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Mode of access: World Wide Web. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 94-111). / Electronic reproduction. / Also available by subscription via World Wide Web / xv, 111 leaves, bound ill. (some col.) 29 cm

Two novel methods for the sulphur vulcanisation of NR, BR and EPDM rubbers using N-tert-butyl-2-benzothiazole sulphenamide (TBBS) accelerator and zinc oxide (ZnO) activator have been developed. In one method, the optimum loading of TBBS and ZnO were measured for some sulphur-filled NR, BR and EPDM rubbers. The cure systems for the NR were (S/TBBS/ZnO), (1/1.5/0.2), (2/1.5/0.3), (3/1.5/0.25), and (4/3.5/0.2), for the BR, (0.5/1.75/0.2) and (1/3/0.2), and for the EPDM, (1/1/0.075). The cure was very efficient in spite of reducing the amount of TBBS and ZnO chemicals. In another method which used a single additive component in the form of a powder (TBBS/ZnO: 350mg/1g), the loading of the powder in NR was raised increasingly from 0.63 to 5.63 phr, the scorch time was unchanged and the optimum cure time reduced at 1.25 phr powder. The rate of cure accelerated at 1.25 phr powder. The crosslink density reached its maximum value at 5.63 phr powder. This method reduced the TBBS and ZnO requirement in the cure system by 85wt%. Solid kaolin filler pre-treated with a sulphur-bearing mercaptosilane was used to reinforce NR, BR and EPDM rubbers. For NR, to react the sulphur in the silane on the kaolin surface with the rubber chains and optimise the reaction between the two, 16 phr TBBS and 0.2 phr ZnO were added to the kaolin-filled rubber. The hardness and Young s modulus increased and compression set decreased when up to 3 phr elemental sulphur was included in the kaolin-filled rubber with 16 phr TBBS and 0.2 phr ZnO. The tensile strength, elongation at break, stored energy density at break, and tear energy of the rubber vulcanisate reduced when elemental sulphur was added. Notably, the inclusion of elemental sulphur was the key factor in controlling the rubber properties. In an extended work, 60 phr silane pre-treated kaolin was mixed with NR, BR and EPDM and the rubbers were cured using the novel cure systems developed earlier. The effect of 140 phr kaolin on the properties of NR was also investigated. For NR, the hardness increased by 64% when 60 phr kaolin was added and the trend continued rising by another 28% when the loading of kaolin reached 140 phr. Similarly, the Young s modulus rose by 170% with 60 phr kaolin and then by an extra 148% when the full amount of kaolin, i.e. 140 phr, was reached. The tensile strength and tear energy were unchanged and the elongation at break and stored energy density at break deteriorated by a total of 65% and 34%, respectively with 140 phr kaolin. The compression set of the unfilled rubber was 41%, and it then rose to 64% and 71%, when 60 and 140 phr kaolin was added, respectively. For BR, the hardness increased by 23% and for EPDM, by 34%, respectively when 60 phr kaolin was incorporated in the rubbers. For BR, the tensile strength, elongation at break and Young s modulus rose by 759%, 256% and 114%, respectively. The compression set of the unfilled BR was 9.4%, and subsequently rose to 26% when 60 phr kaolin was mixed with the rubber. For EPDM, the tensile strength, elongation at break and Young s modulus improved by 964%, 332% and 71%, respectively. For BR, the stored energy density at break and tear energy were increased by 2442% and 536%, respectively and for EPDM, by 3133% and 1479%, respectively. The compression set of the unfilled EPDM was 39%, and afterward increased to 48% with 60 phr kaolin. Kaolin was found to be extending or non-reinforcing filler for the strain-induced crystallising NR and highly reinforcing for the non-crystallising BR and EPDM.

In recent years, portable devices and larger display are the trend of market, so transparent conducting oxides (TCO) draw a considerable interest due to their unique characteristics and essential role in the technology of flat panel display. Indium tin oxide (ITO) is one of the most widely used TCO in the application of display technology. In this work, properties of ITO thin film as a function of dopant ratio and density of sputtering targets had been done. It is found that the mechanism of oxygen vaccines is more dominated in electrical conduction than dopant concentration. Meanwhile, the conductivity of ITO thin film depends on the sputtering condition than the target itself. Annealing process is one of the ways to enhance the optical properties of ITO thin film. This process can change the crystal structure of film from amorphous to crystalline but limited by the presence of the oxygen. Apart from the transitional single layer of ITO thin film, a modified structure had been done by inserting a thin layer of metal (Al/Ag) into ITO which provides a highway for carrier transparent. A modified structure with Ag is successfully demonstrated and well agrees with the theory. OLED application was also done by using sandwich structure. The key of sandwich structure is the metal layer, non-reactive and highly conducting material should be selected. Upper and bottom TCO layers are purpose-built for application without affect the properties of structure. This structure also shows more robust on the flexible substrate than single layer ITO.

