03  0  2.74  For thin jets Negligible gravitation Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 44 8.3.4 Droplet Formation by Coaxial Injection V8 45 Coaxial Injection  Low vcont → dripping  High vcont → jetting Cutting length  Increase of vcont  ↑ Cutting length  ↑ Number of droplets per time  ↓ Droplet formation time  ↓ Droplet diameter vcont < vcont  ↑ Number of satellite droplets C. Cramer et al.: Chem. Eng. Sci. 59 (15) 3045-3058 (2004) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.3.4 Droplet Formation by Coaxial Injection Double- (Multi-) Emulsions L.Y. Chu et al.: Angewandte Chemie International Edition 56 (47) 8907-8974 (2007) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 46 V8 8.3.5 Inclined Cover Plate Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 47 8.3.5 Droplet Formation by Inclined Cover Plate V8 48 Generation of Droplets α = 0° α = 1.2°. No volume flow rate Vcont of continuous phase needed ! R. Dangla et al.: PNAS 110 (3) 853-858 (2013) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.3.5 Droplet Formation by Inclined Cover Plate R.Dangla et al.: PNAS 110 (3) 853-858 (2013), video in supplementary information Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 49 8.3.5 Droplet Formation by Inclined Cover Plate R.Dangla et al.: PNAS 110 (3) 853-858 (2013), video in supplementary information Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 50 8.3.5 Droplet Formation by Inclined Cover Plate V8 51 Rd ….. Droplet radius Q …… Flow rate R. Dangla et al.: PNAS 110 (3) 853-858 (2013) R. Dangla is CTO of Stilla Technologies https://www.stillatechnologies.com Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.4 Pressure in Microchannels with Plugs 8.4 Pressure in Micro Channels with Plugs Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 52 8.4 Pressure in Microchannels with Plugs V8 53 Micro Channel With Homogeneous Filling  Laminar flow  Volume flow rate ~ pressure gradient inlet Hagen-Poiseuille for a cylindrical channel (see V4) p  8   L Q 4   r0 l,w,h … Dimensions of channel η…….. Viscosity Q …….Volume flow rate pinlet poutlet Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 outlet 8.4 Pressure in Microchannels with Plugs V8 54 Δp Outlet Inlet Continuous phase Plug Continuous phase Plug =Slug p  pcont.  p plug  pLaplace  Zones be described by HagenPoiseuillle’s law  Laplace pressure arises at interface due to meniscus Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 8.4 Pressure in Microchannels with Plugs In flow direction for a circular tube pLaplace,r  2 cos r R pLaplace V8 pLaplace,a   2 cos a R 2  (cos r  cos  a ) R J.Berthier and P. Silberzahn: ISBN 1-58053-961-0 Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 55 8.4 Pressure in Microchannels with Plugs V8 56 Non-viscous plug Plugs in Micro Channels result in discontinuous pressure drops  Linear pressure drop in Δpcont continuous phase and Δpplug Δpcont Δpplug λ >> 1 Viscous plug plug (Hagen-Poiseuille)  Discrete pressure jumps at interfaces (Laplace) C.N. Baroud et al.: Lab Chip 10 2032-2045 (2010) Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 Δpcont disp  cont 8   L p  Q 4   r0 Conclusion V8 57 Conclusion Droplets / Plugs in Micro Channels Advantages  Tiny self-contained compartments with defined volume in nL-/fL range  Low reagent consumption  Modification of inner plug / droplet surfaces by surfactants is possible Disadvantages  Pressure driven platform  External pumps and reservoirs necessary  High-speed cameras for recording necessary  Oil phase prevents evaporation  Used for high-throughput applications  Alternative to micro titer plate technology Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 V8 One Minute Paper 1. What was the most important topic you understood? 2. What was the topic you didn‘t catch? Lecture „Microfluidic Systems - Bio-MEMS“ - Droplets Prof. Dr.-Ing. Uwe Schnakenberg | Institute of Materials in Electrical Engineering 1 | WS 23 58