Direct visualization of particle attachment to a pendant drop

Area of Science:

• Fluid dynamics
• Colloid science
• Surface science

Background:

• Understanding particle-liquid interactions is crucial for various applications, including the formation of liquid marbles.
• The rapid dynamics of particle attachment to liquid drops, particularly the 'snap-in' effect, remain incompletely understood.

Purpose of the Study:

• To experimentally investigate the attachment dynamics of a single particle to a liquid drop.
• To elucidate the underlying physical mechanisms governing the snap-in effect and subsequent lift-off.
• To quantify key parameters like contact angle, wetted radius, and forces involved.

Main Methods:

• High-speed videography was employed for direct visualization of the particle-drop interaction.
• High-magnification imaging allowed for tracking the contact line evolution around the particle.
• Dynamic features were extracted from video data to analyze wetting and forces.

Main Results:

• The 'snap-in' effect was observed to occur on sub-millisecond timescales.
• The early wetting stage was identified as inertial-dominated, following a power-law relation: ϕ ∼ (t/τ)^α.
• Lift-off forces were measured to be in the range of 1-100 μN, consistent with theoretical predictions based on weight and capillary forces.

Conclusions:

• The study provides a fundamental understanding of the rapid particle attachment process to liquid drops.
• The measured lift-off forces explain the facile formation of liquid marbles during droplet impact.
• The findings contribute to the broader knowledge of interfacial phenomena and particle manipulation in liquids.