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This work describes, for the first time, the electrochemical and electrocatalytic properties of self-assembled layers of single-walled carbon nanotubes (SWCNTs) intergrated with selected organo-iron complexes and Cysteamine (Cys) forming a base on gold electrodes. The organo-iron complexes selected for this study were octa(hydroxyethylthio)phthalocyaninatoiron(II) (FeOHETPc), tetraaminophthalocyninatoiron(II) (FeTAPc), tetraaminophthalocyninatocobalt(II) (CoTAPc), ferrocene monocarboxylic acid (FMCA), ferrocene dicarboxylic acid (FDCA) or a mixture of SWCNT and FMCA or FDCA. The successful fabrication of these electrodes were established using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and electrochemical techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave voltammetry (SWV) and chronoamperometry (CA) The Au-Cys-SWCNT-FeOHETPc electrode exhibited strong dependence on the reaction of the head groups and the pH of the working electrolytes. The high electron transfer capability of the Au-Cys-SWCNT-FeOHETPc electrode over other electrodes as the Au-Cys-SWCNT or the Au-Cys-FeOHETPc or the Au-FeOHETPc suggests that SWCNT greatly improves the electronic communication between FeOHETPc and the bare gold electrode. The electron transfer rate constant (kapp) of Au-Cys-SWCNT-FeOHETPc in pH 4.8 conditions (~1.7 x 10-2 cm s-1) over that of the electrode obtained from SWCNT integrated with tetraaminophthalocyninatocobalt(II) (Au-Cys-SWCNT-CoTAPc) (5.1 x 10-3 cm s-1) is attributed to the possible effect of both the central metal on the phthalocyanine core and subsituents on the peripheral positions of the phthalocyanine rings. This work clearly proved that the aligned SWCNTs arrays exhibit much faster electron transfer kinetics to redox-active species in solutions compared to the randomly dispersed (drop-dried) SWCNTs. The advantageous electron transfer properties of the aligned Au-Cys-SWCNT-FeOHETPc electrode, coupled with its ease of fabrication and electrochemical stability, could be found useful in electrochemical sensing and catalysis. Thiocyanate ion was used as an analytical probe to examine the electrocatalytic properties of these modified gold electrodes. This work shows that SWCNT-FeOHETPc hybrid exhibits excellent sensitivity towards the detection of thiocyanate compared to electrodes containing SWCNT or FeTAPc or FeOHETPc only, indicating the ability of the SWCNTs to function as effective conductive nanowires for the detection of this important analyte. The electrochemical response of the FeOHETPc based electrodes was greater than their FeTAPc-based electrode counterparts, indicative of the impact of peripheral substituents on the phthalocyanine core towards electrocatalytic behaviour of these types of hybrids. Nevertheless, the exchange of the central metal as seen with the case of CoTAPc (see chapter 3), provide useful comparative electrochemical activity of this complexes versus FeTAPc with the same chemical environment with an indication of iron being the best as metal centre. FMCA or FDCA were covalently attached to the base Cysteamine monolayer to form the Au-Cys-FMCA and Au-Cys-FDCA, respectively. The same covalent attachment strategy was used to form the mixed SWCNTs and ferrocene-terminated layers (i.e., Au-Cys-SWCNT/FMCA and Au-Cys-SWCNT/FDCA). The impact of neighbouring SWCNTs on the electron transfer dynamics of the ferrocene molecular assemblies in acidic medium (0.5 M H2SO4) and in a solution (pH 7.2) of an outer-sphere redox probe ([Fe(CN)6]4-/ [Fe(CN) 6]3-) was explored. The electron transfer rate constants in both solution media essentially decrease as Au-Cys-FMCA > Au-Cys-SWCNT/FDCA > Au-Cys-FDCA > Au-Cys-SWCNT/FMCA. This trend has been interpreted in terms of several factors such as the locations of the ferrocene species in a range of environments with a range of potentials, the proximity /interactions of the ferrocenes with one another, and electrostatic interaction or repulsion existing between the negatively-charged redox probe and the modified electrodes. Square wave voltammetry was used to examine the catalytic behaviour of the electrodes. Au-Cys-SWCNT/FDCA proved to be the best electrode, possibly due to the repulsive interactions between the negatively charged SCN- and high number of surface –COOH species at the SWCNT/FDCA. This novel study has provided some useful insights as to how CNTs co-assembled with ferrocene-terminated thiols could impact on the heterogeneous electron transfer kinetics as well as the electrocatalytic detection of the self-assembled ferrocene layers. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

