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Title: Polymer solution themodynamics
Author: Garcia Sakai, Victoria
ISNI:       0000 0004 2743 3092
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2002
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In this work, the validity of two thermodynamic models, the Sanchez-Lacombe equation of state [SL EoS] and the UNIFAC-free volume [UNIFAC-FV] activity coefficient model, in predicting the phase behaviour of polymer solutions, was analysed. For this, liquid-liquid and vapour-liquid equilibrium data were measured for polystyrene [PS] and poly(methyl methacrylate) [PMMA], in solution with a common solvent, cyclohexanol. A block and a random copolymer were also investigated in this solvent. Cloud-point curves [CPC] were measured by thermo-optical analysis using a turbidimeter, which was constructed to measure, as a function of temperature and composition, changes in transmitted light intensity through the aforementioned solutions. Measurements were carried out in solutions containing up to —25% polymer by weight, in the temperature range 290-523K and at the solvent vapour pressure. Solvent activity coefficients were measured in the temperature range 383.15-493.15K using inverse gas chromatography. Data was collected at infinite dilution and at finite concentrations of solvent (up to —30% by weight), the latter using the elution on a plateau technique. The SL EoS correctly predicted the observed UCST behaviour in all systems and the molecular weight dependence of the CPCs. Quantitative agreement of the critical temperatures was achieved by fitting the binary interaction parameter [k12]; however it was not possible to simultaneously fit the critical compositions. In contrast, UNIFAC-FV fails to predict a phase-split in the PMMA or copolymer solutions and over-predicts the UCST of the PS system. Despite this, UNIFAC-FV is superior in predicting the observed decrease in solvent activity coefficients as a function of increasing temperature and solvent concentration. Finally, an enhanced solubility with respect to its homopolymers, is observed in the random copolymer, owing to increased molecular interactions. This cannot be predicted by either model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available