Inkjet Printing of P-OLED Displays Microdrop Impact & Spreading
Modelling: Why Bother? 1 - Recover Hidden Information 2 - Map Regimes of Spreading 3 – Experiment Millimetres in Milliseconds - Rioboo et al (2002) Microns in Microseconds - Dong et al (2002) Flow Inside Solids – Marston et al 2010
r Pasandideh-Fard et al 1996 Dynamic Contact Angle Required as a boundary condition for the free surface shape. r t
Speed-Angle Formulae R σ1σ1 σ 3 - σ 2 Young Equation Dynamic Contact Angle Formula ) U Assumption: A unique angle for each speed
Physics of Dynamic Wetting Make a dry solid wet. Create a new/fresh liquid-solid interface. Class of flows with forming interfaces. Forming interface Formed interface Liquid-solidinterface Solid
Relevance of the Young Equation R σ 1e σ 3e - σ 2e Dynamic contact angle results from dynamic surface tensions. The angle is now determined by the flow field. Slip created by surface tension gradients (Marangoni effect) θeθe θdθd Static situationDynamic wetting σ1σ1 σ 3 - σ 2 R
In the bulk: On liquid-solid interfaces: At contact lines: On free surfaces: Interface Formation Model θdθd e2e2 e1e1 n n f (r, t )=0 Interface Formation Modelling
JES &YDS 2011, Viscous Flows in Domains with Corners, CMAME JES & YDS 2012, Finite Element Framework for Simulating Dynamic Wetting Flows, Int. J. Num. Meth Fluids. JES & YDS, 2012, Finite Element Simulation of Dynamic Wetting Flows as an Interface Formation Process, to JCP. JES & YDS, 2012, The Dynamics of Liquid Drops and their Interaction with Surfaces of Varying Wettabilities, to PoF.
Washburn Model Basic Dynamic Wetting Models Interface Formation Model and Experiments Equilibrium Dynamic Equilibrium Dynamic Equilibrium Dynamic Meniscus Meniscus shape unchanged by dynamic wetting Meniscus shape dependent on speed of propagation. Hydrodynamic Resist: Meniscus shape influenced by geometry Summary: Dynamic Wetting Models
Capillary Rise: Models vs Experiments Compare to experiments of Joos et al 90 and conventional Lucas-Washburn theory Lucas-Washburn assumes: Poiseuille Flow Throughout Spherical Cap Meniscus Fixed (Equilibrium) Contact Angle
Lucas-Washburn vs Full Simulation R = 0.036cm; every 100secs R = 0.074cm; every 50secs
Comparison to Experiment Full Simulation Washburn JES & YDS 2012, to JCP
Wetting as a Microscopic Process: Flow through Porous Media
Micro: Pore scale dynamics of: Menisci in wetting front Ganglia Macro (Darcy-scale) dynamics of: Entire wetting front Ganglia in multiphase system Multi-scale porosity: Motion on a microporous substrate
Wetting: Micro-Macro Coupling Spreading on a Porous Medium
Current State of Modelling 1) Contact Line Pinned 2) Shape Fixed as Spherical Cap
The Reality Equilibrium shape is history-dependent.
Spreading on a Porous Substrate θDθD θwθw U θdθd
No equilibrium angle to perturb about Final shape is history dependent Approach Use continuum limit (separation of scales) Consider flow near contact line Find contact angles as a result: θDθD θwθw U YDS & JES 2012, to JFM
Flow Transition Formula is when contact lines coincide Example: Transition when
Potential Collaboration Drop Impact Microdrops on impermeable surfaces Drops on permeable/patterned surfaces Capillary Rise Investigation of ‘resist’ mechanism in micro/nano regimes Flow with Forming/Disappearing Interfaces Coalescence, bubble detachment, jet break-up, cusp-formation, etc. Porous Media Investigation of newly developed model
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