No description available.

No description available.

No description available.

No description available.

The phase behaviour, rheological effects and interfacial properties of binary and ternary liquid mixtures have been studied near critical points. In particular, measurements have been made of the viscosity-at the bulk macroscopic level by capillary viscometry and at the microscopic level by fluorescence depolarisatiorr-and of critical-point wetting and adsorptiorr-at the solid-liquid interface using evanescent-wave-generated fluorescence spectroscopy and at the liquid-vapour interface using specular neutron reflection. The systems investigated have been mostly alkane + perfluoroalkane mixtures or 2-butoxyethanol + H20 or D20 mixtures, although in some cases hexamethyldisiloxane, propanenitrile and perfluorooctyloctane have also been the components of mixtures. The main outcomes of this study are: • Macroscopic viscosity: The divergence to infinity in the shear viscosity of hexane + perfluorohexane at the critical endpoint for approach along the path of constant critical composition both from the single phase and along both limbs of the coexistence curve is described well using the Renormalisation Group Theory critical exponent y = 0.04. The correlation length amplitude obtained by fitting the sheargradient dependence of the viscosity is ~o = (S.S±l.S) A. • Microscopic viscosity: The product of the rotational correlation time and the temperature 'tR"T, often taken as a measure of the microscopic viscosity, exhibits an anomaly as the critical point is approached as a function of temperature. This anomaly mirrors that in the macroscopic viscosity for some fluorescent dye probes, but for others the anomaly is in the opposite sense indicating that other effects such as solvent structure must playa part in the near-critical behaviour of'tR·T. • Critical-point wetting at the solid-liquid interface: The wetting transition temperature has been identified for heptane + perfluorohexane at the quartz-liquid interface from fluorescence lifetime measurements of a probe. The wetting layer is of the same composition as the bulk heptane-rich phase and the transition is tentatively identified as first-order. • Adsorption and wetting at the liquid-vapour interface: The surface structure of several mixtures has been determined by neutron reflection. The results are in general agreement with the expectations of critical-point wetting and adsorption. The surface is complex and in some mixtures an oscillatory scattering length density profile through the interface is required to model the reflectivity data. • Ternary mixtures: The phase behaviour of three mixtures exhibiting tunnel phase behaviour has been studied experimentally and various characteristics of the shape of the twmel identified. A theoretical study on one of the mixtures predicts the drop in temperature for the locus of maximum phase separation temperatures which is observed experimentally.

We use molecular dynamics to simulate the rapid directional solidification of binary alloy solid-liquid interface in the non-equilibrium state. In the pulling fixed velocities, we report the temperature, density, and diffusion coefficient of the interface. In cooling fast, controlling the velocities of solidification for the important parameter of this text¡Ait produces different changes that velocity value will be affected by atom potential energy and system temperature and density¡Athough the system is pulling a fixed velocities, that the speed of every atom of the system is all not constant .The velocity will be changed into the driving force that the solute will be separated and trapped. In the segregation regime, we recover the exponential form of the concentration profile within the liquid phase. Solute trapping is shown to settle in progressively as V is increased or reduction and our results are in good agreement with the theoretical predictions of Aziz.

Composite materials generally consist of different components which individually exhibit an entirely different material behaviour than within the composite. Here, two immiscible liquids are stabilised with solid particles forming liquid-liquid emulsions. Solid stabilised emulsions, also known as Pickering emulsions, have been thoroughly studied and find application in many industrial sectors. In these emulsions one liquid is generally suspended within the other in the form of droplets. Inspired by computer simulations, it should be possible to create a bicontinuous network of two immiscible liquids also stabilised with jammed particles. This will result in an attractive new material which could find possible industrial applications, for example as microreactors. This potential bicontinuous, interfacially jammed emulsion gel was dubbed bijel. Drawing together knowledge from different disciplines this thesis presents an experimental route to bijel formation. Accessing a certain type of phase separation called spinodal decomposition can be used to create a convoluted arrangement of bicontinuous interfaces. Liquid-liquid interfaces can be stabilised by exploiting the fact that solid particles can be irreversibly trapped at liquidliquid interfaces. Once trapped, the presence of the particles demands a minimum interfacial area between the two liquids. If the particles are jammed against each other this will result in the stabilisation of the liquid-liquid interfaces. To stabilise convoluted, bicontinuous interfaces in this way one type of particles must be able to concurrently stabilise two types of curvatures. Over the last three years it has been shown by several different research groups that this is possible. This thesis examines different types of temperature and pressure quenches on binary liquid systems to reach spinodal decomposition in the presence of particles. At the same time the ability of the particles to collect on the interfaces created during such phase separations is tested. It is found that temperature quenches through the critical point can lead to reproducible bijel formation resulting in the first experimental presentation of bijels. Using confocal microscopy the bijel formation process is studied in detail and properties of this new material are examined. To obtain insight into the behaviour of slowly ageing soft materials xray photon correlation spectroscopy is separately carried out on droplet emulsions.

