Development of Continuous Two-Dimensional Thermal Field-Flow Fractionation for Polymers : Academic Dissertation

This research work was focused on the development of instrumentation, operations, and approximate theory of a new continuous two-dimensional thermal field-flow fractionation (2D-ThFFF) technique for the separation and collection of macromolecules and particles. The separation occur in a thin disk-shaped channel, where a carrier liquid flows radially from the center towards the perimeter of the channel, and a steady stream of the sample solution is introduced continuously at a second inlet close to the center of the channel. Under influence of the thermal field, the sample components are separated in radial direction according to the analytical ThFFF principle. Simultaneously, the lower channel wall is rotating with respect to the stationary upper wall, while a shear-driven flow profile deflects the separated sample components into continuous trajectories that strike off at different angles over the 2D surface. Finally, the sample components are collected at the outer rim of the channel, and the sample concentrations in each fraction are determined with the analytical ThFFF. The samples were polystyrene polymer standards and the carrier solvents cyclohexane and cyclohexane-ethylbenzene mixture in continuous 2D-ThFFF and tetrahydrofuran in analytical ThFFF. The thermal field had a positive effect on the sample deflection, although broadening of the sample zone was observed. Decreasing the channel thickness and the radial and angular flow rates of the carrier caused significant narrowing of the zone broadening. Systematic variation of the experimental parameters allowed determination of the conditions required for the continuous fractionation of polystyrene polymers according to their molar mass. As an example, almost baseline separation was achieved with two polystyrene samples of different molar masses. Meanwhile, an approximate theoretical model was developed for prediction of the trajectory of the sample component zone and its angular displacement under various operating conditions. The trends in the deflection angles without and with a thermal gradient were qualitatively in agreement with predictions of the model, but significant quantitative differences were found between the theoretical predictions and experimental results. The reasons for discrepancies between theory and experiment could be the following: relaxation of the sample already at the sample inlet, effect of solvent partition when binary solvent is used as the carrier, dispersion of the sample, limitations of the instrument, and geometrical imperfections. Despite its incompleteness, the theoretical model will provide guidelines for future interpretation and optimization of separations by continuous 2D-ThFFF method.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2014

Author dc:creator

• Vastamäki, Pertti

• analyyttinen kemia

Statement dc:rights

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Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/44959

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F44959