Understanding the properties and stabilities of emulsions

Our knowledge of the behaviour of emulsions and the oil-water interface at the molecular level is relatively sparse when compared to the huge importance of these systems in everyday life. This thesis describes the development of several techniques that have the potential to extend this knowledge further. Ellipsometry is exquisitely sensitive to density variations across a fluid-fluid interface, but the interpretation of the ellipsometric response from the oil-water interface, both in the absence and presence of adsorbed species, is nontrivial. The responses from the interface between simple linear alkanes and water suggest that these interfaces are more complex than the air-water interface. The results are indicative of a "drying layer" and a model based on the hard sphere repulsion of a hydrocarbon surface is developed to explain these results. The conclusions from this study on the pristine oil-water interface are used as a basis for the interpretation of the ellipsometric response of a surfactant monolayer at the oil-water interface. The results suggest that the nonionic hydrocarbon surfactant C(_10)E(_8) forms a disordered monolayer with partially-hydrated headgroups. The structure of this film is largely independent of the nature of the superphase; whether air, hexadecane or triolein. The competitive adsorption of the milk proteins ß-casein and ß -lactoglobulin with C(_10)E(_8) at the hexadecane-water interface is also studied. At low and high concentrations of C(_10)E(_8), the measured ellipticity is indicative of an unperturbed protein and surfactant film, respectively. At intermediate concentrations, the measured ellipticity suggests a mixed surfactant/protein film. Raman spectroscopies deliver considerably more data than ellipsometry, but the difficulties of delivering and collecting light from a buried interface require more sophisticated experimental engineering. An attempt is made to sandwich a 100-nm- thick oil film between water and silica in order to probe the oil-water interface by evanescent wave Raman scattering employing a visible excitation source. Unfortunately this procedure has proved unsuccessful to date. The requirement for a thin oil film can be bypassed if the signal from the adsorbed species is enhanced. The design and construction of an ultra-violet resonance Raman microspectrometer is described to achieve this aim. This instrument also has the potential to probe proteins and peptides adsorbed in lipid bilayers. The commissioning and development of a combined in-situ confocal Raman- tribometer is also presented. This instrument is capable of determining the composition of emulsions under shear within a soft elastohydrodynamic contact, as well as the morphology of the soft, deformed surface and the thickness of the lubricating film

NOVEL TECHNIQUES FOR INVESTIGATING THE PERMEATION PROPERTIES OF ENVIRONMENTALLY-FRIENDLY PAPER COATINGS: The influence of structural anisotropy on fluid permeation in porous media

In this study, we have investigated the effects of structural anisotropy of porous media on the permeation of fluids. The motivation for the work was an increased understanding of the permeation of inks into paper coatings, which often contain platey or needle-like particles, which have been aligned during the coating process. However, the findings are also relevant to other systems, such as the sub-terranean migration of fluids, including pollutants, within shale that contains particles of high aspect ratio. Mineral pigments, comprising mainly of calcium carbonate or clay, are often are applied to the surface of paper to improve optical and printing properties. For a high quality image to be achieved, the coating should have sufficient capillarity to allow the ink film to set within the time-scale of a modern printing press. The permeation of fluids into a range of different coating formulations has been investigated, with its main focus on the following samples: Speswhite and Amazon90 SD, which belong to the Kaolin (day) mineral group, and OpacarbA40 and Albaglos, which belong to the Precipitated Calcium Carbonate (PCC) mineral group. The permeation was measured by five different techniques, including a novel use of the Ink Surface Interaction Tester. The results were modelled using a modified version of the software package ‘Pore-Cor’, which simulated both permeability and capillary absorption of a wetting liquid into porous media containing anisotropic voids, and allowed the effects of anisotropy to be isolated from other closely related pore properties. The model generated a simplified three-dimensional void network having pores with a rectangular cross-section and throats with an elliptic cross-section. From visual inspection of the modelled structures, the effect of anisotropy revealed advance wetting in the narrow features of Speswhite-CL and OpacarbA40-CL. Overall, to gain a clear understanding of the permeation of anisotropic structures both inertia and surface throat density is needed to be included in the Pore-Cor model. Once these factors were applied to the model, it was able to predict the permeation of fluids more successfully than those predicted by the Kozeny and aligned cylinders models. The insights gained from this study have allowed conclusions to be drawn about the nature of fluid permeation; they have therefore opened the way to more sophisticated modelling and the engineering of high performance coating structures.SCA Graphic Research AB, Sundsvall, Swede

