STUDENT RESEARCH PROGRAMS


CORRELATIONS BETWEEN STRUCTURE AND BIODEGRADABILITY OF SUGAR BASED SURFACTANS

Irene Baker (PhD - in progress, CSIRO Division of Chemicals and Polymers, Clayton, Victoria)

The objective of this work is to provide an understanding of how performance and environmental acceptability of surfactans can be optimised simultaneously. The areas of interest include: The biodegradability of an array of surfactant structures have been determined. Using HPLC and NMR analysis methods, it has been shown that sucrose laureate is degraded via initial hydrolysis of the ester bond, while sucrose a-sulfolaurate is degraded via initial oxidation of the alkyl chain. This explains the slower rate of biodegradation of the latter surfactans. Biodegradation of sucrose laureates is also inhibited in the presence of a-methyl or ethyl groups but to a lesser extent. The biodegradation pathway of sucrose a-ethyl laureate was also investigated. Evidence concerning the biodegradation pathway of this compound was less conclusive. However it was shown that it is at least partly degraded via initial alkyl chain oxidation. Two dimensional NMR techniques were used to study the structure of intermediate metabolities formed during the biodegradation of sucrose a-sulfolaurate. The biodegradation curves obtained for the array of surfactants have been analysed and first order rate constants determined. These show the general trends of how structure effects biodegradability. Some preliminary modelling of the hydrolysis sucrose laureate and the subsequent incorporation of the products by bacteria has been concluded. Our analysis shows that the rates of hydrolysis and of uptake into cells are of the same order of magnitude. We concluded that the ultimate degradation curve reflects a combination of both processes, rather than a single rate determining step. The rates of chemical hydrolysis of three sugar ester surfactants in the presence of hydroxide ion were also measured at various temperatures. The surfactants studied were sucrose laureate, sucrose a-sulfolaurate and sucrose a-ethyl laureate. This study suggests that the substituents inhibit hydrolysis because of both electronic and steric effects. By analogy, it is concluded that steric effects are also important in controlling the rate of the enzyme mediated hydrolysis which occurs during biodegradation.

INCIPIENT SLUMPING

Jamie Chamberlain (PhD - in progress, APA/AMPC)

The focus of this research is to provide a quantitative understanding of the slump test and variants of the slump test. The slump test is a cheap, easy way of measuring the shear yield strength of a mineral tailings slurry. However, these tests currently need to be calibrated with a vane rheometer. A better theoretical understanding of the slump test is desired so that rheological tests can be carried out independently of the vane rheometer. The problem of analysing the stresses in a cylinder of slurry under its own weight has been identified as a useful starting point for understanding the slump test. This problem has been solved using both a series and a finite element method. Several variants of the slump test (including "incipient slumping") have been proposed. The end use of the work is to managing an integrated system for dry disposal of mine tailings.

THE MEASUREMENT OF YIELD STRESS OF WAXY CRUDE OILS

Cheng Chang (PhD - in progress, OPRS/MUPS)

The work has focused on providing an understanding of the yielding process of waxy crude oils and the measurement of a true yield stress. Three different measurements have been investigated. Controlled stress, controlled creep and oscillatory tests, were employed in a Carri-Med, controlled stress cone-and-plate rheometer to study the yielding process for a statically cooled waxy crude oil. The results show that the yielding of waxy crude oils includes a significant elastic response followed by creep and then fracture. This is in good agreement with the conclusion made from measurement using the vane technique. Two true yield stresses, the elastic yield stress and the static yield stress, were measured using the three tests. When the prehistory of the samples was strictly controlled good reproducibility was obtained in each of three tests as well as good repeatability. In the controlled stress test, the effects of temperature, cooling rate, holding time and stress loading rate on the measured static yield stress were determined; while in the oscillatory test, the effects of cooling rate and frequency on both the measured elastic yield stress and the measured static yield stress were studied.

AMMONIA REMOVAL FROM SIROFLOC-TREATED SEWAGE USING ZEOLITE FROM AUSTRALIA

Emma Cooney (PhD - in progress, CSIRO)

There are a variety of physico-chemical processes being evaluated for sewage treatment that are very effective at phosphorus removal. However, the ammonia present in sewage passes through these processes unaffected. This project proposes that a high rate adsorption process, based on naturally occurring zeolite, can be used for ammonia removal from treated sewage. The zeolite is fully regenerateable and exhibits ammonia removal rates commensurate with the high rate of the SIROFLOC sewage treatment plant. The regeneration of the zeolite follows either of two paths. A chemical method involves the retrieval of the ammonia-nitrogen from the exhausted zeolite as the key ingredient in the precipitation of magnesium-ammonium-phosphate (MAP), an ideal slow release fertiliser, or the biological oxidation of the ammonia using nitrifying bacteria, resulting in the nitrification (aerobic) followed by the denitrification (anaerobic) of the ammonia in the sewage feed screen. Simultaneous loading and regeneration is being explored as this approach would minimise equipment cost and operating time. The simultaneous removal of soluble BOD, present in the effluent from the SIROFLOC process, is also being investigated.

THE RHEOLOGICAL PROPERTIES AND DE-WATERING OF SLURRIED COAL MINE TAILINGS

Ross DeKretser (PhD - completed, AMPC/ARC)

The presence of montmorillonite clay in coal tailings creates poor rheological and de-watering properties resulting in environmental problems associated with conventional disposal methods. The rheology and de-waterability, measured by a variety of parameters, of samples of real and simulated coal tailings suspensions and suspensions of clay alone has been evaluated in conjunction with modifications on the surface chemistry of the clay in order to improve the handling properties. The results provide a broad picture of the behaviour of clay based tailings, ion exchange and changes in electrolyte concentration and provide specific insights into where a knowledge of the surface chemistry of the clay can be used to produce significant improvements in the de-watering efficiency with implications that are of both financial and environmental importance.

