Slow spreading with a large contact angle on hygroscopic materials

Area of Science:

• Materials Science
• Wood Physics
• Fluid Dynamics

Background:

• Water transfer in timber structures is crucial but not fully understood.
• Wetting and imbibition processes in wood require further investigation.

Purpose of the Study:

• To investigate the physics of water droplet behavior on wood surfaces.
• To explain the observed large initial contact angle and slow spreading of water on wood.

Main Methods:

• Contact angle measurements on wood and hydrogel surfaces.
• Analysis of surface deformation and water diffusion effects.

Main Results:

• Water drops on air-dry wood exhibit an initial contact angle >90°, decreasing over time.
• Hydrogels show similar behavior, with initial large contact angles due to localized swelling.
• Wood surface deformation and swelling pin the contact line, causing initial high contact angles.

Conclusions:

• Wood surface deformation and swelling explain the initial high contact angle and slow water spreading.
• The phenomenon involves the contact line pinning and unpinning as water diffuses.
• Findings offer insights into water transfer mechanisms in wood and related materials.