Browsing by Author "Muza, Upenyu Lucky"
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- ItemMulti-detector thermal field-flow fractionation (ThFFF) as a characterization technique for complex polymer self-assemblies(Stellenbosch : Stellenbosch University, 2017-03) Muza, Upenyu Lucky; Pasch, Harald; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Amphiphilic block copolymer micelles have found a niche in pharmaceutical, electronics, environmental, cosmetics and hygiene industries. These micelles, whether in the pure or mixed micelle form, often exist as multiple morphologies (spherical, cylindrical, worm or vesicular) in equilibrium with each other. However none of the current techniques can successfully separate and characterize these multiple morphologies with regards to size, molar mass, chemical composition and their respective distributions, in a single measurement. Thermal field-flow fractionation (ThFFF) is shown to be capable of separating and characterizing pure micelles prepared from two types of polystyrene - polyethylene oxide block copolymers (PS-PEO), of different PS block sizes but similar PEO block sizes. Moreover, multiple micelle morphologies induced by the addition of 1 mM LiBr, as well as multiple mixed micelles prepared from various binary blending protocols of the two PS-b-PEO copolymers were successfully characterized. In addition, ThFFF is shown to be capable of monitoring the dynamics of formation of the mixed micelles.
- ItemThermal field-flow fractionation and the advanced analysis of complex polymers(Stellenbosch : Stellenbosch University, 2019-12) Muza, Upenyu Lucky; Pasch, Harald; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Self-assemblies (SAs) and composites designed from block copolymers (BCPs) have found an important niche in nanotechnology. In order to establish commercially viable and sustainable polymeric applications for such materials in industry, there is a need to develop advanced analytical methods for their characterization. SAs being polymeric in nature inherently exhibit molecular heterogeneity, and thus their molecular properties are not specific but rather exist as distributions, which immensely impact on their ultimate performance. As such, there is a critical need to move away from the traditional batch mode analytical techniques which only yield average property values. Instead, it is imperative to embrace separation techniques such as size exclusion chromatography (SEC) and field-flow fractionation (FFF) which have been applied for the analysis of molecular properties and the corresponding distributions. In particular, the advent of thermal field-flow fractionation (ThFFF) as a sub-technique of FFF has enabled unique separations of SAs according to both hydrodynamic size (Dh) and chemical composition (CC). Herein, the focus of the research was directed at developing multidimensional analytical techniques for the analysis of SAs in three separate but mutually related studies. In the first case, the focus was on investigating the impact of microstructural and molecular packing differences of the core domains on the behaviour of SAs. The core microstructure and molecular density are cumulatively shown to impact on the morphology, critical micelle concentration (CMC), hydrodynamic diameter (Dh), molar mass (Mw), aggregation number (Z), elastic behaviour and thermal stability. Secondly, ThFFF was successfully applied in the analysis of nanoreactors. Specific SAs are shown to be capable of functioning as micelle nanoreactors (MNRs) by triggering phase separated and thermally induced physical transitions within the micelle core to produce new SAs with unique properties. In essence, the MNRs are shown to circumvent the inherent precipitations associated with stereocomplexation (SC) of polymers, thus providing a vital route for studying SCs in solution. Finally, a ThFFF-quintuple detection system (ThFFF-QD) was presented for the comprehensive analysis of SAs and other complex polymers. This novel approach used the so-called triple detection (TD), that is, differential viscometer (dVis), refractive index and (dRI) and static light scattering (SLS) detectors. TD was complimented by a second concentration detector (ultraviolet, UV) and a dynamic light scattering (DLS) detector. The method development process for ThFF-QD was based on linear, branched and isotopic polystyrenes (PSs) as model compounds. In particular, ThFFF of isotopic polystyrene analogues was fundamentally shown to exhibit gravimetric and density sensitivities. Structural information for SAs was elucidated from the Mark-Houwink (MH) and confirmation plots and correlated with chemical composition, structure, compactness, molar mass, aggregation number (Z), size and intrinsic viscosity (IV).