In this thesis, we examine the relationship between structure and dynamics in supercooled liquids from five unique perspectives. We first study a static length scale in the liquid and compare its growth on decreasing temperature with the growth of the logarithm of relaxation times, and find them to be almost strongly correlated. We find that this length scale can distinguish between several specially chosen model liquids whose structure at the level of two-body correlations are identical but whose dynamics at a given temperature are quite different. We then study the number of normal modes necessary to capture the rearrangements in a two-dimensional supercooled liquid as it moves between inherent structures. We find that the number of modes is quite small and decreases as the system is further cooled. After that, we study the effect of a frozen amorphous boundary on the dynamics of supercooled liquids and find that the range of the effect plateaus near that system's mode coupling temperature. We also identify a dynamical crossover at a higher temperature from these data by contrasting the relaxation behavior in the directions perpendicular and parallel to the boundary. After this work, we compare particle mobility with the position of particles deemed to be in preferred local packing arrangements. We find that the correlation between slow dynamics and the location of these locally preferred structures is highly dependent on the model investigated. Finally, we study supercooled liquids that have a fraction of particles randomly fixed in equilibrium positions. We find from annealing and rapid heating experiments on these samples behavior reminiscent of experimentally produced ultrastable glasses.

Polymer-Surfactant (P-S) systems and their implications both in industry and academia have been studied for the last fifty years. Despite the fact that the majority of synthetic and biological systems have a multicomponent nature, most previous studies focused on molecular interactions of individual polymers and surfactants in aqueous solutions, at the air/water interface or at the solid/water interface. P-S interactions in multicomponent systems have not received sufficient attention. Among the important issues that remain unresolved, the following are of particular significance: a) lack of information on P-S systems phase behavior in the presence of a third component which is widely used in industrial applications and of academic interest, b) insufficient quantitative information on competitive interactions of all species in the system and uncertainty on how molecules conform upon interaction and, c) lack of mathematical models to describe P-S interactions in a multicomponent environment. To address the unresolved issues, a study focusing on the mechanisms of interaction of an oppositely charged polyelectrolyte-surfactant (PE-S) pair in the presence of fatty acid (FA) was carried out. Experimental results using surface tensiometry, light scattering, zeta potential and, nuclear magnetic resonance (NMR) showed that the FA solubility in the system determined the overall phase behavior of the multicomponent mixture. In a system containing FA at a concentration above the solubilization limit of the surfactant, FAs form solid aggregates. Such aggregates were found to possess a considerable negative surface charge, consequently, preferential binding of the polycation to FA aggregates was observed and the usual tendency of PE-S pair to form a complex was inhibited. These results were useful to understand the polyelectrolyte-induced flocculation disruption by FA aggregates in emulsions systems. In a system containing FA at a concentration below the solubilization limit of the surfactant, the FA was found to be mostly solubilized forming mixed micelles with the surfactant. NMR revealed detailed information on the competitive binding behavior of both the fatty acid and the surfactant, including the morphology of aggregates at the polymer chain. Furthermore, solid state NMR showed how the structure and composition of the actual PE-S complex changed in the presence of FA. Finally, the law of mass action model is successfully employed to describe the PE-S surface tension profile in the presence of FAs.