This thesis investigated the physical properties of the macrolide antibiotics: Erythromycin dihydrate (EM-DH), Roxithromycin monohydrate (RM-MH) and Azithromycin dihydrate (AZM-DH). The abovementioned hydrate compounds were investigated in terms of the hydrate-anhydrate crystal structure stability, dehydration and observed polymorphism under controlled temperature heating programs. Identified hydrate and anhydrate polymorphs were subjected to physical stability testing during controlled storage. EM-DH was characterized by thermal analysis (DSC, TGA), X-ray diffraction, FTIR and microscopy. Dehydration of EM-DH at temperatures of 100, 157 and 200°C (followed by supercooling to 25°C) produced the form (I) anhydrate (Tm =142.9°C), form (II) anhydrate (Tm = 184.7°C ) and amorph (II) (Tg = 118°C) respectively. The attempts to produce amorph (I) from melting (in vicinity of form (I) melt over temperature range 133°C to 144°C) and supercooling was unsuccessful due to the high crystallization tendency of the form (I) melt. Brief humidity exposure and controlled temperature (40°C)/ humidity storage for 4 days (0-96% RH) revealed hygroscopic behaviour for the anhydrate crystal (forms (I) and (II)) and amorph (II) forms. Form (II) converted to a nonstoichiometric hydrate where extent of water vapour absorption increased with increased storage humidity (2.1% absorbed moisture from recorded TGA at 96% RH). Amorph (II) exhibited similar trends but with greater water absorption of 4.7% (recorded with TGA) at 96% RH. The pulverization and sieving process of amorph (II) (at normal environmental conditions) was accompanied by some water vapour absorption (1.1%). A slightly lower absorbed moisture content of 3.3% (from TGA) after controlled 4 days storage at 40°C/ 96% RH was recorded. This suggested some physical instability (crystallization tendency) of amorph (II) after pulverization. The thermally induced dehydration of RM-MH by DSC-TG was evaluated structurally (SCXRD), morphologically (microscopy) and by kinetic analysis. Various kinetic analysis approaches were employed (advanced, approximation based integral and differential kinetic analysis methods) in order to obtain reliable dehydration kinetic parameters. The crystal structure was little affected by dehydration as most H-bonds were intramolecular and not integral to the crystal structure stability. Kinetic parameters from thermally stimulated dehydration indicated a multidimensional diffusion based mechanism, due to the escape of water from interlinked voids in crystal. The hygroscopicity of the forms RM-MH, Roxithromycin-anhydrate and amorph glass (Tg = 81.4°C) were investigated. Roxithromycinanhydrate (crystalline) converted readily to RM-MH which were found to be compositionally stable over the humidity range 43-96%RH. Amorphous glass exhibited increased water vapour absorption with increasing storage humidity (40°C/ 0-96% RH). TG analysis suggested a moisture content of 3.5% at 96% RH after 4 storage days. DSC and powder XRD analysis of stored pulverised amorphous glass indicated some physical instability due to water induced crystallization. Commercial AZM-DH and its modifications were characterized by thermal analysis (DSC, TGA), SC-XRD and microscopy. Thermally stimulated dehydration of AZM-DH occurred in a two-step process over different temperature ranges. This was attributed to different bonding environments for coordinated waters which were also verified from the crystal structure. Dehydration activation energies for thermally stimulated dehydration were however similar for both loss steps. This was attributed to similarities in the mode of H- bonding. Different forms of AZM were prepared by programmed temperature heating and cooling of AZM-DH. The prepared forms included amorphous glass (melt supercooling), amorphous powder (prepared below crystalline melting temperature), crystalline anhydrate and crystalline partial dehydrate. Humidity exposure indicated hygroscopic behaviour for the amorphous, crystalline anhydrate and crystalline partial dehydrate modifications. Both the crystalline anhydrate and partial dehydrate modifications converted to the stoichiometric dihydrate form (AZM-DH) at normal environmental conditions at ambient temperature. Both the amorph glass and amorph powder exhibited increased moisture absorption with increased humidity exposure. TG analysis of the pulverised amorph glass indicated a moisture content of 5.1% at 96% RH after 4 storage days. The absence of crystalline melt in DSC and presence of Tg (106.9°C) indicated the sample remained amorphous after pulverisation and storage for 4 days at 40°C/ 96% RH.