THE EFFECT OF FLUID HYDRODYNAMICS ON DROPLET COALESCENCE

Trina Dreher (PhD - in progress, Melbourne Water Scholarship)

Liquid membrane separation shows promise as an alternative to traditional ion exchange separation techniques. In particular interest has been stimulated by its greater selectivity and lower cost compared to the other separation methods. The major problem which has limited success is the short lifespan and instability of the liquid membrane, which currently makes it unsuitable for commercial use. The research is concerned with the extraction of metal ions from waste solutions using supported and emulsion liquid membranes. Emulsion liquid membranes are water-in-oil-in-water emulsions with the liquid membrane being essentially the oil phase. Coalescence of the internal water phase is the main reason for membrane instability. Therefore the effect of continuous phase rheology on the coalescence rate of water drops is being investigated. Supported liquid membrane expreiments have been performed to determine the effect of varying elasticity and viscosity of the liquid membrane on the operating parameters. It has also been shown that the addition of polymer has no effect on membrane performance due to the low shear rates encountered at the membrane surface. Experiments to determine the coalescence rate of water drops in an organic medium have also been conducted. Results indicate that as the viscosity of the organic continuous phase is increased, the coalescence time increases significantly. The coalescence time also increases significantly with elasticity. It has been found that there is a large variation in coalescence time in contaminated solutions. Using the same fluids as those for the coalescence experiments, the terminal velocity of the falling water drops has been determined. This has enabled the flow regime of the drops to be determined and the level of contamination in the system to be determined qualitatively. Modelling of the drop coalescence and testing of supported and emulsion liquid membrane systems with an industrial waste water is being investigated.

REDUCTIVE DISSOLUTION OF OPTICALLY TRANSPARENT COLLOIDAL CuFeS2

Kate Drummond (PhD - in progress, APA/ARC)

The redox chemistry of the copper sulphide minerals chalcopyrite (CuFeS2) and covellite (CuS) is of interest in this work. These semiconducting minerals have been synthesised as colloidal sols which enables UV-visible spectroscopic detection techniques to be used in analysis of redox processes. Radiolytic techniques are also being applied to study the reductive dissolution of CuFeS2 and CuS by the one electron reductant radical, zwitterionic viologen (ZV-). Corrosion reactions have been proposed for both sulfide mineral systems following the identification of products and the determination of the number of electrons transferred to the colloids during the reduction processes. In addition to a corrosion reaction, it was noted that both colloidal systems act as catalysts for molecular hydrogen generation. The effect of solution pH on the number of electrons transferred to the colloid during reduction has also been studied. Semiconductor energy levels (specifically the conduction band) have been assigned for both CuFeS2 and CuS. and the values were observed to correspond well with the literature. Recent work has focussed on investigating the oxidation of CuS by the one electron oxidant, ferricyanide (FeCN(3-)(6)) using a stop flow system. Insight into the reaction kinetics and stoichiometry of the electron transfer process is being sort.

INTERFACIAL PHENOMENA IN SOLVENT EXTRACTION

Emel Erbasi (BSc(Hons.) - completed)

A study of the kinetics of Cu2+ extraction by the oil soluble complex 7-(4-ethyl-1-methyloctyl) 8-hydroxyquinoline (Kelex 100) was undertaken in a modified static transfer cell. The concentration of the complex formed at the interface was monitored by Attenuated Total Internal Spectroscopy (ATR) as the reaction proceeded. The kinetics of extraction was measured under a variety of conditions and the reaction process was modelled using a short time predictive equation, which gives a complex concentration - time profile. This is expected if the extraction process is diffusion controlled. The diffusion model predicted lower rates and levels of complex formation than observed experimentally. It was found that convection in the oil phase could account for the discrepancy.

THE EFFECT OF RHEOLOGY ON COALESCENCE PHENOMENA IN EMULSION SYSTEMS

Dianna Goodall (PhD - in progress, Aust. Food Industry Science Council)

The quality of some food and industrial products such as sauces, mayonaises, and acrylic paints depends on the stability of the emulsion system. A necessary prerequisite to understand the rheology and stability of such products is an understanding of the properties that effect coalescence. This project involves the development of an "Imaging Ellipsometry" technique to monitor the liquid/liquid interface of droplets as they coalesce. Of interest is the effect of viscous forces on the profiles of droplets as film drainage occurs. The work will investigate both model and complex systems to determine whether the effect of altering the viscosity of the continuous phase is system dependent, or applicable to all emulsions. Film profiles for a simple system of an oil droplet pressed towards a hydrophilic surface in a continuous medium of varying viscosity have obtained. Droplets were observed to acquire a 'dimple' type shape as increased pressure was applied to the droplet. Equilibrium film thicknesses obtained were in good agreement with other workers, hence showing that imaging ellipsometry can be used to study a system of this type.

SULPHURIC ACID RECOVERY FROM COPPER EXTRACTION CIRCUITS

Ken Gottliebsen (M.Eng.Sci. - in progress, APA)

The aim of this project is to develop an extraction process that will enable the recycling of acid from leaching circuits into other parts of the metals refining process. This will reduce the cost of raw materials (acid), reduce the amount of acid effluent and so reduce environmental impact. A reduction in the cost of production of metal from a number of Australia's mines, particularly those in remote locations, is critical to increasing competitiveness. To recover the sulphate from the purged stream of an electrowinning plant, it is proposed to add a second solvent extraction plant to the current copper extraction processle. This could be in the form of either a number of mixer settlers or alternatively a solvent extraction column. This process involves counter current contacting of the bleed liquor with an organic solvent in a number of extraction stages. The extractant selectively extracts the sulphuric acid which is then stripped using water in a number of stripping stages. Ideally this will produce a purified concentrated acid product stream (above 120 g/l). The effect of elevated temperature on the equilibrium will be investigated.

