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Revista mexicana de ingeniería química

Print version ISSN 1665-2738


ORTIZ-ESTRADA, C. H. et al. Phase transition and stability of polymers solutions in supercritical CO2 by turbidimetry. Rev. Mex. Ing. Quím [online]. 2007, vol.6, n.3, pp.301-308. ISSN 1665-2738.

The phase behavior of polymer solutions in supercritical CO2 is a fundamental problem in particle formation process during the nucleation in solution, where the CO2 is either used like as solvent or antisolvent. In this work, it was determined by turbidimetry, the phase transition and stability by cloud point measurements. Particle size was monitored during the pressure induced phase separation from a homogeneous solution in cases where the CO2 is solvent (binary system) or antisolvent (ternary system). The studied systems were poly(fluorooctyl methyacrylate) (PFOMA)-CO2 and polystyrene (PS)-tetrahydrofuran (THF)-CO2, for different polymer concentrations, temperatures and pressures in the supercritical region of CO2. The results indicate that the system PFOMA-CO2 exhibits an LCST and for PS-THF-CO2 a combination of UCST-LCST phase behaviours are observed that is highly dependent on the THF-to-CO2 concentration ratio. By monitoring particle size in solution the transition stages and phase stability of stable-metastable-unstable states, which are associated with the spinodal region, are determined. The nucleation phenomenon appears once the solution crosses the spinodal curve toward the unstable area. In this region, the growth of the particles is exponential favouring coagulation that ultimately induces supersaturation.

Keywords : phase stability; polymers solution; turbidimetry; supercritical carbon dioxide.

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