Microfluidic Free-Surface Flows: Simulation and Application The University Of Birmingham J.E Sprittles Y.D. Shikhmurzaev Indian Institute of Technology, Mumbai November 5th 2011
Worthington’s Sketches Millimetre sized drops of milk on smoked glass.
Millimetre Drop Impact 1 2 3 4 Courtesy of Romain Rioboo
Flow Control Using Chemically Patterned Solids Hydrophobic Hydrophilic
Inkjet Printing: Impact of Microdrops • 100 million printers sold yearly in graphic arts. • Drops ejected have: • Radius ~ 10microns • Impact ~ 10m/s • Surface physics are dominant. • Inkjet printing is now replacing traditional fabrication methods...
Inkjet Printing of P-OLED Displays Microdrop Impact & Spreading
Why Develop a Model? • - Recover Hidden Information • - Map Regimes of Spreading 3 – Experiment Rioboo et al (2002) Dong et al (2002)
The Contact Angle • Contact angle is required as a boundary condition for the free surface shape. r r t Pasandideh-Fard et al 1996
Conventional Approach – Contact Angle ) U Dynamic Contact Angle Formula Young Equation σ1 σ3 - σ2 Assumption: A unique angle for each speed R
Is the Angle Always a Function of the Speed?(Experiments of Bayer & Megaridis 06) 1mm Water )
Hydrodynamic Assist to Wetting U U, cm/s Controlled Flow Rate Blake & Shikhmurzaev 02
The Simplest Model of Interface Formation (Shikhmurzaev 93) In the bulk: Interface Formation Model Conventional Model On free surfaces: On liquid-solid interfaces: At contact lines:
The Spine Method for Free Surface Flows Nodes define free surface. The Spine Nodes fixed on solid.
Arbitrary Lagrangian-Eulerian Mesh Design • Spines are Bipolar • Free Surface Captured Exactly JES & YDS 2011, Int. J. Num. Meth. Fluids ; JES & YDS 2011, Submitted to J. Comp. Phys.
Oscillating Drops: Code Validation For Re=100, f2 = 0.9 JES & YDS 2011, MNF, In Print
Pressure Behaviour for Obtuse Angles The pressure plot from a typical simulation.
Testing Ground: Flow in a Corner U U In frame moving with contact line. In frame fixed with solid.
Viscous Flow in a Corner Spurious COMSOL ‘Solution’ Our FEM Solution JES & YDS 2011, IJNMF 65; JES & YDS 2011, CMAME 200
Microdrop Spreading from Rest(Capillarity Driven Spreading) Pressure Scale Apex Velocity Scale Capillary Wave
Microdrop Impact and Spreading Pressure Scale Velocity Scale
Speed – Angle Relationships:Comparison of IFM with Conventional Model. Jump in Contact Line Speed Rest (IFM) Increase in Contact Line Speed Impact (IFM) Conventional Model. 0.01 1 100 Jiang et al 79
Early Stages of Spreading 2.2 m/s 4.4 m/s 12.2 m/s
Impact on a Surface of Variable Wettability 4m/s Impact 5m/s Impact
Current Research: Dynamics at Different Scales Millimetre Drop Microdrop Nanodrop
Current Research:Unexplained Phenomena in Coating Processes Ca Simpkins & Kuck 03
Current Research: Nanofluidics “While inertial effects may also be important, the influence of the dynamic contact angle should not be ignored.” (Martic et al 02)
Future Research: Pore Scale Dynamics Wetting Mode Threshold Mode
Future Research: Additional Physical Effects Liquid-Liquid Displacement Surfactant Transport
Future Research: Impact on Powders Mitchinson (2010) Marston et al (2010) Aussillous & Quéré (2001)
Qualitative Test: Pyramidal Drops (mm size drop) Experiment Renardy et al.
Future Research: Multi-Physics Platform ) • Multiphysics Platform + • Dynamic Wetting Patch
Hysteresis of the Dynamic Contact Angle • Hyteresis: Receding angle • No hysteresis
Analytic Progress: When Does ? High Impact Speed Small Drops Stokes Region (viscous forces dominate inertial forces) Length of interface formation process Slow Spreading of Large Drops