Excess molar volumes have been determined for four ternary chlorobenzene + dibutyl ether + alkane mixtures at 25°C. Results of these measurements are used to test the applications and limitations of BAB, Redlich-Kister, Kohler and Hwang et al. cubic models. For the systems studied, Redlich- Kister, Kohler and Cubic models were found to provide reasonable predictions. Differences between experimental and predicted ΔV^ex_123 values were about ±0.020 cm^3mol^-1 or less at most ternary compositions. Solubilities are reported for anthracene in binary mixtures containing propanol and butanol with alkanes at 25°C. Results of these measurements are used to test the NIBS/Redlich-Kister expression. The three-parameter form of this expression is found to provide reasonable mathematical representation with deviations between experimental and back-calculated values being less than ±1%.

Since resin composites were first presented to dentistry more than half a century ago, the composition of resin composites has developed significantly. One major change was that the reinforcing filler particles were reduced in size to generate materials of a given filler content that display better physical and mechanical properties. Resin composites may absorb water and chemicals from the surrounding environment but at the same time, composites may release constituents to their surroundings. The physical/mechanical properties of a restorative material provide an indication of how the material will function under stress in the oral environment. The aims of this research were to examine the effects of water at 37°C on the physical and mechanical properties, and the effect of food-simulating solvents of a variety of experimental and contemporary resin composites, on the surface properties. Eight representative resin composites were selected (Exp. VT, BL, NCB, TEC, GSO, XB, VDF and CXD). Due to the recent development of bulk fill materials on the market during the course of this research, the post-cure depth of cure of new bulk fill materials was also investigated. Five representative resin composites were selected: TBF, XB, FBF, VBF and SF. Water sorption and solubility were investigated at 37°C for 150 days. Sorption and solubility are affected by the degree of hydrophilicity of the resin matrix. The bulk fill materials examined showed the lowest water sorption and solubility. Laser scan micrometer (LSM) was used to investigate hygroscopic expansion. The extent of the hygroscopic expansion positively correlated with the amount of water sorption. The effect of water on fracture toughness was also examined. A self-adhesive hydrophilic resin matrix decreased in fracture toughness after 7 days of storage at 37°C. By contrast, the least water absorbed bulk fill material increased in fracture toughness over time. The effect of food-simulating solvents (distilled water, 75% ethanol/water and MEK) on surface micro-hardness, colour stability and gloss retention were investigated. The MEK solvent resulted in the lowest micro-hardness and the greatest colour change (ΔE) for most of the examined composites, while the 75% ethanol/water solution caused the greatest loss in gloss for most of the examined composites. A highly filled nano-composite showed the best result over time, regardless of the condition of storage. Surface micro-hardness profiles were used as an indirect method to assess the depth of cure of bulk fill resin composites. The examined bulk fill resin composites can be cured to an acceptable depth (4 mm).

This thesis explores the robustness and the versatility of pressurized hot water extraction (PHWE) for a variety of analytes and matrices. Applications discussed include: selective extraction of alkaloids in goldenseal followed by their degradation studies; in-cell clean-up of pesticides in medicinal plants employing custom made molecularly imprinted polymers (MIPs) sorbents; in-cell pre-concentration followed by desorption of aflatoxins in plants with MIPs; desorption of pesticides from electrospun nanofiber sorbents; and removal of templates from MIPs sorbents. It was demonstrated that selective extractions could be achieved by just changing the temperature of water while adjusting the pressure. For instance, the alkaloids in goldenseal (hydrastine and berberine), were extracted at 140 °C, 50 bars, 1 mL min⁻¹ in 15 min; organochlorine pesticides from medicinal plants were extracted at 260 °C, 80 bars, 1 mL min-1 in 10 min; while aflatoxins AFG2, AFG1, AFB2 and AFB1 were extracted at 180 °C, 60 bars and a flow rate of 0.5 mL min⁻¹ in 10 min. The selectivity of PHWE was further enhanced by combining it with selective MIPs sorbents at higher temperatutes. In-cell clean-up of interfering chlorophyll was successfully removed from the medicinal plants during pesticides analysis while clean-up of aflatoxins AFG2, AFG1, AFB2 and AFB1 was achieved in two extraction cells connected in series. Ultrasound was also combined with PHWE for extraction of hydrastine and berberine at 80 °C and 40 bars in 30 min. PHWE was further evaluated for removal of templates from quercetin, phthalocynine and chlorophyll MIPs. The templates were thoroughly washed off their MIPs within 70 min with PHWE compared to over 8 h for Soxhlet and ultrasound assisted extraction. Pesticides were also desorbed from electrospun nanofibers at 260 °C, 80 bars in 10 min employing only water at 0.5 mL min⁻¹. In the light of green chemistry, the decrease in the usage of organic solvents was 100%, resulting in no organic solvent waste.

