Abstract
M.Sc.
This report illustrates the synthesis and characterization of CdS and CdSe nanoparticles in TOPO, HDA and hexamethylenediamine. The prepared nanoparticles were characterized using UV-visible and photoluminescence spectrophotometers for optical properties, transmission electron microscopy for shapes and sizes as well as powder X-ray diffractometer for structural analysis. The effect of monomer concentration and temperature were investigated on the growth of nanocrystals. The monomer concentration was varied by changing the amount of stabilizer. The particle sizes increased with an increase in monomer concentration. Higher monomer concentration resulted in polydispersed nanoparticles due to faster uncontrolled growth. Increasing the temperature resulted in a faster growth thus increasing the size of the particles. The growth also affected the shapes of the particles as the particles tend to grow anisotropical ly at higher monomer concentration and high temperatures. The formation of tretrapods at high temperatures was due to a kinetically driven reaction as a result of increased temperature.
Hexamethylenediamine was found to be a poor capping agent for the prepared CdS nanoparticles. The particles prepared in the compound agglomerated at all temperatures used in preparation. Such results were associated with lower steric hindrance due to a shorter molecular chain.
The polymer nanofibres were fabricated via electrospinning technique while varying the concentrations of the polymer solutions. Solutions of low viscosity gave beaded fibres as mixtures of droplets and fibres due to the collection of wet fibres. An increase in the concentration (viscosity) of the solutions resulted in the deposition of solid fibres with bigger diameters. The TGA results show that PMMA electrospun fibres demonstrate a significant increase in thermal stability compared to the powder polymer. However the changes were very minimal on the PEO fibres.
CdS and CdSe nanoparticles were incorporated into PMMA and PEO and electrospun to fabricate composite fibres. The incorporation of the quantum dots caused an increase in the viscosity of the solutions and resulted in the collection of fibres with spiral morphology. However this increase of concentration caused an increase in the diameters of the composite fibres as evaluated from the SEM analysis. The EDS analysis showed the presence of Cd, S, and Se elements in the composite fibres due to the presence of CdS and CdSe. The XRD analysis of the composite showed no effect of the quantum dots on the amorphous peak of the PMMA. However on the PEO it showed a decrease in the intensity as the peaks as they become broader due to the decrease of crystallinty. The FTIR spectra showed that the presence of the quantum dots in the polymers on both PMMA and PEO. The optical analysis showed absorption and emissions peaks on the composites fibres due to the showed incorporated light emitter. These peaks were not affected by any change in the concentrations as a result of increased wt % of the quantum dots. Thermal analysis of the composite fibres demonstrates an increase in the thermal stability of the polymers after the incorporation of the quantum dots. Very small changes were observed for the quantum dots doped-PEO material compared to the doped PMMA. DSC analysis showed an increase in the glass transition temperature of the PMMA with increasing wt % of the CdS and CdSe. The addition of CdS and CdSe nanoparticles into PEO caused a decrease in the melting temperature of the polymer due to a decrease in the polymer crystallinity.