Browsing by Author "Hurme, Markku, Professor"

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Investigation of critical parameters of an emulsion-solvent extraction based microsphere preparation process
(2012) Heiskanen, Harri
School of Chemical Technology | Doctoral dissertation (article-based)
The aim of this PhD thesis was to develop further the novel hydrocarbon-in-fluorocarbon emulsion solvent extraction based microsphere preparation process. In the first step of the process an emulsion was produced. The dispersed phase of the emulsion contained the matrix material of the microspheres. In the second step of the process, the hydrocarbon from the dispersed phase was extracted into the continuous phase by mixing the emulsion with the excess of the perfluorocarbon. Two different solidification strategies were used: I) the emulsion formed in a vessel was transferred into another vessel containing an excess of the perfluorocarbon, and II) the excess of the perfluorocarbon was added to the emulsion. The critical emulsification and solidification parameters affecting the size, the size distribution, and the morphology of the microspheres were investigated. A good agreement between the size of the microspheres and the Weber number (emulsification step) was found. With the preparation method I, the mixing conditions in the solidification step also affected the size of the microspheres, partly because the stability of the hydrocarbon-in-perfluorocarbon emulsion was poor. The size of the microspheres was affected not only by the surfactant concentration but also by the volume ratio of the dispersed phase to the continuous phase. At a low volume ratio of the phases, the surfactant concentration was the dominating factor, whereas the volume ratio of the phases was the dominating factor at a high volume ratio. The viscosity of the phases affected the size of the microspheres. The viscosity of the dispersed phase decreased with a decreasing matrix material concentration and as a result, the size of the microspheres decreased. The size of the microspheres decreased as the continuous phase viscosity increased. The morphology of the microspheres could be controlled by changing the solidification rate. The solidification rate was adjusted by changing the temperature of the perfluorocarbon used in the solidification step and the hydrocarbon concentration of the perfluorocarbon used in the solidification step. The compactness of the microspheres increased with a decreasing solidification rate.