Particle Formation During the Expansion of Supercritical Solutions.
Abstract
An experimental study of poly (L-lactic acid ) (L-PLA) precipitation by rapid expansion of supercritical solutions in silica capillaries was carried out. The solvent was a mixture of carbon dioxide and chlorodifluoromethane. Three particle morphologies were observed: dendrites, microspheres, and irregular polyhedra (microparticles). Dendrites formed only with calibrated orifices (aspect ratio, L/D < 10). In capillaries, microspheres were always formed if the carrier fluid's density at the capillary's exit exceeded 0.0063 mol/cu cm; microparticles were always formed if the carrier fluid's exit density was lower than 0.0042 mol/cu cm (densities were calculated with a one-dimensional model of adiabatic choked flow, in conjunction with the Peng-Robinson equation of state). Microparticles formed primarily inside the silica capillary; microspheres, in the free jet after exiting the capillary. In a second study, fluorescence and transmission microscopy were used to study the distribution of pyrene (fluorescent) in L-PLA (non-fluorescent) microspheres obtained by co-precipitation from a rapidly expanding supercritical carrier. Uniform distribution of pyrene inside the polymer microspheres was achieved.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 31, 1994
- Accession Number
- ADA299490
Entities
People
- Pablo G. Debenedetti
Organizations
- Princeton University