Surface textures suppress viscoelastic braking on soft substrates

Area of Science:

• Soft matter physics
• Fluid dynamics
• Surface science

Background:

• Droplets on compliant substrates experience viscoelastic braking, slowing their motion due to solid deformation at the contact line.
• This braking effect arises from energy dissipation within the deforming solid material.

Purpose of the Study:

• To investigate how surface textures influence droplet behavior on compliant substrates.
• To determine if textures can mitigate or suppress viscoelastic braking.
• To explore the role of capillary stresses and contact line dynamics on textured soft surfaces.

Main Methods:

• Fabrication of patterned compliant substrates.
• Confocal microscopy to observe texture deformation and contact line behavior.
• High-speed microscopy to measure droplet velocities.
• Computational analysis of pillar deflection and energy dissipation.

Main Results:

• The superhydrophobic Cassie state is maintained on soft textured surfaces.
• Capillary stresses deform textured elements, inducing liquid pinning.
• Textured surfaces require greater initial force for droplet motion compared to flat surfaces.
• Droplet velocities on textured (soft or hard) and flat substrates are similar, indicating suppression of viscoelastic braking.
• High contact line velocities on textures lead to reduced solid deformation and dissipation.

Conclusions:

• Surface textures can suppress viscoelastic braking on compliant substrates by enabling rapid contact line motion.
• Texture-induced contact line geometry and scale are crucial for mitigating energy dissipation in the solid.
• Pillar deflection at the receding contact line does not impede overall droplet motion.