International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures

Vol. 2O volume I encontra-se disponível em: http://hdl.handle.net/1822/4341

Proceedings of the International RILEM Conference Materials, Systems and Structures in Civil Engineering segment on Service Life of Cement-Based Materials and Structures

Vol. 1O volume II encontra-se disponível em: http://hdl.handle.net/1822/4390

The effect of extensional flow on shear viscosity

Shear rheology is conventionally studied under pure shearing flows, rather than more realistic mixed flows. Moving parallel surfaces and capillary rheometery are examples of the former, whilst the latter occurs whenever a flow accelerates or decelerates creating an additional component of extension, e.g. on passing through an industrial extrusion die. We postulate and gather supporting evidence that shear rheology is a function of not only shear, but both shear and extension rate, a factor with important consequences for fibre spinning and extrusion operations. The direction, as well as rate, of extensional deformation is important. A novel two-phase flow, planar extension experiment is developed and the surface coatings necessary to control the interface structure identified. Shear viscosity evolution is monitored, in-situ, under extensional flow, by optically measuring shear rates either side of a test fluid – reference fluid interface; issues due to optical refraction are critically addressed. Preliminary evidence is shown for a 1.2wt% 4x10^6 MW PEO solution that parallel (+ve) extensional flow, on the order of 11.5s-1 , causes a reduction in shear viscosity, and perpendicular (-ve) causes an increase in shear viscosity, supporting the hypothesis. A framework for a comparison experiment, with the same shear history but without extension, is presented. As part of this work, design criteria for planar hyperbolic extensional channels are critically assessed. In particular, expanding a hyperbola entrance region would maximise total Hencky strain, yet this region is almost never given rationalised consideration in literature. In this region the basis for the hyperbolic profile breaks down, and a new profiling strategy and channel form are presented, which is found to only differ significantly in this inlet region. A useful design limit of 130 degrees on channel inlet angle is identified. The new profile is compared to a hyperbolic profile through the use of CFD for wall slip flow, and a slight improvement in extension rate uniformity along the centreline found. Deviations are contrasted against assumptions made in the profiling strategy: comments are made with regards the possibility for “internal” shear to occur, and non-uniform extension rates are accordingly found to exist between streamlines in these channels despite the use of full wall slip in the simulations

Early-age thermo-mechanical behaviour of concrete Supercontainers for radwaste disposal

The Belgian concept for the disposal of vitrified high-level waste and spent fuel assemblies is founded on the use of cylindrical concrete Supercontainers. This concept is based on a multiple barrier system where every component has its own specific safety function requirements. It consists of encapsulating the heat-emitting waste in a watertight carbon steel overpack and surrounding it by a cylindrical concrete buffer that will then be disposed in a deep clay layer. Finally, the buffer is sealed with a concrete lid. Th concrete materials provide favourable chemical conditions for the overpack allowing it to confine the radionuclides during the thermal phase. In addition, they also ensure shielding protection during construction and transport. A self-compacting concrete (SCC) and a Traditional Vibrated Concrete (TVC) are bein considered for the choice of the cementious buffer, enclosing the radwaste. The use of SCC will ease considerably the precast process and complies with all other requirements regarding strength, durability, chemical interactions,... A laboratory characterization program, in order to obtain the mechanical and thermal properties of the SCC, and 2.5 D thermal and crack modelling simulations, has been conducted to predict the early-age thermo-mechanical behaviour of the concrete buffer during the different construction stages, i.e. the casing of the buffer, insertion of the high-level waste and closure of the Supercontainer. Also the effect of gamma radiation and elevated temperatures on hardening SCC based mortar and hardened SCC was investigated. Finally, the prediction of the avoidance of through-going cracks in the concrete buffer is ensured by means of simulations, after implementation of the obtained test results, and by means of large scale tests, with temperature measurements, displacement and deformation registrations, for the validation of the simulation results of the early-age behaviour of the Supercontainer