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Drops on patterned surfaces Halim Kusumaatmaja Alexandre Dupuis Julia Yeomans

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## Drops on patterned surfaces Halim Kusumaatmaja Alexandre Dupuis Julia Yeomans

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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