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The morphology and mechanical properties of foams made out of ethylene-α-olefin copolymers (EC) having well-characterized rheological properties were investigated. The polymers differed in the amount of comonomer contained, type of comonomer and molecular weight, resulting in variable thermal properties and different rheological responses under shear and extensional flow. All of the octene-based copolymers with comparable rheological properties had similar foam morphology. However grades with low extensional viscosity and low crystallization points resulted in poor foams. Increasing density resulted in a higher secant modulus of the foamed samples. To further investigate the effects of material properties, trimethylolpropane trimethacrylate (TMPTMA) and triallyl trimesate (TAM) coagents were used to generate a series of PP derivatives through radical mediated melt state reactive modification. Coagent modification resulted in pronounced effects in the molecular weights and viscosities of the derivatives. However, evidence of long-chain branching (LCB) was only present in TAM modified PPs. Significant increases in the crystallization temperature, heat of fusion and crystallization rate were attributed to the formation of nanoparticles, which resulted in a heterogeneous nucleation effect, both for crystallization and foaming. Generally lower viscosities, coupled by strain hardening, enhanced nucleation and increased crystallization temperatures induced by the nanoparticles resulted in foams with higher expansion ratios and smaller cells, due to higher rates of cell growth, coupled with suppressed coalescence. Nanocomposites based on isotactic PP and nanosilica (SiO2) were prepared using a co-rotating twin-screw extruder (TSE) in order to investigate foaming on a larger scale. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good nanosilica dispersion. Well-dispersed surface-modified hydrophobic SiO2 particles were effective nucleating agents for foaming, when used at loadings below 1 phr. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-01-29 14:46:52.042

This work concerns the construction and testing of an optical tweezers-based force transducer, and its application to a hard-sphere colloidal system. A particle in an optical trap forward-scatters a fraction of the trapping light, which is collected in order to give high-resolution information on the trapped particle’s position relative to the trap centre. The system is then calibrated to convert particle displacements to forces. The colloid used in this study is a density- and refractive index-matched suspension of PMMA particles, radius 860 ± 70nm, with volume fractions in the range φ = 40 → 62%. Passive microrheological measurements have yielded information about rearrangements in a tracer’s cage of nearest neighbours, as well as highly localised measurements of the high-frequency viscosity, where the presence of the colloidal host causes around a tenfold increase compared to the bare solvent case. Measurements have also demonstrated the effect of sample history on local short-time self-diffusion coefficient, with perturbations caused by translating a particle within the sample taking up to an hour to relax in a φ = 58% sample. The high resolution particle tracking offered by this technique has also allowed for the first measurement of structure at a shorter lengthscale than the ‘dynamic cage size’ observed using other experimental techniques. In addition, active measurements have shown the emergence of a yield stress on the order of 5Pa as the volume fraction approaches the glass transition at φ ≈ 58%.

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The rapid settling nature of some industrial mineral slurries can cause problems in the measurement of their rheological properties. To address this problem a flow rheometer based on the principles of helical flow was developed. The rheometer designed, is a modified Couette flow system, whereby slurries are circulated through the concentric cylinders by the addition of an axial flow. The purpose of this axial flow is to prevent particles from settling and to maintain a homogeneous suspension. However, the addition of an axial flow component to Couette flow complicates the analysis procedure for non-Newtonian fluids particularly in wide gap geometries. Thus a specific emphasis in this study was placed on developing a correct analysis procedure for helical flow that eliminated the need for rudimentary calibration procedures. Experimental measurements with different liquids, including those with Newtonian and non-Newtonian flow properties showed good agreement between data obtained from the flow rheometer and data obtained using other standard laboratory instruments. Typical differences between the results from the flow rheometer and results from other laboratory instrument varied between 1-2%, with standard deviations in the flow rheometer data of between 2-4%. The flow properties of several non-Newtonian slow settling slurries were examined using the flow rheometer and also with a specially modified tube rheometer. As with the pure liquid results good agreement was obtained between the results from the flow rheometer and those obtained with the modified tube rheometer. Several rapid settling slurries were examined using the flow rheometer, but due to the rapid settling nature of these slurries they could not be examined with any other laboratory instruments. However, internally consistent results were obtained from different tests with the flow rheometer using different values of axial flow rate. These results demonstrate that the correct data analysis method was developed for the helical flow of non-Newtonian fluids Particle migration is a phenomenon known to affect the results of both rotational and axial flow rheological equipment. Whilst the motion of particles within the helical The University of Adelaide Continuous Flow Rheometry for Settling Slurries flow geometry could not be directly observed, careful examination of the results from several experiments with slurries showed that the effects of particle migration were minimal or non-existent within the flow rheometer. It is presumed that the circulation of the fluid through the geometry minimises the residence time in the geometry, which reduces the likelihood of particle migration. The development of Taylor vortices in a Couette type geometry can cause substantial errors in any rheological measurements. The flow rheometer is based on helical flow, which is a combination of both Couette and axial flow and as such may also suffer from measurement errors if instabilities develop in the flow. A stability criterion for the helical flow of non-Newtonian fluids is therefore required to ensure measurements from the flow rheometer were obtained in the laminar flow region. The stability criterion for laminar Couette flow of a Newtonian fluid was well known, as was the effect of imposing axial flow on Newtonian Couette flow. However, the effect of the rate of acceleration of the inner cylinder and the effect of non-Newtonian fluids on the onset of Taylor vortices was unknown. An increase in the rate of acceleration of the inner cylinder was found to have a destabilising effect on Couette flow. A modified Taylor number was developed for non-Newtonian fluids using the power-law model and was experimentally validated for a range of non-Newtonian fluids. These results were then used to develop a laminar flow stability criterion for rheological measurements of non-Newtonian fluids in the flow rheometer. To test the suitability of the results from the flow rheometer for use in the design and optimisation of process units, the power requirements to turn an impeller in a small baffled mixing vessel were investigated. Good agreement was obtained in the laminar and turbulent flow regions for a variety of Newtonian and non-Newtonian fluids between measured values of impeller power and those predicted using rheological measurements from the flow rheometer. Altering the density of the solid particles in a slurry is known to affect the overall rheological properties of the slurry. However, the effects of changing the liquid density were not so clearly defined and thus several artificial slurries of PMMA (poly-methylmethacrylate) spheres in water/NaCl and water/glycerol solutions were used to investigate this phenomenon. It was found that the slurry rheology was altered by The University of Adelaide Continuous Flow Rheometry for Settling Slurries changes in the suspending liquid density, however, these changes could be entirely attributed to changes in the liquid viscosity associated with the changes in liquid density. To summarise, the work presented in this Thesis provides a fundamental approach for the absolute measurement of the rheological properties of settling slurries, under conditions that more accurately represent those found in actual mineral processing operations. / Thesis (Ph.D.)--School of Chemical Engineering, 2004.