TECHNIQUES FOR THE CHARACTERISATION OF SUSPENSIONS IN SETTLING AND COMPRESSION

Matthew Green (PhD - in progress, APA)

The settling and compressive behaviour of suspension systems is fully defined by two parameters; the hindered settling factor and the compressive yield stress. The hindered settling factor is a measure of the hydrodynamic drag forces experienced by settling particles in a suspension and allows the settling velocity and the time scale for the settling process to be determined. The compressive yield stress is a measure of strength of the suspension network that is undergo strength of the suspension network that is undergoing compression. This is used to determine the maximum concentration achievable for any given compression conditions. These suspension parameters have been determined using a variety of techniques. Two methods using centrifuges have been fully evaluated and a third using a pressure filtration device is currently being studied. The validity of the compression model of Buscall and White will be checked using these techniques. The materials used in the study are aqueous mineral suspension systems of TiO2, Al2O3 and ZrO2. The rheology of these systems is controlled by manipulating the surface chemistry of the particles. Factors used are pH, ionic strength and the use of various polymeric additives. The effect of flocculation and the resulting network structure in the suspension can thus be systematically investigated.

THE PHOTOELECTROCHEMICAL PROPERTIES OF CdS NANOPARTICLES IN LANGMUIR-BLODGETT FILMS

Karen Grieve (PhD - in progress, APA)

The photoelectrochemical (PEC) properties of Q-state semiconductor particles in Langmuir-Blodgett (LB) films are being investigated. Q-state CdS particles of ca. 2nm were initially formed in an LB film and these were progressively grown to ca. 10nm by a series of treatments involving immersion in CdCl2 solution and exposure to H2S vapour. Films containing particles of different sizes were produced in this way. To test the photoelectrochemical properties of the films, they were cast onto an ITO coated glass plate which was used as the photoanode in a PEC cell. The cell also contained a platinum counter electrode, a standard calomel reference electrode (SCE) and an electrolyte solution. The open circuit voltage and short circuit current were then determined in dark and (white) light conditions by cyclic voltammetry, scanning in the range 0 to -1000 mV vs SCE. Previous research has indicated that the LB films may have an insulating effect and inhibit the efficiency of the PEC cell. To overcome this effect, attempts have been made to incorporate the conducting polymer polypyrrole in the films. This was achieved by polymerising pyrrole vapour using AgClO4 as initiator which had previously been introduced to the film. The effects of the polymer on the PEC cell characteristics are currently being examined.

STUDIES IN RANDOM MEDIA

James Gunning (PhD - in progress, APA/AMPC)

The aim of recent work has been on the theoretical formulation of the problem of solid electrode impedances. Attention has been given to the fundamental processes that describe the transient behaviour of the electrical double layer and the ion transport beyond the extent of the double layer. The efficacy of various traditional approximations in the treatment of rough electrodes has been established by comparison to this more fundamental work. Preliminary investigations concerned with the effect of chemical (kinetic) heterogeneity of the surface have been made, and a set of approximations that do not mask the significant effects of heterogeneity have been formulated. This work is important in answering the long debated question of whether the frequency dispersion displayed by the impedance of solid electrodes can be accounted for solely by physical (geometric) considerations.

EFFECT OF POLYELECTROLYTES ON INTERPARTICLE FORCES IN SLUDGES

Peter Harbour (BSc(Hons.) - completed)

An Atomic Force Microscope was used to investigate the effect of polyelectrolytes on the interparticle forces present in a model sludge system. The effect on the rheology (or treatability) of the model sludge was monitored using a vane rheometer to obtain shear yield stress measurements. The polyelectrolytes under investigation were 2k, 90k, 750k and 4000k molecular weight polyacrylic acid, (PAA) and 2000k molecular weight polyacrylamide. The model system was based on a SiO2 suspension. The PAA was shown to act as a dispersant, creating a steric barrier that stabilised the system. The effect was more pronounced for the lower molecular weight polymers. This steric barrier was only observed in AFM studies for the high molecular weight polymers. It was not observed at lower molecular weight due to the size of the interaction being of the order of the surface roughness and/or the adsorption of the polymer being weak. The polyacrylamide was shown to flocculate the system producing an increase in shear yield stress. A small steric barrier was observed in the AFM measurements but the large attraction, expected of polymer bridging, was not observed. The anomaly has been attributed to the differences in the techniques, the AFM providing a dynamic measurement and the vane technique a measurement close to equilibrium.

RECOVERY OF METAL IONS FOR RECYCLING USING HOLLOW FIBRE MEMBRANE EXTRACTION MODULES

Peter Harrington (PhD - in progress, Melbourne Water Scholarship)

The feasibility of using hollow fibre membrane units as liquid-liquid contactors for the removal of metals from waste solutions is being investigated. Liquid extraction is the most selective technique for the separation of individual metal ions from solution, and is used in the mining industry for the separation and purification of metals such as copper and nickel. Its other advantage is that the metal can be easily recovered from the organic phase and so purified ready for reuse, or a specific metal can be removed, such as copper and iron from chromium plating baths leaving the bath free of contamination and so able to be used for a longer period. The exploitation of the technique for recycling of metals has been under-utilised. The relatively low metal ion concentrations found in recycling applications requires that the ratio of aqueous phase to organic phase is high and the existing equipment is not well suited to this phase ratio. The nature of the equipment also requires one phase to be dispersed into the other ensuring some loss of organic in the aqueous phase. This is expensive and can cause downstream problems. It is proposed to use a hollow fibre membrane module to overcome these problems. In this process the solution containing the metal ion to be recovered is passed through the centre of the fibres and the organic phase is passed across the outside of the fibres. In this way the metal ion can permeate the membrane and dissolve into the organic. Because the phases are separated by the membrane there is no emulsion formation and so the loss of organic is minimised. The performance of the equipment is independent of phase ratio and so could potentially be applied to recycling problems. It is proposed to use Kelex 100 (an alky l8 hydroxy quinoline) to investigate a plating liquor.

