Abstract

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.