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| - SANS Study of Polymer−Supercritical Fluid Solutions: Transitionsfrom Liquid to Supercritical Fluid Solvent Quality
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| - Phase behavior and small-angle neutron scattering (SANS) measurements are reportedfor poly(ethylene-co-1-butene) (PEB) dissolved in pentane, pentane plus ethane, and supercritical ethaneto pressures of 2000 bar and temperatures of 130 and 150 °C. The solution microstructure and solventquality are probed using the high-concentration isotopic labeling technique at the mixture criticalconcentration to determine the variation of intra- and intermolecular correlations on approach to thephase boundary with isothermal changes in pressure. The SANS results for the three solutions showthat the intramolecular radius of gyration remains close to the unperturbed value over the entire pressurerange investigated. However, the intermolecular correlation length changes dramatically as the phaseboundary is approached and is approximately 3 times larger in ethane as compared to pentane even at1000 bar from the phase boundary. The intermolecular correlation length data suggest that ethane is apoorer quality solvent than pentane at conditions close to the phase boundary even though both solventshave similar mass densities.
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