SONOCHEMICAL COLLOID FORMATION IN AQUEOUS SOLUTION

Rachel Hobson (PhD - in progress, APA)

The formation of gold colloids in aqueous solutions containing tetrachloroauric acid and either alcohol or surfactant molecules exposed to ultrasound has been achieved. Electron microscopy of the colloids has shown that the average particle diameter, as well as the quantity of colloid produced, alters with the different surface active agents in solution. The particle size was found to decrease as the hydrophobicity of the surfactant increased. It is believed that these molecules stabilise the colloid by adsorbing onto the particle surface, hindering further growth. The more hydrophobic the surfactant, the more it will adsorb and therefore the smaller the size of the particles. The primary H radicals produced when aqueous solutions are exposed to ultrasound can attack thiols, producing H2S which can then react with metal ions in solution producing metal sulphide colloids. CdS, PbS, CuS and ZnS colloids have also been produced on the sonication of the metal ion in the presence of a thiol and stabiliser. Particle diameters calculated from the onset of their absorbance spectra show that CdS and PbS colloids produced to be quantum sized.

FORCES BETWEEN HETEROGENEOUS CHARGED SURFACES

Warwick Holt (PhD - in progress, APA)

Surface heterogeneities on colloidal particles may result in nonuniform charge distributions, which result in electrostatic potential profiles that are different from those seen when charge is distributed uniformly. This in turn can give rise to attractive interactions between pairs of such surfaces which may be of greater magnitude and range than van der Waals attractions. Using a geometry involving periodic patches upon a uniform background, investigations have been made into the interactions between heterogeneous plates and spheres. Different combinations of constant potential and constant charge boundary conditions on both patches and background have been simulated. The results show that large attractive free energies can be obtained which are not present in the equivalent uniform surfaces. Furthermore, in the case of pairs of spheres, large restraining torques can be found which maintain the spheres in an attractive orientation.

THE USE OF SURFACTANTS TO ENHANCE THE SELECTIVITY OF SUPERCRITICAL EXTRACTION PROCESSES

Brenda Hutton (PhD - in progress, Aust. Food Industry Science Council)

Supercritical extraction is used for the separation and purification of many essential oils and flavours yet its application for the separation of proteins and other more hydrophilic modules is limited because of poor solubility. The aim of this project is to develop the use of surfactans to form structures such as reverse micelles in supercritical CO2 fluid, which will allow selective solubility of proteins and enzymes which are important food additives and so apply this technology to a much broader range of separation problems in other process engineering streams.

SONOCHRELATIONSHIP BETWEEN SURFACE CHEMISTRY AND FLOCCULANT STRUCTURE OF ASYMMETRIC PARTICLES

Stephen Johnson (PhD - in progress, APA/UWRAA)

The relationship between the surface chemistry, rheology and dewatering properties of both ideal and non-ideal symmetric and asymmetric particle aggregates has been studied. The work has demonstrated strong links between the surface properties and macroscopic suspension behaviour for ideal alumina (symmetric) particle samples. The electrokinetic isoelectric point determined using electroacoustic techniques has been shown to closely correspond with the maximum yield stress calculated during rheological studies. Use of low molecular weight hydrophilic molecules, such as citrate and lactate, has been shown not only to alter the isoelectric point, but to lower the maximum yield stress dramatically. This latter effect is presumed to operate via a mechanism of steric hindrance to interparticle coagulation. Similar studies on kaolinite, proven to be much more complex. Kaolinite studies have been complicated both by difficulty in modelling the edge-edge, face-face and edge-face structural characteristics, which show significant pH dependence, and a unique anomalous surface conductance behaviour.

FORWARD MIXING IN A COUNTER CURRENT SOLVENT EXTRACTION COLUMN

Sandra Kentish (PhD - in progress, APA)

The performance of solvent extraction equipment is dependent upon the distribution of drops that make up the dispersed phase, in particular, the drop size distribution and the extent of forward mixing. At present there is no theoretical description of the dispersed phase, primarily due to lack of fundamental information on drop behaviour. The aim of this project is to develop a probe to extract the dispersed phase droplets rapidly from a column and measure their size using photoelectric sensors and their concentration using spectrophotometry. The data obtained from the measurements are required in the assessment and further development of hydrodynamic mixing models. After extensive experiments on a 75 mm Kuhni column, data have been obtained on the variation of holdup drop size and forward mixing in this column. These data have been used to develop a novel method for identifying the extent of forward mixing and the velocity of individual drop sizes within the column. This has lead to a more realistic model of the performance of these columns and so, more accurate design and scale up will be possible.

SURFACE CHEMISTRY AND RHEOLOGY OF DIVALENT METAL IONS ON OXIDE SURFACES

Deanne Labbett (BSc(Hons.) - completed)

Electrokinetic and rheological experiments were undertaken on silica suspensions. in the presence of Cu(II) and Zn(II). The techniques employed were mobility measurements using an Acoustosizer and shear yield stress measurements using a vane rheometer. It was expected that the dominant forces acting on the system would be van der Waals and electrostatic forces. This was not found to be the case. The deviation from ideality was explained using various other processes that may occur within the system, including surface heterogeneity, complexation and bulk precipitation.

DIRECT FORCES MEASUREMENTS ON METAL OXIDES

Ian Larson (PhD - in progress, APA)

Work has continued with an Atomic Force Microscope measuring the force of interaction between dissimilar metal oxides in aqueous solution. Pure SiO2 spheres (~4*10^-6m diameter) and a-Al2O3 plates are being used in these experimments as there is a large difference in the pH of the point of zero charge, i.e., pure silica has zero charge at pH 2.5 and alumina at pH 4.5. Below these pH values each oxide is positively charged. This difference ensures there is a pH range over which the oxides will be oppositely charged and therefore the interaction force will be an electrostatic attraction. Independent zeta-potential experiments have been made on both materials, microelectrophoresis measurements on the silica colloid sample and streaming potential measurements on the alumina plates. The initial experiments suggest there is good agreement between the potentials measured by the different techniques. DLVO theory accounts adequately for the experimental force-separation profiles. Modelling of the experimental data is best achieved using constant charge rather than constant potential conditions.

