Promoting rotation, friction, and mixed lubrication for particles rolling on microstructured surfaces

Area of Science:

• Fluid dynamics
• Surface science
• Microscale phenomena

Background:

• Understanding sphere motion on patterned surfaces is crucial for microfluidics and tribology.
• Flooded conditions and low Reynolds numbers present unique challenges in predicting particle dynamics.

Purpose of the Study:

• To investigate the impact of microstructure aspect ratio on sphere rolling and slipping.
• To determine how surface features like height, coverage, and geometry affect sphere motion.
• To validate a physical model for sphere motion on patterned surfaces.

Main Methods:

• Studying arrays of rigid microstructures with varying aspect ratios and surface coverages.
• Analyzing sphere motion under flooded conditions at low Reynolds numbers.
• Employing sliding friction measurements using a force microscope.

Main Results:

• Increased microstructure height leads to higher sphere rotational velocities.
• A superposition model of resistance functions accurately predicts sphere motion across different surface coverages and geometries.
• Microstructure effects on friction become more significant with increasing Hersey numbers.

Conclusions:

• Sphere motion on patterned surfaces is highly dependent on microstructure geometry, particularly height.
• The developed physical model effectively captures the complex interactions between spheres and patterned surfaces.
• Friction plays a critical role, and its dependence on microstructure increases with the Hersey number.