In binary systems, surfactant molecules can self-assemble into a large variety of structures depending on their chemical structure, concentration and temperature. The properties and stability of the phases, their coexistence regions and the formation of metastable structures is of great importance not only for fundamental understanding, but also for applications in many fields including industry and medicine. This thesis presents studies of the equilibrium and non-equilibrium behaviour of two widely used surfactant systems. The understanding of the equilibrium behaviour of an aqueous surfactant system is often incomplete or partly incorrect, which is caused by experimental difficulties, long equilibration times and the occurrence of long-lived metastable states. By applying a set of complementary techniques and recording changes on different length scales, the equilibrium phase diagram of the surfactant didodecyldimethylammonium bromide (DDAB) in water has been studied and amended. Differential scanning calorimetry has been used to obtain thermodynamic parameters. The structure of phases and biphasic regions have been characterised by small angle X-ray scattering and microscopy, while the conformational properties of the surfactant molecules have been investigated using Raman spectroscopy combined with computational methods. The effects of impurities have been studied using analytical techniques and a sufficient purity of the samples could be ensured. As a result of the studies, a new crystalline phase which exists at temperatures below 16°C was found. This phase replaces the frozen lamellar phase (Lβ) in the previously reported phase diagram. The Lβ phase has been found to be a long-lived metastable phase. The amended phase diagram has been tested by studying phase transitions along isoplethal and isothermal paths. All experimental results could be explained in terms of the new phase diagram. The study of phase transition along isoplethal paths focused on the transition between the new crystalline phase (XWn) coexisting with a dilute monomer solution (W) and the lamellar phase (Lα). This transition was (except for a single composition DDAB≈3% DDAB) a non-isothermal transition involving the phase sequence: XWn +W → XWn + Lα → Lα upon heating and Lα → overcooled Lα → XWn +W upon cooling. The structural changes within the phases and their relative ratios could be characterised using small angle X-ray scattering, microscopy and Raman spectroscopy. During the dissolution of lamellar phases along an isothermal path, multilamellar wormlike interface instabilities (so called myelins) were found to grow from the lamellar/water interface into the water. The growth of these myelins as well as changes in the lamellar phase have been investigated using optical microscopy and direct observation. This has provided detailed quantitative information on the dynamics of myelin growth and the effect of the initial structure of the lamellar phase on the myelin growth. The dependence of the growing rate on surfactant concentration could be explained in terms of a previously reported model in which the osmotic pressure was stated to be the driving force for the myelin kinetics. It has been found that for lamellar phases in coexistence with a sufficient amount of crystals, the myelin growth could be suppressed. Preliminary measurements of a tertiary system, where the pure lamellar phase of DDAB was mixed with a crystalline phase formed by dioctadecyldimethylammonium bromide (DODAB), a DDAB analogue, were carried out. The myelin growth has also been studied for a second system, the non-ionic surfactant triethylene glycol monododecyl ether (C12E3), known for its formation of myelins of great stability. The optical methods were extended to confocal microscopy, resulting in a 3D image of the myelin formation, providing detailed quantitative information on myelin growth as well as on myelin size.