THE RHEOLOGY OF TITANIUM DIOXIDE PIGMENT SUSPENSIONS

Petra Liddell (PhD - in progress, AMPC)

Titanium dioxide pigments form the basis of the world’s paint industry. The pigments are produced in an aqueous wet suspension stage before ultimate drying and milling. A knowledge of the rheology of these suspensions is essential for optimum plant operation and in particular ultimate paint production. The rheology of four commercial TiO2 pigment suspensions was investigated as a function of pH, ionic strength, solids concentration, particle size and additives. The rheology was expressed in terms of both the viscosity and the yield stress. The compressional history used for dewatering on the subsequent rheology has been shown to be important.

THE INFLUENCE OF THE MARAGONI EFFECT ON ORGANIC/AQUEOUS PHASE DISPLACEMENT

Paul Lyford (PhD - in progress, APA)

This study has examined the influence of the Marangoni effect on the movement (displacement) of hydrocarbon droplets dispersed in an aqueous phase within a porous medium, with particular reference to its possible application to enhanced oil recovery. Oil displacement was measured in ballotini packed columns with Shellsol or kerosene as the trapped oil. Displacement of the oil was undertaken using water flow containing a variety of solutes. Appreciable oil recovery was observed when Marangoni agents (aliphatic alcohols) where used in the flooding stream that was directed through the porous medium. The maximum effect could be directly matched to the alcohol that, when added to a two phase oil-water system, showed the greatest variation in the interfacial tension with time of the oil/water interface. Interfacial tension was determined using a pendant drop facility specifically constructed to investigate Marangoni effects. A strategy for using the results in real oil bearing rock systemhas been developed.

EFFECTS OF SURFACE CONDUCTION ON THE ELECTROKINETIC TRANSPORT PROPERTIES

C Mangelsdorf (PhD - in progress, APRA)

The theory developed by De Lacey and White [J. Chem. Soc. Faraday Trans. 2, 77, 2007 (1981)] to calculate the electrophoretic mobility of a spherical colloidal particle subjected to an oscillating electric field has been modified to include the inertial terms in the Navier–Stokes and colloidal particle force balance equations. These equations were solved numerically throughout the range of zeta potential, frequency, particle size and electrolyte concentration, and also solved analytically for low zeta potential. The numerical results are compared with the De Lacey and White model, the low zeta potential formula and some of the thin double layer results available. The full electrokinetic theory has also been extended to include specific interactions and lateral movement of ions in the region behind the slipping plane as well as a time varying particle surface charge density. The effects of individual Stern layer parameters, different Stern layer adsorption isotherms and time varying charge densities have been compared with the case when surface conduction is absent.

PHOTOELECTROCHEMICAL PROPERTIES OF "Q-STATE" CdS PARTICLES IN ARACHIDIC ACID LANGMUIR-BLODGETT FILMS

Herman Mansur (PhD - in progress, in conjunction with the School of Engineering, Universidade Federal de Minas Gerais, Brazil)

The photoelectrochemical (PEC) characteristics of thin films of "Q-state" CdS semiconductor particles in arachidic acid Langmuir-Blodgett (LB) layers have been examined. Initially "Q-state" size CdS particles of ca. 2nm were formed in the film and then progressively grown to ca. 10nm by a cyclic sequence, which involves exposing the film to H2S(g) following its immersion in a CdCl2(aq) solution. A PEC cell was constructed using a layered glass/ITO-CdS/LB plate as the photo-anode and a standard calomel electrode (SCE) as the reference electrode. The photoelectrical response of electrodes coated with LB films containing CdS particles of various sizes was investigated using white light. Values for the open-circuit (Voc) and the short-circuit current for the PEC cells were obtained and fill factors in the range 20 to 70-75% were calculated. Voc decreased from ca. -200 to ca. -800 mV vs. SCE with increasing particle size. This effect was attributed to the dielectric properties of the arachidic acid LB film matrix. A more complex particle system has also been investigated involving a core of CdS with a monolayer shell of CdSe. The PEC cell characteristics of this core-shell CdSxSe1-x LB film resembled that of CdSe at large particle sizes of 10 nm. At small sizes, of 2 nm, the particle film behaved similar to the CdS system.

A SURFACE FORCES STUDY OF QUATERNARISED POLY(2-VINYL-PYRIDINE) ADSORBED ONTO MICA

George Maurdev (BSc(Hons.) - completed)

The interaction forces between two macroscopic mica surfaces onto which quaternarized poly-2-vinylpyridine (Q-PVP) had been adsorbed were measured using the Surface Forces Apparatus. In the system containing Q-PVP chloride, interaction forces were measured ranging from a surface separation of 100 nm to a hard wall repulsion at 50 nm, the interaction forces comprising of electrostatic and steric components. In the analogous polyelectrolyte systems with iodide counter ions, repulsive interaction forces were measured from a surface separation of 35 nm, increasing to a hard wall repulsion at 10 nm in the presence of iodide salt. The adsorbed chloride polyelectrolyte salt was shown to exhibit a hard wall repulsion at a larger surface separation than deduced from spectroscopic data. This was attributed to the higher effective charge of the polyelectrolyte as compared to the iodide polyelectrolyte salt, resulting in polymer-polymer repulsive forces.

