Spreading of Normal Liquid Helium Drops

Area of Science:

• Physics
• Fluid Dynamics
• Low-Temperature Physics

Background:

• Understanding the behavior of superfluids like helium-4 is crucial for fundamental physics.
• Investigating drop dynamics on solid surfaces provides insights into wetting phenomena and surface interactions.

Purpose of the Study:

• To investigate the dynamics of spreading for drops of helium-4 on a solid surface.
• To analyze the temperature-dependent behavior of these drops, from near the critical point to near the lambda point.

Main Methods:

• Utilized video imaging techniques to capture the spreading dynamics.
• Employed interferometric methods for precise measurements.
• Conducted experiments across a temperature range of 5.2 K to 2.2 K.

Main Results:

• Observed drops forming a pancake shape after an initial transient phase.
• Determined the spreading radius follows R(t)≈t^α, with α=0.149±0.002.
• Noted drops shrink due to evaporation, limiting their lifetime to approximately 1000 seconds.
• Identified a visible contact line with a contact angle of about one degree, despite complete wetting.

Conclusions:

• The study quantifies the spreading dynamics of helium-4 drops, providing a power-law relationship for radius growth.
• Evaporation significantly influences the drop lifetime and ultimate behavior.
• The presence of a distinct contact line, even in a complete wetting scenario, highlights complex surface phenomena.