Monitoring picoliter sessile microdroplet dynamics shows that size does not matter

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Materials Science

Background:

• Arrayed picoliter-size sessile microdroplets of aqueous phase in oil are utilized in various scientific applications.
• Understanding microdroplet dissolution dynamics is crucial for controlling experiments in confined volumes.

Purpose of the Study:

• To monitor and analyze the dissolution process of picoliter-size aqueous microdroplets in oil.
• To compare the dissolution dynamics of microdroplets with the evaporation dynamics of larger droplets.
• To establish a model for predicting microdroplet concentration during dissolution.

Main Methods:

• Utilized a recently developed fluidic device for generating arrayed picoliter-size sessile microdroplets.
• Monitored microdroplet dissolution by observing changes in height and contact angle.
• Measured dissolution rates across different aqueous solutions.

Main Results:

• Observed initial pinning of microdroplet perimeters, leading to constant contact diameters.
• Demonstrated that microdroplet contraction occurs via reductions in height and contact angle.
• Confirmed comparable dissolution dynamics between picoliter microdroplets in oil and microliter droplet evaporation in air.
• Found a constant microdroplet dissolution rate irrespective of the aqueous solution.

Conclusions:

• The dissolution of picoliter microdroplets in oil follows predictable dynamics governed by selective water diffusion.
• The observed dissolution rate is constant and can be modeled, offering precise concentration determination.
• This model has potential applications in solvent-diffusion-driven crystallization and nucleation studies.