Brillouin spectroscopy probes the thermally generated pressure fluctuations (sound waves) which propagate in a material. The resulting information on sound velocity and absorption provides a fast and efficient method of monitoring high frequency (GHz) dynamics in the system being studied. In certain cases, structural information may also be inferred from changes in the Brillouin spectrum as a function of temperature, pressure or composition (in the case of multi-component systems). The aim of the work presented in this thesis was to integrate Brillouin spectroscopy into current soft condensed matter research projects at Edinburgh, namely (i) hydration in methanol-water mixtures and (ii) the behaviour of hard-sphere colloidal dispersions. A Brillouin spectrometer based on a Fabry-Perot interferometer was developed and tested, resulting in a high-resolution instrument operating at variable scattering vector (exchanged momentum), temperature and pressure. The technical aspects of this work were carried out in collaboration with a colleague. Data analysis routines were designed and implemented, enabling calibrated Brillouin spectra to be produced automatically from raw experimental data. Excellent agreement with results on several materials studied in the literature confirmed the accuracy and sensitivity of the spectrometer. The molecular details of hydration in methanol-water mixtures are of great interest due to the prototypical amphiphilic nature of the methanol molecule. The effect of deep cooling on the Brillouin spectrum across a wide range of methanol concentrations was studied in detail, resulting in the first observation of an anomalous increase in sound velocity and maximum in sound absorption at intermediate compositions. A similar effect was then found at higher temperature in aqueous tertiary butanol, and was identified in a brief survey of several other aqueous solutions. High pressure Brillouin spectra indicate that this anomalous behaviour may also be present in pure water. It is suggested that these novel effects may be due to the presence of a relatively unperturbed water structure in the aqueous solutions studied, even at quite high solute concentration. Preliminary results from a neutron diffraction experiment performed on a 40% by mass methanol-water mixture were consistent with this hypothesis. Brillouin spectroscopy was also used to study the propagation of high frequency sound in monodisperse colloidal suspensions of sub-micron hard spheres. A second longitudinal sound mode was observed for scattering vectors of magnitude greater than pi/d where d is the diameter of the spheres. These results are the first reproduction and extension of the pioneering work in the field, which identified the additional mode with a surface acoustic excitation, propagating between adjacent spheres via an evanescent wave in the solvent. The new results show that the second mode is extinguished at a particular scattering vector - an effect not reported previously. It is suggested that this extinction is due to the minimum in the form factor for elastic scattering from a single sphere.

This thesis presents enhanced analytical methods developed for complex aqueous sample analysis based on solid phase microextraction (SPME). First, the laboratory evaluation of the kinetic calibration approach in aqueous sample analysis using SPME is discussed. A modified SPME device, Polydimethylsiloxane (PDMS) rod passive sampler, was developed and the kinetic calibration method based on the standard preloaded in the extraction phase was applied to determine the time-weighted average (TWA) concentration of organic pollutants in water. Later, the SPME technique was used to investigate the complex interactions between the organic pollutants and humic organic matter (HOM) present in the aqueous samples. The kinetics of the SPME approach in complex aqueous samples was studied. The concentration of freely dissolved analytes and the total concentration of the target analytes in the sample matrix were determined by SPME sampling. The usefulness of the SPME approach for binding studies was further demonstrated by determining the sorption coefficient, a useful parameter for studying the bioavailability of the organic pollutants in the environment. In addition, the commercial Computational Fluid Dynamics (CFD) software COMSOL Multiphysics was used to predict the kinetics of analyte extraction and flow pattern under different experimental conditions using the SPME technique. A good agreement between the prediction and the experimental data confirms the advantages of the CFD application for experimental optimization thus minimizing the need of extensive experiments.

This thesis presents enhanced analytical methods developed for complex aqueous sample analysis based on solid phase microextraction (SPME). First, the laboratory evaluation of the kinetic calibration approach in aqueous sample analysis using SPME is discussed. A modified SPME device, Polydimethylsiloxane (PDMS) rod passive sampler, was developed and the kinetic calibration method based on the standard preloaded in the extraction phase was applied to determine the time-weighted average (TWA) concentration of organic pollutants in water. Later, the SPME technique was used to investigate the complex interactions between the organic pollutants and humic organic matter (HOM) present in the aqueous samples. The kinetics of the SPME approach in complex aqueous samples was studied. The concentration of freely dissolved analytes and the total concentration of the target analytes in the sample matrix were determined by SPME sampling. The usefulness of the SPME approach for binding studies was further demonstrated by determining the sorption coefficient, a useful parameter for studying the bioavailability of the organic pollutants in the environment. In addition, the commercial Computational Fluid Dynamics (CFD) software COMSOL Multiphysics was used to predict the kinetics of analyte extraction and flow pattern under different experimental conditions using the SPME technique. A good agreement between the prediction and the experimental data confirms the advantages of the CFD application for experimental optimization thus minimizing the need of extensive experiments.

