(252e) Laser Induced Fluorescence Studies of Solute Concentration In the Supercritical Antisolvent Precipitation Process

Spray visualization studies of the super critical antisolvent (SAS) process for poly methyl methacrylate (PMMA) and other polymers has shown that wide variations in operating conditions produce sprays with drastically different characteristics, yet particles that result from the sprays differ little in size and size distribution.  Certain operating conditions do produce distinct particle size distributions, but there appears to be little relation to measured spray characteristics such as jet break-up length and drop size.  Key to understanding the particle precipitation is to determine where within the spray the particle nucleation and growth occurs.  To this end, we have employed planar laser induced fluorescence (PLIF) studies within the SAS precipitation process using a fluorescent molecule, poly[methylmethacrylate-co-(7-(4-trifluoromethyl)coumarin methacrylamide)], as the solute in a solvent acetone with compressed carbon dioxide as the antisolvent.  The molecule fluoresces when illuminated with a planar sheet of laser light (from a nitrogen laser) and the intensity of fluorescence is recorded at high spatial resolution with a back-illuminated CCD camera and at high magnification with a special distance microscope lens.  The visualizations reveal regions of high concentration of the solute within the spray.  The spray characteristics and fluorescence fields were determined for several process conditions by visualizing the spray at various distances from the nozzle outlet. The precipitated particles from these studies were collected and analyzed with a scanning electron microscope and a particle size distribution analysis was performed. The relationship between the concentration measurements in the SAS spray and the particle sizes will be discussed.