Launching a Drop via Interplay of Buoyancy and Stick-Jump Dissolution

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Materials Science

Background:

• Archimedes' principle typically dictates that buoyancy is dependent on object size and density relative to the fluid.
• Dissolving objects in solutions can exhibit complex behaviors influenced by chemical reactions and fluid interactions.
• Understanding drop dynamics is crucial for applications in microfluidics and material processing.

Purpose of the Study:

• To investigate a novel phenomenon of a dissolving drop exhibiting delayed rise in an aqueous acid solution.
• To elucidate the key physical mechanisms governing the spontaneous upward movement of a dissolving drop.
• To explore the potential of this programmable drop rise for microscale engineering applications.

Main Methods:

• Observation and analysis of a dissolving polymer solution drop on a substrate in an aqueous acid medium.
• Characterization of drop dissolution, microdroplet formation, and interaction with the surrounding fluid.
• Identification of critical factors, including stick-jump behavior and Archimedean number, influencing drop dynamics.

Main Results:

• A dissolving drop rises only after reaching a significantly smaller size, contrary to expected buoyancy behavior.
• The drop rise is initiated by a combination of stick-jump dissolution and sufficient buoyancy force (Archimedean number > 1).
• The timing of the drop rise is controllable by the initial drop size and its chemical reaction rate.

Conclusions:

• A new mechanism for programmable drop rise has been discovered, driven by chemical dissolution and fluid dynamics.
• This phenomenon offers a novel method for controlled movement of microscale objects in dense media.
• Potential applications include microfluidics, microrobotics, and device engineering, utilizing spontaneous drop detachment.