Accession Number : ADA299490

Title :   Particle Formation During the Expansion of Supercritical Solutions.

Descriptive Note : Annual technical rept. 1 Aug 93-31 Jul 94,

Corporate Author : PRINCETON UNIV NJ DEPT OF CHEMICAL ENGINEERING

Personal Author(s) : Debenedetti, Pablo G.

PDF Url : ADA299490

Report Date : 31 AUG 1994

Pagination or Media Count : 41

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.

Descriptors :   *POLYMERS, *PARTICLES, *SUPERCRITICAL FLOW, *EXPANSION, *LACTIC ACID, DENSITY, FLUORESCENCE, MODELS, SILICON DIOXIDE, ONE DIMENSIONAL, MORPHOLOGY, MIXTURES, MICROSCOPY, TRANSMITTANCE, PRECIPITATION, FLUORINE, FLUIDS, CALIBRATION, METHANE, CARBON DIOXIDE, EXITS, ASPECT RATIO, DENDRITIC STRUCTURE, CHLORINE, ORIFICES, MICROSPHERES.

Subject Categories : Inorganic Chemistry
      Organic Chemistry
      Physical Chemistry
      Polymer Chemistry
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE