Controlling Profiles of Polymer Dots by Switching between Evaporation and Condensation

We found that the profiles of the dots formed from the drying droplets of polymer solution can be modified by switching between the evaporation and condensation processes. When a polymer dot is exposed to solvent vapor during a certain time and is dried again, the dot profile changes from ringlike to flat. To obtain a flat dot, there exists an optimal exposure time. We conjecture that the change of the dot profile is due to the refluidization of the polymer film. Our results imply a new possibility for controlling the dot profile in inkjet printing technologies.