THE EFFECT OF NON-NEWTONIAN FLUID PARAMETERS ON DROPLET FORMATION

Robert Mun (PhD - in progress, AMPC)

In the study of laminar flow capillary jets has received considerable attention in the literature. This focus is due to the large number of industrial processes in which a liquid is broken into droplets. The laminar flow capillary jet is a system in which the basic fluid mechanics are well understood and this has led to a well developed theory of non-Newtonian fluid properties. Studies into the behaviour of capillary jets formed from polymer solutions have been hampered by the lack of a means to measure any relevant physical properties associated with the presence of the polymer. The experimental requirement of using low viscosity fluids for jet break-up has prevented the use of conventional viscometers to measure any dynamic properties of the test fluids. This limitation has been overcome by the use of molecular theories to predict the unmeasured properties. The work of Goldin et al. [J. Fluid Mech. 38: 689-711 (1969)] and Bousfield et al . [JNNFM, 21: 79-97 (1986)] implied that the presence of viscoelastic properties resulted in an increase in the break-up length of a capillary jet relative to a Newtonian fluid of the same shear viscosity. Bousfield et al.'s theory assumes that there is an initial enhancement of the growth of surface disturbances that then tapers off as the disturbance size grows, causing a retarded break up. The theory is supported by their experimental results. Both experimental studies used polymer in water. Other studies showed the opposite effect whereby the use of PIB in Tetralin caused a reduction in the break-up length. In both cases a Maxwell relaxation time was used to quantify the effect observed, so that the two models are mutually exclusive, predicting opposing results for a given test solution. This raised the question of whether or not there is a fundamental difference between effects induced in organic and aqueous polymer systems. The initial objective of this work was to conduct a systematic study into the behaviour of laminar flow capillary jets of dilute aqueous polymer solutions, where a property relating to the elastic behaviour of the polymer, the extensional viscosity, could be measured and to examine the apparent conflict between previous workers. Our work shows that the behaviour of capillary jets depends upon the concentration of the polymer. This phenomena has only been examined for two flexible polymers. The work was extended to determine if a similar effect could be observed for common agricultural spray systems. Flexible, semi-flexible and rigid polymers exhibited similar behaviour, at different concentrations.

CONFORMATIONS AND INTERACTIONS OF ADSORBED POLYELECTROLYTES

David Neivandt (PhD - in progress, APA)

Adsorption on silicon oxide of a mixed solution of the polyelectrolyte poly(styrenesulphonate) (PSS) and cetyltrimethyl-ammonium bromide (CTAB) surfactant has been studied. The surface excess of the polyelectrolyte was determined by ultra-violet Attenuated Total Reflectance (UV-ATR) monitoring of the 224 nm styrenesulphonate absorbance band. Measurements by infrared Attenuated Total Reflectance (IR-ATR) of the 2920 cm-1 symmetric and 2850 cm-1 asymmetric methylene bands common to both surfactant and polyelectrolyte were made. Deconvolution of the PSS and CTAB contributions to the combined methylene infrared resonances gave the adsorbed amount of surfactant, along with a measure of polyelectrolyte adsorption independent of the UV-ATR experiments. Employing these techniques, the surface excess of both polymer and surfactant were determined in-situ for different pH values and solution histories. It was found that the adsorbed amount of both species was highly dependent on pH and on the order of addiiton of the polyelectrolyte and surfactant. These results are being interpreted in terms of competing interactions between the polyelectrolyte and the surface, the surfactant and the surface and co-operative surfactant/polyelectrolyte interactions. Further IR and UV-ATR experiments are being conducted to determine the adsorbed conformations of both the polyelectrolyte and surfactant.

COMPRESSION AND FLOCCULATION OF BAUXITE RESIDUE SUSPENSIONS

Nick Pashias (PhD - in progress, CRG (Alcoa))

The slump test previously used by civil engineers for determining the flow properties of fresh concrete has been adopted as a means of accurately measuring the yield stress of a flocculated suspension. The slump test offers a quick and easy way of measuring the yield stress without the need for sophisticated electronic equipment, thereby giving plant operators an effective tool for examining yield stress. A simple theoretical model has been developed for predicting the yield stress from the results of the slump test. Experimental results undertaken on various suspensions illustrate good reproducibility and agreement with theoretical predictions. The flow properties of the carbonated Bayer process residue have been investigated and the results indicate that there is a degree of neutralization for which the flow characteristics both in shear and compression are optimised. Experiments on samples obtained from various points throughout the dry disposal process in Western Australia have indicated that the effect of polymer flocculation on compression occuring in the super thickener is to increase the structure of the material.

THE INFLUENCE OF TEMPERATURE ON MULTICOMPONENT ION EXCHANGE PROCESSES

Svetlana Paykin (M.Eng.Sci. - in progress, ARC)

Multicomponent ion exchange equilibria have been examined at different temperatures and a model has been developed to predict the influence of temperature on the equilibria. The model is based on the Pitzer model for activity coefficients in the aqueous phase and the Wilson model for activity coefficients in the resin phase, and enables the prediction of multicomponent distribution of ions in an ion exchange system where the temperature is varying. To date, data are being gathered to compare with the model proposed; this is of particular importance where ion exchange processes are required to extract individual ions from a solution of a mixture and is being applied to debittering pear juice.

GELATION STUDIES ON HYDROXYPROPYLGUAR

David Power (PhD - in progress, APCRC)

Hydroxypropylguar forms a gel through the addition of borate ions to a polymer solution. This gel system is used extensively in the petroleum industry as a hydraulic fracturing fluid. Hydraulic fracturing is a stimulation process for oil/gas wells. The gelling process occurs under high shear conditions, with the magnitude and duration of the shear field affecting the rheological properties of the gel at equilibrium. Little is known of the mechanism of the gelling process and the manner in which the flow field dictates the network structure of the resulting gel. By varying the stoichiometry of the reacting components it is possible to clarify the mechanism of gelation. In combination with dynamic rheological monitoring of the gel reaction, this work has lead to a greater understanding of the process.

AXIAL MIXING AND MAL-DISTRIBUTION IN LIQUID EXTRACTION COLUMNS

Abdul Qader (PhD - in progress, APA)

The design of contactors for liquid extraction processes is based on a one-dimensional fluid model including the extent of axial mixing or back mixing. However, recent work in the scale up from laboratory to large scale diameter columns indicates that a significant maldistribution or radial mixing is important. The aim of this project is to investigate the extent of maldistribution and to develop methods to enable accurate design and scale up of these devices. In particular, continuous phase axial dispersion and maldistribution in pulse perforated plate columns have been measured with a view to determining the effect of column diameter and system physical properties. Extensive work on the measurement of pressure drop and holdup profiles within a 300 mm diameter column has been undertaken and models are being developed for analysis of the results.

