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Drops on patterned surfaces Halim Kusumaatmaja Alexandre Dupuis Julia Yeomans. Summary. The model Chemically patterned surfaces Spreading on stripes Hysteresis Superhydrophobic surfaces Introduction Hysteresis
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Drops on patterned surfaces Halim Kusumaatmaja Alexandre Dupuis Julia Yeomans
Summary The model Chemically patterned surfaces Spreading on stripes Hysteresis Superhydrophobic surfaces Introduction Hysteresis Transitions between states Dynamics
Equations of motion Navier-Stokes equations continuity Navier-Stokes No-slip boundary conditions on the velocity
Equilibrium free energy bulk term interface free energy surface term Van der Waals controls surface tension controls contact angle
Controlling the contact angle Surface free energy Minimising the free energy leads to: Boundary condition on the Euler-Lagrange equation A relation between the contact angle and the surface field
Summary The model Chemically patterned surfaces Spreading on stripes Hysteresis Superhydrophobic surfaces Introduction Hysteresis Transitions between states Dynamics
LB simulations on substrate 4 • Two final (meta-)stable state observed depending on the point of impact. • Dynamics of the drop formation traced. • Quantitative agreement with experiment. Simulation vs experiments Evolution of the contact line
LB simulations on substrate 4 • Two final (meta-)stable state observed depending on the point of impact. • Dynamics of the drop formation traced. • Quantitative agreement with experiment. Simulation vs experiments Evolution of the contact line
Two wide stripes: 110o /130o hydrophilic hydrophobic hydrophilic
Summary The model Chemically patterned surfaces Spreading on stripes Hysteresis Superhydrophobic surfaces Introduction Hysteresis Transitions between states Dynamics
Hysteresis slips at angle advancing
Hysteresis pinned until
Hysteresis pinned until
Hysteresis slips smoothly across hydrophobic stripe
Hysteresis slips smoothly across hydrophobic stripe
Hysteresis jumps back to
Hysteresis advancing stick slip jump (slip)
Hysteresis advancing stick slip jump (slip) receding stick (slip) jump slip
(Hysteresis) loop a a a contact angle volume advancing contact angle receding contact angle
(Hysteresis) loop slip jump stick contact angle volume advancing contact angle receding contact angle
Hysteresis: 3 dimensions A. squares 60o background 110o B. squares 110o background 60o
Hysteresis: 3 dimensions A B squares hydrophilic squares hydrophobic
Hysteresis: 3 dimensions macroscopic contact angle versus volume A B stick jump
Hysteresis: 3 dimensions macroscopic contact angle versus volume A B 94o 92o 110/60
Hysteresis on chemically patterned surfaces 1.Slip, stick, jump behaviour, but jumps at different volumes in different directions (but can be correlated) 2. Contact angle hysteresis different in different directions 3. Advancing angle (92o) bounded by qmax (110o) Receding angle (80o) bounded by qmin (60o) 4. Free energy balance between surface / drop interactions and interface distortions determines the hysteresis
Summary The model Chemically patterned surfaces Spreading on stripes Hysteresis Superhydrophobic surfaces Introduction Hysteresis Transitions between states Dynamics
Two drop states suspended drop collapsed drop He et al., Langmuir, 19, 4999, 2003
Suspended and collapsed drops Suspended, q~160o Collapsed, q~140o Homogeneous substrate, qeq=110o