This thesis describes developments towards incorporating spiropyran functionality into metal-organic frameworks (MOFs). Chapter 1 outlines the reported literature concerning the study of photochemistry with respect to MOFs; such materials have demonstrated potential as both alternative environments for the study of photoactivated processes and platforms to integrate photosensitive moieties. Incorporation of photoactive groups into MOFs has enabled these supramolecular materials to be altered chemically and physically via photo-initiated processes. Existing studies into reversible photoswitching groups are largely focussed on azobenzene. The chronological development of azobenzene incorporation into MOFs reflects the evolving strategies of exploiting this functionality to achieve photocontrol over the properties of MOF materials. These advances in accommodating photoswitching azobenzene into MOFs have been applied in reported studies with other photochromic groups and taken into consideration with the work described herein concerning spiropyrans. Chapter 2 focusses on the preparation of a carboxylic acid functionalised salicylaldehyde 3-formyl-4-hydroxybenzoic acid (H2L1), a key precursor in the synthesis of carboxylic acid functionalised spiropyrans. The serendipitous outcome in solvothermal reaction of H2L1 and copper nitrate in dimethylformamide affords {Cu2L12·(DMF)2(H2O)}n (1-Cu-DMF) which has been crystallographically characterised and is further described in this chapter. Channels run through the direction of the crystallographic a-axis of 1-Cu; its connectivity and porosity is retained upon solvent exchange of the single crystals with ethanol and tetrahydrofuran. Gas sorption experiments show 1-Cu exhibits type I adsorption behaviour with a Brunauer-Emmett-Teller (BET) surface area of 948 ± 1 m2 g−1. Notably, 1-Cu adsorbs negligible quantities of methane compared to carbon dioxide and other C2Hn hydrocarbons; the selectivities are confirmed by analysis via the ideal adsorbed solution theory (IAST) and Henry’s law. Of particular importance, 1-Cu demonstrates exceptional selectivity for acetylene, which has applicability in separation technologies for the isolation of acetylene. Chapter 3 details the design and synthesis of a series of carboxylic acid functionalised spiropyrans and bisbenzospiropyrans. These compounds serve as ligand precursors for MOFs but also have interesting photophysical properties as organic compounds, which are studied in this chapter. Condensation of prefunctionalised fragments, H2L1 and carboxylic acid functionalised Fischer’s base 5, afforded a novel dicarboxylic acid functionalised spiropyran H2L2. A second synthetic route to extended ligand precursors, via Suzuki-Miyaura cross coupling of ethyl ester functionalised boronic acids to dibrominated photoactive cores and subsequent hydrolysis, is described. Crystallographic characterisation of the ethyl esters indicates flexibility of the core moieties around the spiro carbon. Comparison of the UV-visible absorption spectra shows the properties of related spiropyrans and bisbenzospiropyrans to be influenced by electronic effects arising from both the type and positioning of the functional groups. The fluorescence quantum yields of novel spiropyrans 13, 15 and H2L5 have been determined as 0.025, 0.032 and 0.068 respectively. Cyclic voltammetric experiments show the electrochemical behaviour of spiropyrans to be influenced primarily by electronic effects related to the type of functional group attached, whereas the electrochemical properties of bisbenzospiropyrans is dominated by electronic effects arising from the positioning of the functional groups. Density functional theory (DFT) calculations of the spectroscopic properties are described and are consistent with experimental observations. Chapter 4 describes investigations to incorporate the carboxylic acid compounds prepared in Chapter 3 into framework materials. To mitigate potential instability problems from using solely photoresponsive and highly flexible components, co-crystallisation with pillaring agents was considered. Reaction of H2L2 with zinc nitrate and a dipyridyl terephthalamide pillaring agent L7 affords coordination network 2 Zn. Two isomers, {Zn(L2)(syn-L7)·(DMF)3(H2O)}n (2-syn-Zn) and {Zn(L2)(anti-L7)·(DMF)3.5(H2O)1.5}n (2-anti-Zn), have been crystallographically characterised; their differences rest upon the conformations adopted by ligand L7. The structure of the 2 anti Zn isomer has higher potential porosity, appearing as rhomboid channels running down the direction of the crystallographic b-axis. The two dimensional sheets of both 2-syn-Zn and 2-anti-Zn are linked in a third dimension through hydrogen bonding interactions between the carboxylate of (L2)2− and amide moiety of L7 in adjacent layers. UV irradiation (325 nm) of single crystals of both forms of 2 Zn initiates a growth in fluorescence of the material observed in situ on a Raman microscope. In situ monitoring of the fluorescence using a 785 nm laser shows a decay over 23 hours to recover the original Raman spectrum of the material. The fluorescence decay can be fitted to a biexponential process; the faster process (13 270 s−1 and 1290 s−1, 2-syn-Zn and 2-anti-Zn respectively) is approximately an order of magnitude greater than the slower process (3980 s−1 and 350 s−1 respectively). DFT calculations suggest the theoretical spectroscopic and electrochemical properties of (L2)2− are not significantly changed by coordination to zinc in 2-Zn. The structures 2-syn-Zn and 2-anti-Zn are the first known examples of spiropyran functionality being incorporated into frameworks.

In this thesis, surface electrocatalysis of several energy-conversion-relevant redox reactions in ionic liquid electrolytes is described. The first oxidation process investigated is the formation of surface oxide films on Pt electrodes by trace water oxidation in protic ionic liquids (PILs). This is followed by investigation of the oxidation of hydrazine (N2H4), formic acid (HCOOH), ethanol (EtOH) and dimethyl ether (DME) in PILs and a description of the role played by surface oxides during each oxidation process. Finally, the electrocatalytic reduction of CO2 at a variety of electrode materials is explored in room temperature aprotic ionic liquids. The data reveal that the surfaces of Pt electrodes become covered with oxide layers due to oxidation of trace water, which is omnipresent in PILs, at positive potentials (E > 1.0 V vs. Pd-H). X-ray photoelectron spectroscopy (XPS) shows that the oxide layers grow to form thick films as the potential is made more positive and as the temperature and water concentration of the PILs are increased. The mechanism and kinetics of oxide film growth are also discussed. Voltammetric analysis shows that the presence of residual surface oxides activates Pt electrodes towards electrooxidation of N2H4. Furthermore, immersion of oxidized Pt electrodes in N2H4-containing PILs deactivates the electrode indicating that N2H4 reacts with the residual surface oxides. Oxidation of HCOOH at Pt catalyst in PILs occurs mainly by dehydration plus COads oxidation at a potential that coincides with the onset of the formation of Pt surface oxides. Compared to Pt electrocatalysts, the overpotential for electrooxidation of HCOOH is higher at Au catalyst but lower at Pd catalyst. Oxidation of trace water in PILs at Pt also plays a pivotal role during the electrocatalytic oxidation of EtOH and DME in the PILs. Oxidation of both EtOH and DME coincides with coverage of the Pt surface by the adsorbed oxide species that helps to activate both processes by oxidizing the adsorbed poisoning CO and CO-like intermediate species via a 'bifunctional' reaction mechanism. Generally, higher overpotentials are observed for each oxidation, and higher activation energies are measured for EtOH oxidation in PILs than in aqueous electrolytes. Finally, it is shown that CO2 electroreduction takes place at lower overpotentials at Au and Ag electrocatalysts than at Cu, Pt and boron doped diamond (BDD) electrodes in the presence of ionic liquid electrolytes. Ag electrocatalysts reduce CO2 at ~0.2 V lower potential when 1-ethyl-3-methylimidazolium ethylsulphate [emim][EtSO4] is used as supporting electrolyte in acetonitrile compared to when the conventional supporting electrolyte tetrabutylammonium hexaflourophosphate [TBA][PF6] is used. CO is a product of CO2 reduction at Ag catalyst and the results highlight that Ag and imidazolium-based ILs could be a promising system for reduction of CO2 to CO at low overpotentials.