RETARDATION PROCESSES IN ELECTROKINETICS

Adrian Russell (PhD - in progress, University of Melbourne Faculty Schoolarship)

Electrokinetic measurements such as electrophoretic mobility and dielectric response are widely used to determine the zeta potential of colloidal particles. Some workers have raised doubts about the standard theories used to interpret these measurements due to discrepancies in the zeta potentials measured using the two techniques. Measurements performed on highly charged sulphonate/polystyrene latices using these two techniques show good agreement with theory. Continued dielectric response measurements have given indications that such discrepancies may be due to experimental problems rather than inadequate theory. Irregularities caused by sample preparation have been observed which may make the technique of dielectric response inappropriate in a number of colloidal systems. Work has commenced on the effect the presence of polymeric "hairs" on electrokinetic measurements. This study, using novel latices, is being undertaken in collaboration with the Science University of Tokyo, Japan. Although in its infancy the study has already yielded significant information about the effects of structured surfaces.

SONOCHEMICAL DISSOLUTION OF MnO2 COLLOIDS

Joe Sostaric (PhD - in progress, MUPS)

When 20 kHz ultrasound is applied to water, a great deal of mechanical agitation is produced, hence its common use in the dispersion of colloidal material in aqueous solution. However, the passage of ultrasound through water also leads to chemical activity arising from the formation of highly reactive hydrogen and hydroxyl radicals, which are produced in high temperatures regions formed due to the collapse of vapour filled cavities in solution during sonication. Thus the effects of ultrasound on aqueous colloidal solutions is of particular importance. Recent work has involved studying the effects of ultrasound on the chemical dissolution of nano sized colloidal CdS particles dispersed in aqueous solutions, including the effects of chemical additives on the dissolution process. The immediate aim of the study is to better understand the chemical processes that lead to the dissolution of colloids in water, and to relate this to the physical processes that lead to the chemical activity observed in solution during sonication.

ELECTRICAL DOUBLE LAYER INTERACTIONS BETWEEN TWO UNEQUAL SPHERES

Jim Stankovich (PhD - in progress, APA)

A number of calculations have been performed on electrical double layer interactions between heterogeneous spherical colloidal particles and between a sphere and a plate using nonlinear Poisson-Boltzmann theory. Numerical calculations of these interactions grew out of previous work looking at identical spheres. Results were compared with the linearized Poisson-Boltzmann equation and Derjaguin approximation. The main conclusion is that the Derjaguin approximation is highly accurate for the force in sphere/plate geometry and acceptably so for dissimilar spheres under typical colloidal conditions. Further work has been performed on modelling adsorption of charged latex particles on mica in conjunction with workers form the University of Delaware. Electrical double layer interactions were calculated to assist in the simulation of adsorption experiments using the algorithm of Random Sequential Adsorption. Finally, electrical double layer interactions between heterogeneous spherical colloidal particles have been examined using linear Poisson-Boltzmann theory. The exact solution presented by Glendinning and Russel [JCIS, 93: 95-104 (1983)] was extended to spheres with non-axisymmetric surface charge distributions.

OBSERVATION OF ELASTIC EFFECTS IN SWIRLING FLOW OF VISCOELASTIC FLUIDS

Jason Stokes (PhD - in progress, APA)

The confined swirling flow apparatus, consisting of a fully enclosed cylinder with a rotating base, was used to examine the effect of elasticity in viscoelastic fluids. Various flow instabilities and phenomena were observed using flexible polymer Boger fluids under various operating conditions. In particular, low viscosity dilute polyacrylamide solutions were used to examine the existence domain of vortex breakdown, which is a phenomenon observed using Newtonian fluids. It was found that the addition of parts per million of polymer to a glycerol-water solvent drastically changed the secondary flow field. Vortex breakdown was observed at much larger Reynolds numbers that when a Newtonian fluid with the same constant viscosity was used due to the elasticity of the polymer solution. Vortex breakdown was also suppressed totally using a 75ppm polyacrylamide solution. Examining the effect of polymer on the existence domain of vortex breakdown in confined swirling flow provides a suitable test case for numerical analysis in the development of constitutive equations in non-Newtonian fluid mechanics.

SPECTROELECTROCHEMISTRY OF COLLOIDAL SILVER

Thearith Ung (BSc(Hons.) - completed)

The spectroelectrochemical response of small silver particles (diameter = 6 nm) was studied in aqueous solution using an optically transparent, thin layer electrode. The position of the surface plasmon band was found to be dependent on the applied electrode potential. A value for the double layer capacitance of 30+/-10 mF cm-2 was obtained, based on the spectral shift. The equilibration kinetics of the particles with the electrode obeyed the Cottrell equation, and the diffusion coefficient of the colloids could be measured from the current-time curves. However, the number of electrons transferred at each particle - electrode encounter was found to be electrode potential dependent, and reached 1200 for large negative potentials.

THE INFLUENCE OF FLUID ELASTICITY ON THE INTERFACIAL STABILITY OF RADIAL TWO PHASE FLOW

Eric Weisser (PhD - in progress, AMPC)

Miscible displacement experiments were performed in a one metre diameter Hele-Shaw cell in order to investigate viscous fingering phenomena. Displacement experiments with Newtonian fluids confirmed the well known dependence between viscous fingering and the viscosity ratio. Further experiments indicated that the onset, and form, of viscous fingering and the characteristic fingers produced were also a function of the Peclet number. The Newtonian results were extended to non shear thinning elastic (Boger) fluids using polyacrylamide and xanthan gum, and shear thinning fluids where phenomenological results established the role of elasticity and shear thinning on the displacement process.

