Transición y estabilidad de fase de soluciones poliméricas en CO₂ supercrítico por turbidimetría

Phase transition and stability of polymers solutions in supercritical CO₂ by turbidimetry

C. H. Ortiz–Estrada¹*, J. G. Santoyo–Arreola¹, G. Luna–Bárcenas², I. C. Sanchez³ y R. C. Vásquez–Medrano¹

¹ Departamento de Ingeniería y Ciencias Químicas, Universidad Iberoamericana, Prolongación Paseo de la Reforma #880, Lomas de Santa Fe, México, D. F. 01219 México. * Autor para la correspondencia: E–mail: ciro.ortiz@uia.mx Tel. (55)–59504074. Fax. (55)–59504279

² Laboratorio de Investigación en Materiales, CINVESTAV Unidad Querétaro, Querétaro, Querétaro 76230 México.

Recibido 11 de Septiembre 2007
Aceptado 22 de Noviembre 2007

Resumen

El comportamiento de fase de una solución polimérica en CO₂ supercrítico es un problema fundamental en el proceso de formación de partículas durante la nucleación en solución, donde el CO₂ es utilizado ya sea como solvente o antisolvente. En este trabajo, se determinó mediante turbidimetría, la transición y estabilidad de fase aplicando la medición del punto de nube y el monitoreo del tamaño de partícula durante la separación de fase inducida por presión, a partir de una solución homogénea en casos donde el CO₂ es solvente (sistema binario) o antisolvente (sistema ternario). Los sistemas estudiados fueron: poli(fluoroctil metacrilato) (PFOMA)–CO₂ y poliestireno (PS)–Tetrahidrofurano (THF)–CO₂, para diferentes condiciones de concentración del polímero, temperatura y presión en la región supercrítica del CO₂. Los resultados indican que el sistema PFOMA–CO₂ presenta una comportamiento LCST común para polímeros fluorados solubles en CO₂; para PS–THF–CO₂ el comportamiento UCST–LCST son observados que son altamente dependientes de la relación de concentración THF/CO₂.

El monitoreo del tamaño de partícula en solución, muestra las etapas de transición y estabilidad de fase de estable–metaestable–inestable, observándose la región espinodal. El fenómeno de nucleación aparece de manera importante una vez que la solución cruza la curva espinodal hacia la zona inestable, donde el crecimiento de las partículas es exponencial favoreciendo por lo tanto el mecanismo de coagulación, inducido por la supersaturación de la solución.

Palabras clave: dióxido de carbono supercrítico, estabilidad de fase, soluciones poliméricas, turbidimetría.

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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Referencias

Andersson M.; Wittgren B. y Wahlund K.–G. (2003). Accuracy in multiangle light scattering measurements for molar mass and radius estimations. Model calculations and experiments. Analytic Chemistry 75, 4279-4291.         [ Links ]

Berger, T., Steffen, W. (2000). Optical flow–through high pressure cell for light scattering investigations. Review of Scientific Instruments 71, 2467–2470.         [ Links ]

Blasig, A., Shi, C., Enick, R.M., Thies, M.C. (2002). Effect of concentration and degree of saturation on RESS of a CO2–Soluble fluoropolymer. Industrial and Engineering Chemistry Research 41, 4976–4983.         [ Links ]

Bohren, C.F. y Huffman, D.R. (1983). Absorption and scattering of light by small particles, John Wiley & Sons, USA.         [ Links ]

Chernyak, Y.; Henon, F.; Harris, R.B.; Gould, R.D.; Franklin, R.K.; Edwards, J.R.; DeSimone, J.M., Carbonell, R.G. (2001). Formation of perfluoropolyether coatings by the rapid expansion of supercritical solutions (RESS) process. Part 1: Experimental results. Industrial and Engineering Chemistry Research 40, 6118–6126.         [ Links ]

Cooper, A.I. (2001). Developments in materials synthesis and processing using supercritical CO₂. Advanced Materials 13, 1111–1114.         [ Links ]

Crawley, G.; Cournil, M. y Di Benedetto, D. (1997). Size analysis of fine particle suspensions by spectral turbidimetry: potential and limits, Powder Technology 91, 197–208.         [ Links ]

Dao, L.H.; Nguyen, H.M. y Mai, H.H. (2000). A fiber optic turbidity system for in–situ monitoring protein aggregation, nucleation and crystallization. Acta Astronautica 47, 399-409.         [ Links ]

De Gennes, P.–G. (1979). Scaling concepts in polymer physics, Cornell University Press, USA.         [ Links ]