Includes bibliographical references. / 1 v. : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (D.Sc.)--University of Adelaide, Dept. of Chemistry, 1998

We report a performance comparison of two linear-scaling methods which avoid the diagonalization bottleneck of traditional electronic structure algorithms. The Chebyshev expansion method (CEWI) is implemented for carbon tight-binding calculations of large systems and its memory and timing requirements compared to those of our previously implemented conjugate gradient density matrix search (CG-DMS). Benchmark calculations are carried out on icosahedral fullerenes from C60 to C8640 and the linear scaling memory and CPU requirements of CEM demonstrated. We show that the CPU requisites of CEM and CG-DMS are similar for calculations with comparable accuracy.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 109-111). Available also in a digital version from Dissertation Abstracts.

No description available.

No description available.

In this thesis, attempts have been made to correlate some equilibrium properties of microemulsions with the formation and stability of macroemulsions. Studies have been mainly limited to water-in-oil (W/O) systems stabilised by pure nonionic surfactants of the poly-oxyethylene alkyl ether (CnEm) type. Initially however, a brief account is presented of the behaviour of W/O microemulsions stabilised by commercial nonionic surfactants of the type used in foods.A detailed study of the equilibrium behaviour of W/O microemulsions stabilised by tetra-oxyethylene mono-n-dodecyl ether, C12E4,in hydrocarbon oils is presented. Aggregates form above a certain surfactant concentration in the oil, designated the critical microemulsion concentration, cμc. Changes in the monolayer curvature induced through changing the temperature, salt concentration and the nature of the oil phase, are discussed in terms of an effective surfactant molecular geometry. The effect of solubilisation of protein into the dispersed aqueous phase is also presented.The corresponding W/O macroemulsions prepared with these systems at concentrations in excess of the cμc breakdown primarily by droplet sedimentation. There appears to be an optimum surfactant concentration at which maximum stabilisation is achieved. This is approximately equal to the cμc of the surfactant in the oil phase. Addition of microemulsion droplets to the oil dramatically increases the rate of oil phase resolution. For a fixed concentration of aggregated surfactant, the acceleration rate is rather insensitive to the size of the microemulsion droplets. These findings are reasonably consistent with a depletion flocculation mechanism in which microemulsions are assumed to behave as hard spheres and are excluded from the intervening region between approaching emulsion droplets.Microemulsion phase behaviour is also reported for oil phases containing different concentrations of medium and long chain length triglycerides (MCT, LCT) in heptane. The critical microemulsion concentration is observed to increase dramatically upon increasing the concentration of triglyceride. Additionally, the enthalpy change upon transfer of a mole of C12E4 monomers from the oil phase to the preferred microemulsion droplet curvature becomes significantly less exothermic as the concentration of MCT in the oil phase increases.The breakdown of W/O macroemulsions produced with these triglyceride systems is also consistent with a depletion flocculation mechanism. Emulsions prepared with 75% MCT as the oil phase undergo coalescence once an approximately closepacked droplet volume fraction is achieved. It is shown that as the cμc increases (through the addition of MCT or increasing the temperature), the stability of the emulsion dramatically decreases.Using a technique of time-resolved fluorimetry, the rate of exchange of probe molecules between microemulsion droplets has been determined. The exchange rate is always slowest at the solubilisation phase boundary where inter-droplet attractions are a minimum. The rate constants at this phase boundary are similar for aggregates formed in both heptane and in an equal volume ratio mixture of heptane : MCT. The possible relevance to the magnitude of the exchange rate constant of energies associated with bending the surfactant monolayer and desorbing surfactant from the droplet surface are considered.This technique has also been applied to three surfactant systems for which monolayer bending rigidities have previously been reported. Microemulsion exchange rates measured at equivalent positions on the solubilisation phase boundary increase as the monolayer rigidity decreases. The stability of the corresponding W/O macroemulsions is also observed to follow this order, the fastest water resolution rates being observed for the systems with the lowest monolayer rigidities.