Calculation of ternary polymer solution phase diagram via compressible lattice fluid model extended to specific interactions

Risultato della ricerca: Other contribution

Abstract

Ternary polymer solutions are currently employed for the production of porous structures (e.g.membranes and scaffolds for tissue engineering) via liquid-liquid phase separation techniques. Therelation between processing conditions and thermodynamic features of the considered polymericsystem determines the morphology of the as-prepared membrane. Therefore, in order to achieve abetter control on a porous structure, a deep characterization of the phase behavior of a polymersolution is needed.The experimental derivation of phase diagrams is highly cost and time consuming, thus usuallythe cloud point curves of the system are directly measured. In this work, the compressible latticefluid extended to specific interactions was applied on a ternary polymer solution for the derivationof a complete phase diagram, where the cloud point data were employed for fitting the modelparameters.The investigation was focused on the poly-L-lactide (PLLA)-dioxane-water system, as it hasbeen employed for the preparation of both microfiltration membranes and scaffolds for tissueengineering purposes. Although the wide and growing scientific interest upon this system (and, ingeneral, on polymer-solvent-nonsolvent systems), a complete phase diagram of the system is notavailable in literature.The main feature of the considered model is the possibility to take into account for specificinteractions between the species, thus improving the system description. The original formulationwas derived and checked for a binary system: in this case, the applicability is tested on a ternarysystem. Hansen solubility parameters were scrutinized to select the appropriate interactionparameters to be taken into account: the total number of fitting parameters used was reduced tothree, upon six available, by considering specific interactions between the PLLA-dioxane pair andnonspecific interactions for the PLLA-water pair. The adjustable parameters were fitted on the basisof experimental cloud point data. The binodal curves were calculated by equating the chemicalpotentials of species in the separated phases, and by solving the system with the equation of statefor each phase. The cloud points were determined by the intersection of the binodal curve with astraight line corresponding to a fixed solvent/nonsolvent proportion. The model is able to reproducequalitatively and quantitatively the cloud point curves of the system. The as-obtained interactionparameters were used to calculate a complete phase diagram of the system. Thus, from simpleexperimental data, as cloud point curves are, a more complex information was derived.In principle, the proposed method can be employed for the derivation of the phase diagrams ofsimilar systems, thus improving the information supporting the microstructure control of polymericfoams.
Lingua originaleEnglish
Numero di pagine1
Stato di pubblicazionePublished - 2012

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