Abstract
Controlled homogeneous nucleation and crystal growth were examined as a means of controlling the morphology of particles obtained from the drying of solution droplets. Crystallization was expected to initiate at the surface of the solution droplet because of the concentration of the solute there. Consequently, the size of the droplet at the onset of crystallization might be important in determining the particle size if a shell was formed. However, using classical homogeneous nucleation theory, this crystallization size was found to be relatively unaffected by different parameters except for the mass of solute where lower density particles were found to be more probable for higher solute mass. The morphology of a particle is determined by the number of crystals formed, their habit and arrangement. Hence, the parameters that affect the activation of nuclei and crystal growth will control the morphology. These parameters include the temperature, evaporation rate of the solvent, crystal habit, solubility and mass of the solute. Given a solute, limited control of the morphology of the particle produced should be achievable through the temperature and vapor pressure (humidity) of the carrier gas. Although density and shape may be controllable, the aspect ratio of particles produced is not expected to be large because of the sphericity of the droplets.
Published Version
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