Nonsolvent-Induced Solidification of Droplets of a Polymer Solution: From a Sphere to a Capsule

Droplets of a polymer solution can solidify in a nonsolvent bath, forming solid capsules and particles. However, the dynamics of this process, based on nonsolvent-induced phase separation, remains elusive. In this work, the solidification dynamics of polymer solution droplets is explored using dissipative particle dynamics simulations for different initial polymer concentrations. The dynamics of the shrinking droplets is monitored. Additionally, the evolutions of solvent and nonsolvent concentrations are examined, and the local polymer concentration profiles are analyzed. Furthermore, the microstructural characteristics of polymers, including the degree of crystallinity (local alignment) and the radius of gyration of polymers, are investigated. It is interesting to observe that the macroscopic morphology and microscopic configuration are significantly dependent on initial polymer concentrations. At higher concentrations, hollow particles are formed, containing polymer shells with longer persistence lengths. Conversely, lower concentrations lead to the creation of solid particles with increased chain-folding. Our results provide valuable insights into the influence of initial polymer concentrations on polymeric capsules and particle formation.