Magneto-structural correlations have been made for a number of pyridine and pyrazine complexes of iron(II) and copper(Il), involving anions of a range of coordinating abilities, for example, sulfonate, RS0₃⁻ (where R is CF₃, CH₃ or p-CH₃C₆H₄); halide, Cl⁻ Br⁻ or I⁻; pseudohalide, NCO⁻ or NCS⁻; perchlorate and hexafluoroarsenate. Structure was determined by infrared, electronic and Mössbauer spectroscopy and differential scanning calorimetry, and, in some instances, by single-crystal X-ray diffraction. Spectroscopic results were used to investigate the nature of both anion and neutral ligand coordination. In complexes of stoichiometry ML₄ (RS0₃)₂ (where M is Fe or Cu, L is pyridine, pyrazine or 2-methylpyrazine and R is CF₃, CH₃ or p-CH₃C₆H₄), the neutral ligands were found to adopt a unidentate mode of coordination. For several of these complexes, X-ray crystallography revealed a square-planar array of pyridine ligands around the central metal, with anions coordinated in a unidentate mode above and below this plane. A monomeric molecular structure results in which the paramagnetic centres are well isolated from each other giving rise to magnetically-dilute species. In complexes of stoichiometry M(pyz)₂X₂ (where M is Fe or Cu and X⁻ is CF₃S0₃⁻, CH₃S0₃⁻, Cl⁻, Br⁻, I⁻, C10₄⁻ or NCS⁻), pyrazine was found to coordinate through both nitrogen donor atoms and inorganic coordination polymers were produced. X-ray crystallography revealed a two-dimensional lattice in Cu(pyz)₂(CH₃S0₃)₂ with two distinct kinds of bridging pyrazine groups and monodentate sulfonate anions. For the remaining bis(pyrazine) complexes, spectroscopic evidence supports similar structures with unidentate anion coordination and bidentate bridging pyrazine ligands leading to sheet-like polymers. Cu(pyz)₂(CH₃S0₃)₂ and Fe(pyz)₂(NCS)₂ exhibit magnetic susceptibilities which reveal the antiferromagnetic nature of these materials (ˣmax at temperatures of 7.0 and 8.0 K respectively); the data were analysed in terms of a two-dimensional Heisenberg model. For the copper complex, in which the structure shows stronger pyrazine coordination along one dimension, the data were also analysed in terms of a linear chain model. Mössbauer spectroscopy showed Fe(pyz)₂(NCS)₂ to undergo a transition to a magnetically-ordered state at 9.2 K. The magnitude of the exchange coupling through bridging pyrazine in Fe(pyz)₂X₂ complexes (where X⁻ is CF₃S0₃⁻, CH₃S0₃⁻, Cl⁻, Br⁻, I⁻ or C10₄⁻) is considerably less than that present in either Cu(pyz)₂(CH₃SO₃)₂ or Fe(pyz)₂(NCS)₂. Spectroscopic evidence indicates that for Fe(py)₂(CF₃S0₃)₂ and complexes of stoichiometry M(pyz)X₂ (where M is Fe or Cu and X⁻ is CF₃S0₃⁻, p-CH₃C₆H₄S0₃⁻, Cl⁻ or NCO⁻) bridging anionic ligands are present and for the mono(pyrazine) complexes the neutral ligand also coordinates in a bridging mode. Fe(pyz)(CF₃S0₃)₂, Fe(pyz)(NCO)₂ and Cu(pyz)(CF₃SO₃)₂ all exhibit magnetic susceptibility data characteristic of antiferromagnetic materials (ˣmax at temperatures of 4.4, 38 and 7.0 K respectively). The magnetic susceptibilities for these materials were analysed in terms of the two-dimensional Heisenberg model and a linear chain model. Mössbauer spectroscopy shows both Fe(pyz)(CF₃S0₃)₂ and Fe(pyz)(NCO)₂ to undergo a transition to long-range magnetic ordering at temperatures of 3.9 and 27.0 K respectively. Low-temperature (4.2-130 K) magnetic susceptibility measurements for the iron(II) sulfonate compounds, Fe(RS0₃)₂ (where R is F, CF₃, CH₃ or p-CH₃C₆H₄) are reported. For the compounds where R is F, CF₃ or p-CH₃C₆H₄ the magnetic moment data were assessed in terms of crystal-field splitting effects. The magnetic moment data for ɑ and β forms of Fe(CH₃S0₃)₂ are indicative of antiferromagnetic exchange interactions and the characteristics of the susceptibility curve for the β isomer are explained on the basis of a transition from short-range to long range three-dimensional magnetic ordering at 22 K. / Science, Faculty of / Chemistry, Department of / Graduate

M.Sc. (Physics) / Please refer to full text to view abstract

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