Visualization and Experimental Characterization of Wrapping Layer Using Planar Laser-Induced Fluorescence.

Area of Science:

• Surface Science
• Fluid Dynamics
• Materials Science

Background:

• Nanotextured oil-impregnated surfaces exhibit ultralow droplet adhesion and high mobility.
• Applications include enhanced condensation, reduced drag, and anti-biofouling, but lubricant depletion is a key industrial concern.

Purpose of the Study:

• Investigate the source of lubricant depletion in oil-impregnated surfaces.
• Visualize and quantify the oil layer (wrapping layer) surrounding droplets.
• Identify strategies to mitigate lubricant loss.

Main Methods:

• Planar laser-induced fluorescence (PLIF) to visualize and measure the oil wrapping layer thickness.
• Experimental analysis of silicone oil and mineral oil behavior on nanotextured surfaces.
• Scaling analysis balancing capillary and van der Waals forces.

Main Results:

• Silicone oil forms a nonuniform wrapping layer on water droplets due to interfacial force imbalance.
• The average thickness of the silicone oil wrapping layer is approximately 50 ± 10 nm.
• Mineral oil does not form a wrapping layer on water droplets under similar conditions.

Conclusions:

• The wrapping layer of silicone oil is a primary contributor to lubricant depletion.
• Mineral oil's lack of wrapping layer formation presents a viable strategy to enhance lubricant retention.
• Findings aid in understanding and quantifying lubricant depletion for improved condensation and water harvesting technologies.