Experimental and Theoretical Investigation of an Aqueous Two Phase System with a Hyperbranched Polymer

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Extraction which is based on the miscibility gap of aqueous two phase systems (ATPS) is a principal possibility to concentrate proteins. These systems are composed by adequate polymers, salts. The fundamental idea of this research project was the extension of the material base by the application of hyperbranched polyesteramid in combination with dextran to form an ATPS. The characteristics of this ATPS were compared with a classical ATPS composed of PEG8000 and dextran. In contrast to linear polymers hyperbranched polymers with different functional groups and different architectures which influence the thermodynamic behaviour and the miscibility gap can be synthesized. A further advantage of hyperbranched polymers in fluid separation is the low viscosity compared to linear polymers. In both ATPS the partitioning of L-serin on the two coexisting phases was experimentally investigated. The modeling of the phase equilibria which are the basis of the extraction can be realized by a thermodynamic model which accomplishes for the polymer architecture and the functional groups of the hyperbranched polymer. The thermodynamic model is the Lattice Cluster theory (LCT) combined with the Wertheim Theory. By the application of the developed thermodynamic model it was possible to predict the partitioning of L-serin on the phases of both ATPS by an adjustment of the model parameters to binary respectively ternary subsystems. As a subsequent step, the developed thermodynamic model will be used to investigate interfacial phenomena of both ATPS such as interfacial tension or mass transfer across the interface. The modelling of these phenomena will be conducted by the combination of the developed model with the density gradient theory (DGT). The DGT gives an expression for the Helmholtz Energy of an inhomogeneous system. Therefore, it is possible to calculate the interfacial tension in equilibrium and to provide an expression for the chemical potential which allows calculating the mass transfer. In addition to the modelling the interfacial tension and the mass transfer across the interface will be experimentally determined. For this investigation, the spinning drop method will be used to determine the interfacial tension and a Nitsch-celle will be used to investigate the mass transfer across the interface. If this project is successful, a closed theory for the description of ATPS including phase equilibria and mass transfer would be provided in addition to the considerably extension of the material base of ATPS.