Urea aqueous solution is ubiquitously used to denature protein. Regardless of its extensive use, the mechanism is still unclear and remains an active field of study. There have been two proposed mechanisms, the direct and indirect. The indirect mechanism, which attributes the ability of urea of changing water structure, is susceptible since many research works show that there is little effect of urea on water structure. The current study provided evidence for the indirect mechanism by demonstrating that the introduction of urea slightly changes the water structure in the hydrophobic interfacial areas. In the current study, the urea aqueous solution systems with either gas-liquid or hydrophobic interface are studied by MD simulations, and the structures of water near the interfacial areas are analyzed in terms of density, orientation and number of hydrogen bonds. For each kind of interface, systems with four different urea concentrations are included, ranging from 0M to 8M. The results show slight change of water structure by the urea solute on the hydrophobic interface in terms of the orientation and number of hydrogen bonds per water molecule.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

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The purification of pepsinogen from the stomach of red perch using aqueous two phase systems (ATPS) formed by polyethylene glycol (PEG) and salt at 4°C was optimized. Salt type, salt concentration, PEG molecular weight and PEG concentration had significant effects on total volume (TV), volume ratio (VR), enzyme activity (AE), protein content (CP), specific activity (SA), purification fold (PF) and recovery yield (RY). (NH4)2SO4 at 15% w/w concentration was selected as the optimum salt type and concentration. PEG 1500 at 18% w/w concentration was selected as the optimum PEG molecular weight and concentration. 15% (NH4)2SO4-18% PEG 1500, the optimal ATPS, was compared with ammonium sulfate fractionation (ASF). ATPS gave better partition of pepsinogen (SA of 5.40 U/mg, PF of 5.20 and RY of 86.6%) than ASF (SA of 2.55 U/mg, PF of 2.46, RY of 70.4%). / This is the electronic copy of partition of pepsinogen in aqueous two phase system method.

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The primary focus of the research is to extend the principles of Nanofiltration(NF) to non-aqueous systems using solvent-resistant NF membranes. Several differentlevels of interaction are introduced when organic solvents are used with polymericmembranes and thus quantification of polymer-solvent interactions is critical. Puresolvent permeation studies were conducted to understand the mechanism of solventtransport through polymeric membranes. Different membrane materials (hydrophilic andhydrophobic) as well as different solvents (polar and non-polar) were used for the study.For example, hexane flux at 13 bar through a hydrophobic silicone based NF membranewas ~ 0.6 x 10-4 cm3/cm2. s. and that through a hydrophilic aromatic polyamide based NFmembrane was ~ 6 x 10-4 cm3/cm2. s. A simple model based on a solution-diffusionapproach which uses solvent physical properties (molar volume, viscosity) andmembrane properties (surface energy, etc) is used for correlating the pure solventpermeation through hydrophobic polymeric membranes.Solute transport studies were performed using organic dyes and triglycerides inpolar and non-polar solvents. For example, the rejection of Sudan IV (384 MW organicdye) in n-hexane medium is about 25 % at 15 bar and that in methanol is about –10 % atabout 20 bar for a hydrophobic (PDMS-based) membrane. However, for a hydrophilicpolyamide based NF membrane, the direction of separation is reversed (86 % in methanoland 43 % in n-hexane). From our experimental data with two types of membranes it isclear that coupling of the solute and solvent fluxes cannot be neglected. Two traditionaltransport theories (Spiegler-Kedem and Surface Force-Pore Flow model) that considercoupling were evaluated with literature and our experimental solute permeation data. Amodel based on a fundamental chemical potential gradient approach has been proposedfor explaining solute separation. The model uses solute, solvent and membrane physicalproperties and uses the Flory-Huggins and UNIFAC theories as activity coefficientmodels. This model has been used to obtain a correlation for the diffusion coefficients ofsolutes in hexane through a hydrophobic membrane. This correlation along withconvective coupling can be used to predict separation behavior for different solutes and atdifferent temperatures.