Debenedetti, P.G.; Tom, J.W.; Kwauk, X., Yeo, S.D. (1993). Rapid expansion of supercritical solutions (RESS): Fundamentals and applications. Fluid Phase Equilibria 82, 311-321.         [ Links ]

Dickson, J.L.; Ortiz–Estrada, C.; Alvarado, J.F.J.; Hwang, H.S.; Sanchez, I.C.; Luna–Bárcenas, G.; Lim, K.T., Johnston, K.P. (2004). Critical flocculation density of dilute water–in–CO2 emulsions stabilized with block copolymers. Journal of Colloid Interface Science 272, 444–456.         [ Links ]

Dickson, J.L.; Psathas, P.A.; Salinas, B.; Ortiz–Estrada, C.; Luna–Barcenas, G.; Hwang, H.S.; Lim, K.T., Johnston, K.P. (2003). Formation and growth of water–in–CO2 miniemulsions. Langmuir 19, 4895–4904.         [ Links ]

Elvassore, N.; Baggio, M.; Pallado, P.; Bertucco, A. (2001). Production of different morphologies of biocompatible polymeric materials by supercritical CO2 antisolvent techniques. Biotechnology and Bioengineering 73, 449-457.         [ Links ]

Fages, J.; Lochard, H.; Letourneau, J.–J.; Sauceau, M.; Rodier, E. (2004). Particle generation for pharmaceutical applications using supercritical fluid technology. Powder Technology 141, 219–226.         [ Links ]

Fehrenbacher, U., Ballauff, M. (2002). Kinetics of the early stage of dispersion polymerization in supercritical co2 as monitored by turbidimetry. 2. Particle formation and locus of polymerization. Macromolecules 35, 3653-3661.         [ Links ]

Frontini, G.L., Elicabe, G.E. (2000). A novel methodology to estimate the particle size distribution of latex using relative measurements of elastic light scattering and turbidimetry. Journal of Chemometrics 14, 51–61.         [ Links ]

Gupta, R.B. (2006). Supercritical fluid technology for particle engineering. Drugs and the Pharmaceutical Sciences 159, 53–84.         [ Links ]

Harrison, K.L.; da Rocha, S.R.P.; Yates, M.Z.; Johnston, K.P.; Canelas, D., DeSimone, J.M. (1998). Interfacial activity of polymeric surfactants at the polystyrene–carbon dioxide interface. Langmuir 14, 6855–6863        [ Links ]

Jarmer, D.J.; Lengsfeld, C.S. y Randolph, T.W. (2004). Nucleation and growth rates of poly(L–lactic acid) microparticles during precipitation with a compressed–fluid antisolvent. Langmuir 20, 7254–7264.         [ Links ]

Jinbo, Y.; Teranuma, O.; Kanao, M.; Sato, T., Teramoto, A. (2003). Light–scattering study of semiflexible polymer solutions. 4. n–Hexane solutions of poly(n–hexyl isocyanate). Macromolecules 36, 198–203.         [ Links ]

Jung, J., Perrut, M. (2001). Particle design using supercritical fluids: Literature and patent survey. Journal of Supercritical Fluids 20, 179–219.         [ Links ]

Kanao, M.; Matsuda, Y., Sato, T. (2003). Characterization of polymer solutions containing a small amount of aggregates by static and dynamic light scattering. Macromolecules 36, 2093–2102.         [ Links ]

Kerker, M. (1969). The scattering of light and other electromagnetic radiation, Academic Press, USA.         [ Links ]

Lengsfeld, C.S.; Delplanque V.H.; Barocas, V.H., Randolph, T.W. (2000). Mechanism governing microparticle morphology during precipitation by a compressed antisolvent: atomization vs nucleation and growth. Journal of Physical Chemistry B 104, 2725–2735.         [ Links ]

Lim, K.T.; Lee, M.Y.; Moon, M.J.; Lee, G.D.; Hong, S.–S.; Dickson, J.L., Johnston, K.P. (2002). Synthesis and properties of semifluorinated block copolymers containing poly(ethylene oxide) and poly(fluorooctyl methacrylates) via atom transfer radical polymerization. Polymer 43, 7043–7049.         [ Links ]

Liu, K., Kiran, E. (1999). Kinetics of pressure–induced phase separation (PIPS) in solutions of polydimethylsiloxane in supercritical carbon dioxide: crossover from nucleation and growth to spinodal decomposition mechanism, Journal of Supercritical Fluids 16, 59–79.         [ Links ]

