Breath Figure Assembly on Evaporating Polymer Solution Droplets in Levitation

Phys Rev Lett. 2023 Nov 24;131(21):218101. doi: 10.1103/PhysRevLett.131.218101.

Abstract

We investigate the drying of isolated polymer solution droplets, employing acoustic levitation, and demonstrate the spontaneous generation of breath figures (BF) on the resulting polymer particles and capsules (∼5-1000 μm) with controlled surface pore arrays (<1-20 μm). By contrast with supported polymer thin films, the evaporative cooling experienced by suspended droplets suffices to yield ubiquitous BF formation, owing to their thermal insulation and the synchronous condensation and self-assembly of water microdroplets, accompanied by capsule skin formation and kinetic arrest. A simple model describes simultaneously the radius and temperature evolution along the droplet-to-particle transformation, and the scaling of surface pore dimensions, with environmental parameters. The generality of the approach is demonstrated with a range of model polymers, and the coupled roles of solution thermodynamics and droplet environment are shown to permit the facile design of capsules with tunable transport and dissolution kinetics.