Size Determination of Ultra Fine Particles and Molecular Assembly in Supercritical Fluids

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Photon correlation spectruscopy (PCS) is one of the poweful in situ techniques to determine size of fine particles of nanometer order within a few second analysis time. We tried the size measurement of particles dispersed in high pressure liquid and supercritical fluid by using PCS.1. PCS was made, which had the pressure-resistant cylindrical light scattering cell with a high precision sapphire tube. It was found that an injector with a 5muL sampleloop could be used to injectparticles suspended in methanol, as usual way of a conventional liquid chromatography.2. The effect of pressure on the size measurement was carried out, with the purpose of the leak test for the pressure-resistant. Colloidal silica particles with a narrow size distribution in methanlo were measured under up to 30 MPa at 298K.The observed particle diameter agreed with the size measured at an atmospheric pressure. This fact indicates PCS could be used as the size measurement of sub-micron particles dispersed in high … More pressure and high dense phase.3. When polystirene latex particles in methanol were used, the particle size increased to 1.2 times larger than the nominal diameters during the pressure increased only up to 1 MPa, and then was almost constant under the pressure ranges from 2 to 30 MPa. It might be concluded that polystirene polymer could swell with methanol at the relatively low pressure.4. The results of the size measurement of polystirene latex particles in supercritical carbon dioxide at 20 MPa and 313 K indicated that the observed particle diameters increase with time and the calculated polydispersed indexes also become large. We concluded the polystirene latex particles agglomerated quickly, but could not determined the effects of methanol in supercritical carbon dioxide on the particle agglomeration, which was used as the solution at the sample preparation.5. The viscosity of the binary mixure of methanol and carbon dioxide at 20 MPa and 313 K estimated by Lobe's method was fairly agree with the viscosity calculated from PCS measurements in the mixture solvent and from particle size assuming same value as in pure methanol, at the region of less carbon dioxide content than 60 volume %.6. From this study, the viscosity of the pure or mixture solvent can be measured by PCS with uniform particles known size. However, the crucial aspect of this measuring method is the selection of suitable particles for a probe which form a stable suspension in the solvent to know the viscosity. Less