FTIR STUDIES OF SURFACTANT ADSORPTION ONTO OXIDES

David Wilson (BSc(Hons.) - completed)

The adsorption of sodium oleate and potassium ethylxanthate surfactants onto zirconia (ZrO2) and titania (TiO2) particles has been investigated over the pH range 3 – 12 using dry state DRIFT spectroscopy. It was discovered that a zirconium oleate complex precipitates onto the ZrO2 particle surface at a high oleate concentration at pH 12. This does not occur in the case of TiO2. At pH 9 this precipitation was not observed but oleic acid and oleate were found to adsorb onto ZrO2. This demonstrates that the adsorption driving force is sufficient to overcome any electrostatic repulsion between the surface and the surfactant head group at this pH. Adsorption at pHs 6 and 3 of oleic acid and oleate was also observed. Adsorption of oleate onto TiO2 was measured at pH 9. Potassium ethylxanthate was shown to adsorb onto ZrO2 over the entire pH range of 3-12 whereas no adsorption was detected on the TiO2 surface.

MIXED BOUNDARY VALUE PROBLEMS AND THEIR APPLICATIONS

Michael Yudin (PhD - completed, APA)

This work involves the main approaches to the solution of mixed boundary value problem in potential theory and their applications in continuum mechanics, with particular emphasis on problems in which some parts of the surfaces are subject to deformation-dependent surface forces. The work includes a comparison of different methods of the solution of mixed boundary value problems. A theoretical discussion of the applicability of the mathematical apparatus to generalised rather than to ordinary functions in the case of Flamant’s problem of elasticity in two dimensions has been considered. Short-range distance-dependent surface interactions and the concept of surface energy was then considered.The model of peeling demonstrates that the complicated phenomenon of surface interaction may be described by a simplified model of energy release, although the constant in this model should not necessarily be identified as the usual surface energy. In the case of a peeling experiment this constant is almost twice the thermodynamic surface energy. The developed model of surface interaction was then applied to the description of propagation of cracks. Models of brittle and ductile cracks and for two interacting brittle cracks was considered. It has been demonstrated that for a brittle crack, the simple model of energy release with the parameter equal to thermodynamic surface energy may be used. Some estimates for stress in the vicinity of a top of a crack are made; the criterion for propagation of microcracks in the vicinity of a macroscopic crack is presented. A criterion for the character of fracture (brittle or ductile) is proposed. For a ductile crack, different criteria of fracture are compared. The theories of strong and weak interaction between surfaces was then compared. In the case of a weak interaction, a criterion of equilibrium which does not depend on the details of a force law is presented. In the case of strong interaction, the model of Johnson, Kendall and Roberts, with the energy release constant equal to thermodynamic surface energy, is appropriate. Finally the model was applied to solid-liquid-solid contact. Numerical calculations and some analytical estimates for deformation and stress distribution were considered. The results are discussed in application to modelling of the indentation of an elastic-plastic solid and the sintering of granular materials.

ELECTROPHORESIS OF PROTEINS THROUGH MEMBRANES

Huiping Zhang (PhD - in progress, OPRS/MUPS)

The electrophoretic mobility of Bovine serum albumin, haemoglobin and lyzozyme in large membrane pore has been investigated experimentally. The results for serum albumin and haemoglobin have been compared with the mobility in free solution which was measured using electrophoresis. Both show good agreement. The result for lysozyme matched the literature data which shows that when the size of protein was small relative to the pore size, the membrane would have no effect on the protein migration rates. Tests using a small pore size membrane showed that the mobility of the protein was significantly reduced when the pore radius approached the protein radius. This phenomenon has been modelled in terms of electrokinetic theory using a method of reflection, at the same time taking into account the effect of back flow. Theory agreed with experimental results extremely well. In addition the ionic strength of the buffer and the effect of protein concentration on protein mobility in free solution have been studied. The results show that the protein concentration did effect protein mobility. This effect was not due to hydrodynamic and electrokinetic interaction between proteins, but the protein contribution to the ionic strength.

THE RHEOLOGY AND PROCESSING OF METAL OXIDE SUSPENSION SYSTEMS

Zhongwu Zhou (PhD - in progress, MUPS)

Metal oxide particulate fluid systems were constructed to develop a maximum density minimum viscosity fluid. Such materials have potential utility in coal analysis, in the diamond industry and in other heavy media separation processes. The basic knowledge developed in fundamental research on the inter-relationships between surface chemistry and rheology is exploited in the development of such fluid system. Basic rheological property measurements are made for materials that have been sterically stabilised and where the particle size distribution has been carefully controlled to obtain suspensions of high density and low viscosity.

RHEOLOGY AND AXISYMMETRIC ENTRY FLOW OF DILUTE AND SEMI-DILUTE SOLUTIONS OF SEMI-RIGID MOLECULES

Mark Zirnsak (PhD - completed, APA)

Dilute and semi-dilute solutions of semi-rigid molecules were investigated to ascertain the influence of molecular flexibility on rheology and axisymmetric entry flow behaviour of polymer solutions. Links were established between the observed rheological properties and entry flow behaviour and the predictions of molecular and continuum theories. The semi-rigid molecules investigated were carboxymethyl cellulose and the extracellular polysaccharide xanthan gum. The steady shear rheological properties of the xanthan gum solutions were found to be very similar to those of suspensions of flexible macroscopic fibres while the linear viscoelastic properties were closer to those expected for dilute solutions of flexible molecules. The solutions of carboxymethyl cellulose showed a greater influence of flexibility on the rheological properties than for the xanthan gum solutions. The xanthan gum solutions showed entry flow behaviour very similar to that of semi-dilute suspensions of rigid fibres while the entry flow behaviour of carboxymethyl cellulose solutions was between that of rigid fibres suspensions and dilute flexible polymer solutions. Independent extensional viscosity measurements performed on a xanthan gum solution matched predictions for the extensional viscosity of dilute suspensions of rigid cylinders. Excellent agreement was observed between secondary flow vortex sizes predicted from the extensional viscosity of the xanthan gum solutions and those observed experimentally.