Breath Figure Assembly on Evaporating Polymer Solution Droplets in Levitation

Area of Science:

• Materials Science
• Physical Chemistry
• Fluid Dynamics

Background:

• Drying of polymer solutions can lead to porous structures.
• Breath figures (BF) are typically formed on supported thin films.
• Controlling pore formation in levitated droplets is challenging.

Purpose of the Study:

• To investigate the spontaneous generation of breath figures on isolated polymer solution droplets during drying.
• To demonstrate the formation of controlled surface pore arrays on polymer particles and capsules.
• To establish a model for droplet transformation and pore dimension scaling.

Main Methods:

• Acoustic levitation of isolated polymer solution droplets.
• Controlled drying and evaporative cooling of levitated droplets.
• Characterization of resulting polymer particles and capsules, including surface pore arrays.

Main Results:

• Ubiquitous breath figure formation on suspended droplets due to evaporative cooling and thermal insulation.
• Synchronous condensation and self-assembly of water microdroplets leading to pore formation.
• Successful fabrication of polymer particles and capsules (5-1000 μm) with tunable pore sizes (<1-20 μm).
• A simple model accurately describes droplet evolution and pore scaling with environmental parameters.

Conclusions:

• Evaporative cooling of levitated droplets is sufficient for breath figure formation, unlike supported films.
• The approach allows facile design of capsules with tunable transport and dissolution kinetics.
• This method offers a versatile platform for creating functional porous polymer materials.