In this thesis, the adsorption of single-wall carbon nanotubes (SWCNTs) at the liquid/liquid interface, and the subsequent electrochemical investigation of the electrical properties of the adsorbed nanotubes have been studied. Prior to the adsorption of the nanotube, the stability of dispersion of SWCNTs in non-aqueous solvents was assessed by determining the onset of aggregation of the SWCNTs when organic electrolyte was introduced. It was found that electrostatic repulsion between the SWCNTs contributes significantly to the stability of the SWCNTs in non-aqueous solvents. Similar result was also found when the aggregation kinetics of molybdenum disulphide (MoS2) dispersion in non-aqueous media was studied using the same organic electrolyte. The formation of nanomaterial-polymer composites by deliberate electrochemical oxidation of pyrrole and the sonochemical polymerisation of the organic solvent was also studied. Electrolyte addition was shown to be a promising way to separate the 2D material from the sonopolymer.

Materials on the nanoscale have very interesting properties. Hence, they are commonly used for a variety of applications such as drug delivery, bio-imaging and sensing devices. Moreover, coating these particles with other materials forming core@shell or Janus particles can further enhance their properties. However, for the particles to be used in medical and electronic devices, their properties such as size, shape and composition need to be precisely controlled. In this PhD., an emulsification technique was chosen to investigate the synthesis of nanoparticles; it is a simple process, does not require any harsh chemicals or temperature and is fast. Emulsification occurs when two or more immiscible liquids and surfactants are mixed. Here, emulsion droplets were produced using a microfluidic device which allowed for the creation of uniform droplets. These were employed as templates to synthesise and assemble nanomaterials. The main aim of the Ph.D. was to develop a droplet based synthesis process to generate nanoparticles and then assemble them into core@shell particles. This Ph.D., starts by synthesising Fe3O4 nanoparticles (~ 12 nm) and assembling them into microparticles (~ 1µm 2µm) using emulsion droplets as microreactors. By tuning the surfactant, droplet size and evaporation rate of the dispersed phase, microparticles of varying shapes and sizes, such as spherical or crumbled shapes, were produced. When these particles are compared with the commercially available particles, the magnetic content of the in-house particles, or sometimes referred to as Loughborough University Enterprises Ltd. (LUEL), are much higher and more uniform, hence resulting in faster separation when used for extraction of analytes. LUEL particles were supplied as part of commercial collaboration. The use of Pickering emulsions were then explored to create core@shell particles using gold nanoparticles instead of a surfactant to produce gold shells and the addition of pre-synthesised Fe3O4 nanoparticles results in Fe3O4@Au core@shell particles. This is the first time Pickering emulsions were used to produce Fe3O4@Au core@shell particles (~ 1.5 µm) within a microfluidic device. However, the shells were not uniform in thickness. In order to improve the coverage, nanoparticles were synthesised in situ at the droplet interface. By placing the gold chloride (AuCl4-) in the continuous phase and by varying the concentration of the electron donor in hexane droplet, single crystal gold nanoparticles and platelets were formed. The reaction is spontaneous at room temperature, creating gold nanoparticles at the interface of the emulsion droplet. The size and shape of the gold nanoparticles were controlled by varying the concentration of the reactants and the size of the droplets. By adding pre-synthesised particles (Fe3O4 nanoparticles) to the droplet, Au@Fe3O4 core@shell particles were formed with an approximate size of 250 nm. The same concept of forming core@shell particles using gold nanoparticles was further expanded by using other metal ions; palladium and silver. Unlike gold, palladium and silver only formed spherical nanoparticles, no platelets were observed. The addition of preformed iron oxide nanoparticles to the palladium results in core@shell particles. However, in the case of silver, no core@shell particles were formed. The study of the rate of reaction was conducted to understand the details of the mechanism. Overall, the process developed in this Ph.D. study allows for the facile synthesis of core@shell particles in a rapid, high throughput reaction. In the future, it is believed it could be scaled up for commercial purposes.

The adsorbed layer morphology of a series of surfactants under different conditions has been examined primarily using atomic force microscopy (AFM). The morphologies of single and double chained quaternary ammonium surfactants adsorbed to mica have been characterised using AFM at concentrations below the cmc. Mixing these different types of surfactants systematically allowed a detailed examination of the change in adsorbed film curvature from the least curved bilayers through to most curved globules. From this study a novel mesh structure was discovered at curvatures intermediate to bilayers and rods. A mesh was again observed in studies examining the morphology change of adsorbed nonionic surfactant films on silica with variation in temperature. Other surfactant mixtures were also examined including grafting non-adsorbing nonionic surfactants and diblock copolymers into quaternary ammonium surfactant films of different morphologies.