Luna–Bárcenas, G.; Mawson, S.; Takishima, S.; DeSimone, J.M.; Sanchez, I.C., Johnston, K.P. (1998). Phase behavior of poly(l,l–dihydroperfluorooctylacrylate) in supercritical carbon dioxide. Fluid Phase Equilibria 146, 325–337.         [ Links ]

Matsuyama, K.; Mishima, K.; Hayashi, K.–I.; Ishikawa, H.; Matsuyama, H. y Harada, T. (2003). Formation of microcapsules of medicines by the rapid expansion of a supercritical solution with a nonsolvent. Journal of Applied Polymer Science 89, 742-752.         [ Links ]

Mawson, S.; Johnston, K.P.; Combes, J.R. y DeSimone, J.M. (1995). Formation of poly(1,1,2,2–tetrahydroperfluorodecylacrylate) submicron fibers and particles from supercritical carbon dioxide solutions. Macromolecules 28, 3182–3191.         [ Links ]

Morita, S.; Tsunomori, F., Ushiki, H. (2002). Polymer chain conformation in the phase separation process of a binary liquid mixture. European Polymer Journal 38, 1863–1870.         [ Links ]

O'Neill, M.L.; Yates, M.Z.; Johnston, K.P.; Smith, C.D., Wilkinson, S.P. (1998a). Dispersion polymerization in supercritical CO2 with siloxane–based macromonomer. 2. The particle formation regime Macromolecules 31, 2848–2856.         [ Links ]

O'Neill, M.L.; Yates, M.Z.; Johnston, K.P.; Smith, C.D. y Wilkinson, S.P. (1998b). Dispersion polymerization in supercritical CO2 with a siloxane–based macromonomer: 1. The particle growth regime. Macromolecules 31, 2838–2847.         [ Links ]

O'Neill, M.L.; Yates., M.Z.; Harrision, K.L.; Johnston, K.P.; Canelas, D. A.;Betts, E.E.; DeSimone, J.M. y Wilkinson, S.P. (1997). Emulsion stabilization and flocculation in CO2. 1. turbidimetry and tensiometry. Macromolecules 30, 5050–5059.         [ Links ]

Perrut, M. (2000). Supercritical fluid applications: industrial developments and economic issues, Industrial and Engineering Chemistry Research 39, 4531–4535.         [ Links ]

Reverchon, E. y Adami, R. (2006). Nanomaterials and supercritical fluids. Journal of Supercritical Fluids 37, 1–22.         [ Links ]

Ritzl, A.; Belkoura, L., Woermann, D. (1999). Static and dynamic light scattering experiments on semidilute solutions of polystyrene in cyclohexane between the 9–temperature and the binodal curve. Physical Chemistry Chemical Physics 1, 1947–1955.         [ Links ]

Shekunov, B.Y.; Baldyga, J.; York, P. (2001). Particle formation by mixing with supercritical antisolvent at high Reynolds numbers. Chemical Engineering Science 56, 2421–2433.         [ Links ]

Teraoka, I. (2002). Polymer Solutions. An Introduction to Physical Properties, John Wiley & Sons, USA.         [ Links ]

Tomasko, D.L.; Li, H.; Liu, D.; Han, X.; Wingert, M.J.; Lee, L.J., Koelling, K.W. (2003). A review of CO₂ applications in the processing of polymers. Industrial and Engineering Chemistry Research 42, 6431–6456.         [ Links ]

Weber, M.; Russel, L.M., Debenedetti, P.G. (2002). Mathematical modeling of nucleation and growth of particles formed by the rapid expansion of a supercritical solution under subsonic conditions. Journal of Supercritical Fluids 23, 65–80.         [ Links ]

Xiong, Y., Kiran, E. (2000). Kinetics of pressure–induced phase separation (PIPS) in polystyrene + methylcyclohexane solutions at high pressure. Polymer 41, 3759–3777.         [ Links ]

Yates, M.Z.; Shah, P.S.; Johnston, K.P.; Lim, K.T., Webber, S. (2000). Steric stabilization of colloids by poly(dimethylsiloxane) in carbon dioxide. Effect of cosolvents. Journal of Colloid Interface Science 227, 176–184.         [ Links ]

Yeo, S.–D., Kiran, E., 2005, Formation of polymer particles with supercritical fluids: A review. Journal of Supercritical Fluids 34, 287–308.         [ Links ]

Zhuang, W., Kiran, E. (1998). Kinetics of pressure–induced phase separation (PIPS) from polymer solutions by time–resolved light scattering. Polyethylene + n–pentane. Polymer 39, 2903–2915.         [ Links ]