Boundary conditions for soft glassy flows: slippage and surface fluidization

Area of Science:

• Rheology
• Soft Matter Physics
• Surface Science

Background:

• Understanding surface boundary conditions is crucial for fluid dynamics.
• Dense emulsions exhibit complex flow behaviors near interfaces.
• Surface properties significantly influence macroscopic flow characteristics.

Purpose of the Study:

• To investigate the impact of controlled surface roughness on dense emulsion flow.
• To quantify slip velocity and shear rate at the wall.
• To explore the phenomenon of surface fluidization in relation to roughness.

Main Methods:

• Utilized microlithographic tools to fabricate surfaces with precise roughness patterns.
• Employed dynamic confocal microscopy for in-situ measurements.
• Measured slip velocity and shear rate near the wall.

Main Results:

• Both slippage and wall fluidization demonstrated a non-monotonic dependence on surface roughness.
• Observed a correlation between roughness patterns and the emergence of slip and fluidization.
• Identified a critical role of surface-induced phenomena in emulsion flow.

Conclusions:

• Surface roughness is a key parameter controlling boundary conditions in dense emulsion flow.
• The observed non-monotonic behavior can be explained by a model involving stratified layers and plastic event activation.
• Surface fluidization is a direct consequence of specific surface roughness features.