Solvent-free reactions possess advantages compared to the solvent route, such as shorter reaction times, less use of energy, better yields, etc. Herein, the synthesis and characterization of bisferrocenylimines and arylbisamines are described. Reduction of the above compounds with LAH resulted in the formation of bisferrocenylamines and arylbisamines, respectively. The coordination chemistry of all the above compounds to rhodium(I) is also discussed in the prepared complexes [Rh(COD)(NN)]ClO4, where NN = bisferrocenylimines, and [Rh(COD)(NN)]BF4, where NN = bisferrocenylamines and arylbisamines. X-ray crystal structures of the complexes [Rh(COD)(NN)]ClO4 ([3.2] and [3.3]) have been obtained. Complexes of the type [Rh(COD)(NN)]BF4 were characterized with IR and UV-vis spectroscopy, cyclic voltammetry and conductometry. The catalytic activity of the complexes was also investigated: [Rh(COD)(NN)]ClO4 for the polymerization of phenylacetylene and [Rh(COD)(NN)]BF4 for the hydroformylation of styrene.

The electrochemical oxidation of CoCl2(PPh3)2 was investigated in a mixture of acetonitrile and pentanol (1:1) at a platinum disk working electrode using Cyclic Voltammetry (CV) and Chronoamperometry. Elemental Analysis and Infrared Spectroscopy were used to characterise the synthesized compounds i.e. CoCl2(PPh3)2 and CoCl(PPh3)3. Cyclic Voltammetry was utilised for the examination of different working electrode materials that could be used for the anodic voltammetric studies of CoCl2 (PPh3)2, to characterise the reactants and products of each electrode reaction, to investigate the chloride binding ability to a CoCl(PPh3)3 complex, and to evaluate the electrocatalytic substitution of chloride by PPh3 from the complex CoCl2(PPh3)2. Use of ferrocene as an internal standard during the anodic studies of CoCl2(PPh3)2 was also evaluated. The number of electron involved in the electrode process, CoII to CoIII from CoCl2(PPh3)2 and diffusion coefficient of ferrocene in a mixture of acetonitrile and pentanol (1:1) were determined using Chronoamperometry. Ultraviolet-Visible (UV-Vis) and 31P Nuclear Magnetic Resonance (31P NMR) spectra were used to assist with the characterisation of the electrode reactions involved during oxidation of CoCl2(PPh3)2. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted

The purpose of this Master's Project was to develop an Acid-Base Titration Simulator. It was also to be a part of the California State University - San Bernardino's GTSS, Generic Tutorial System for the Sciences, project. The main benefit is that students will be able to conduct titration experiments over the Internet without being in the laboratory and without costly equipment or dangerous chemicals. Instructors at the high school and college level can demonstrate the key principles of titration.

