Marangoni force-driven manipulation of photothermally-induced microbubbles

Area of Science:

• Physics
• Materials Science
• Microfluidics

Background:

• Microbubbles are crucial in various applications, but their precise manipulation remains challenging.
• Laser-induced thermal gradients offer a non-contact method for generating forces.
• Surface tension gradients (Marangoni force) are known drivers of fluid motion.

Purpose of the Study:

• To present a novel method for generating and manipulating microbubbles using laser-induced thermal gradients.
• To investigate the underlying physics of microbubble movement driven by temperature gradients.
• To quantify the forces involved in laser-induced microbubble manipulation.

Main Methods:

• Utilizing a 1064 nm laser beam split and coupled into two optical fibers.
• Photo-depositing silver nanoparticles on optical fiber tips to absorb laser light.
• Inducing localized thermal gradients in an ethanol solution to generate microbubbles.
• Employing theoretical and experimental studies to analyze microbubble migration.

Main Results:

• Successful generation of microbubbles at optical fiber tips in non-absorbent liquids.
• Demonstrated controlled migration of microbubbles between fiber tips by switching thermal gradients.
• Estimated a maximum Marangoni force of 400 nN for a 110 μm radius microbubble.
• Validated the Marangoni force as the primary driving mechanism for microbubble manipulation.

Conclusions:

• Laser-induced thermal gradients provide an effective means for microbubble generation and manipulation.
• The Marangoni effect is the key force enabling controlled microbubble movement.
• This technique offers potential for precise micro-manipulation in microfluidic systems.