Flash photolysis techniques were applied to studies of solvent displacement by Lewis bases (L) from solvated metal carbonyl complexes of Cr, Mo, and W. On the basis of extensive studies of the reaction rate laws, activation parameters , and linear-free-energy-relationships, it was concluded that the mechanisms of solvent displacement reactions depend on the electronic and steric properties of the solvents and L, as well as the identities of the metal atoms. The strengths of solvent-metal bonding interactions, varying from ca. 7 to 16 kcal/mol, and the bonding "modes" of solvents to metals are sensitive to the structures of the solvent molecules and the identities of the metal centers. The results indicate dissociative desolvation pathways for many arene solvents in (solvent)Cr(CO)_5 (solvent = benzene, fluorobenzene, toluene, etc.) complexes, and are consistent with competitive interchange and dissociative pathways for (n-heptane)M(CO)_5. Different types of (arene)-Cr(CO)_5 interactions were suggested for chlorobenzene (CB) vs. fluorobenzene and other non-halogenated arenes, i.e. via σ-halogen-Cr bond formation in the CB solvate vs. π-arene-Cr bond formation through "isolated" double bonds in solvates of the other arenes. The data also indicate the increasing importance of interchange pathways for solvent displacement from the solvates of Mo and W vs. that of Cr.

No description available.

For its inherent advantages, such as lightweight, low cost, flexibility, and opportunity to cover large surface areas, organic solar cells have attracted more and more attention in both academia and industry. However, the efficiency of organic solar cell is still much lower than silicon solar cells, but steadily rising as it now stands above 8%. The architecture of bulk heterojunction solar cells can improve the performance of organic solar cell a lot, but these improvements are highly dependent on the morphology of photoactive layer. Therefore, by controlling the morphology of photoactive layer, most commonly composed of a P3HT donor polymer and PCBM small molecule, the performance of organic solar cells could be optimized. The use of solvent additives in the solution formulation is particularly interesting, because it is a low cost method of controlling the phase separation of the photoactive layer and possibly removing the need for subsequent thermal and solvent vapor annealing. However, the role of the solvent additive remains not well understood and much debate remains on the mechanisms by which it impacts phase separation. In the first part of this thesis, we investigate the role of the solvent additive on the individual components (solvent, donor and acceptor) of the solution and the photoactive layer both in the bulk solution, during solution-processing and in the post-processing solid state of the film. In the second part of this thesis, we investigate the role of the additive on the blended solution state and resulting thin film phase separation. Finally, we propose a new method of controlling phase separation based on the insight into the role of the solvent additive. In the first part, we used an additive [octandiethiol (OT)] in the solvent to help the aggregation of P3HT in the solution. From the UV-vis experiments, the crystallinity of P3HT in the solutions increased while it decreased in thin films with steady increase of additive concentration. This method could be used for one step, annealing-free fabrication of organic solar cell with high performance. The solution can potentially be used to prepare ink for the large scale roll-to-roll ink-jet printing of P3HT thin films. Secondly, from the experiments it is found that differences in the evaporation rate and solubility of the components of the photoactive layer may be part of the reason for morphological changes. With lower evaporation rate than the host solvent, the additive concentration in the solution keeps increasing with time during the final stages of spin coating. In addition, the phase separation is increased with the increase of additive concentration, as demonstrated by AFM and TEM. By controlling the additive concentration, it is possible to control the phase separation of photoactive layer in pristine device. It is also found that the additive can change the wetting ability of the solvent to produce films with high surface coverage. With this information in hand, we modified the solution process of BHJ layers. A layer of crystals was deposited from the OT-containing solution by postponing the start of the spin coating for several minutes (delay time) after the solution is dropped on the surface of substrate. We found this to be a very effective method of increasing the phase separation and crystallinity of the photoactive materials. This effect was not possible when using oDCB solvent without any additive.

The aim of this diploma thesis is a study and description of a mutual interaction of solvents belonging to the green solvents group, specifically glutaric acid esters and selected acrylic and alkyd coating systems. In the experimental part of this thesis there is a study of a resistance of the coating systems to solvents by the spotting method, which is subsequently then combined with an adhesion experiment of the coating film by the cross-cut test. Those experiments are made according to matching methods in valid version.