Soils disturbed by strip mining practices may have increased colloid loads moving to groundwater resources, also enhancing the transport of contaminants into our water resources. We hypothesize that contaminant transport within soils following mining is enhanced by colloid mobility. Two sites were chosen for this study, a 30-year old reclaimed strip mine in southwest Virginia and a recently mined area from eastern Kentucky. Intact reclaimed soil monoliths were retrieved from sandstone derived soils in southwestern Virginia. Reclaimed monoliths from eastern Kentucky were recreated in the lab. Intact undisturbed (native) soil monoliths representing the soils before mining were also sampled for comparison. Biosolids were added to an additional reclaimed monolith at a rate of 20 T/acre. Leaching experiments with deionized water at a rate of 1.0 cm/h involved 6 cycles of 8 hours each, giving each monolith at least 2 pore volumes of leaching. Native soil monoliths from Virginia had an average colloid elution of 857 mg over all cycles, reclaimed soil monoliths had an elution of 1460 mg, reclaimed soil monoliths with spoil material had a colloid elution of 76 mg, and when biosolids were amended to reclaimed soil and spoil monoliths, 870 mg colloids were eluted. Native soil monoliths from eastern Kentucky eluted 7269 mg colloids, reclaimed monoliths from eastern Kentucky eluted 10,935 mg colloids, and reclaimed soils with spoil material eluted no colloids. Lime stabilized biosolids enhanced colloid elution due to high pH dispersing material within the monoliths, while spoil materials with high density and salt content reduced colloid elution. Metal loads in solution were mobilized by DOC, particularly in low sulfate environments, while colloid bound metals increased the total metal loads in the order of Pb > Ni > Cu > Cd > Zn > Cr.

<p>Abstract to“Interfacial colloidal particle films andtheir structure formation”; a licentiate thesis, whichwill be presented by Sandra Rödner in Q2, 29 November 2002at 13.00.</p><p>Colloidal particles can be made to organise themselves intoordered arrays. These colloidal structures acquire interestingand useful properties, not only from their constituentmaterials but also from the spontaneous emergence of mesoscopicorder that characterises their internal structure. Orderedarrays of colloidal particles, with lattice constants rangingfrom a few nanometers to a few microns, have potentialapplications as optical computing elements and chemicalsensors, and also has an important influence on the mechanicalproperties and optical appearance of paint films and papercoatings.</p><p>The control of colloidal structure formation starts with theparticle interactions (attractive or repulsive) and colloidaldynamics, which is the topic of this thesis. To enable adetailed understanding of the different factors that controlthe formation of dense 2D colloidal films, a method forstructural characterisation was developed. The degree of orderin the hexagonal close-packed structure, displayed by thecolloidal films, was characterised by the size of ordereddomains and by the distribution of pore sizes. The size ofordered domains was obtained from the pair distributionfunction, and the distribution of pores from a Delaunaytriangulation procedure. These methods are based on theparticle positions in the film, which were determined by lightmicroscopy and processed digital images.</p><p>The two methods were used to study the effect of particleinteractions on the structure of colloidal monoparticulatefilms, formed at the air-liquid interface. The size of theordered domains decreased exponentially with increasing bondstrength, while the pore density increased. The transfer andsubsequent drying of the formed film on a solid substrateinduced structural changes; the capillary forces transformedsmall pores into triangular order while some of the largervoids and cracks increased in size.</p><p>The structural features of colloidal monolayers, formed bydrying a dilute silica suspension on a substrate, wereinvestigated. Addition of small amounts of salt resulted indrastic changes of the particle film structure. The size of theordered domains decreased exponentially with increasing amountsof added salt (0-2.9% NaCl/Silica ratio), with a simultaneousincrease of the concentration of large defects. This suggeststhat loss of colloidal stability and onset of particle adhesionto the substrate inhibit rearrangement and ordering. Theevaporation rate was controlled by varying the relativehumidity during drying. Colloidal monolayers with the largestordered domains and the lowest concentration of stacking faultswere formed at an intermediate humidity (55% RH).</p><p>The rearrangement process during drying of dilute silicasuspensions was followed in detail by studying the changes inthe structural features during growth of colloidal monolayers.Low crystal growth rate promoted the transition of squarelattice domains to a hexagonal close-packed structure. Additionof salt to the electrostatically stabilised dispersionincreased the formation of square structured regions at thecrystal-suspension interface, due to increasing adhesion to thesubstrate. The loss of colloidal stability inhibited therearrangement process, resulting in higher concentrations ofsquare lattice domains at large distances from the crystal edgecompared to systems without added salt.</p>

No description available.

In this thesis we study the physics of colloidal dispersions in active and passive liquid crystals by computer simulations. Liquid crystals are materials that exhibit long-range orientational order, with characteristics intermediate between the ones of simple, isotropic fluids and the ones of crystalline solids. Active fluids are suspensions of particles that continuously stir their ambient fluid. Like liquid crystals, active fluids undergo phase transitions to orientationally ordered phases. The framework that we apply here to describe them extends hydrodynamic equations for liquid crystals to the active case, in which their constituent particles exert local stresses on the simple fluid in which they are embedded. Studying systems of colloids embedded in these materials can be done with multiple aims. Here we use colloids as probe particles to investigate the rheological properties of active nematics. To do so we apply a constant force to a spherical particle embedded therein and define an effective viscosity, which we determine by measuring the velocity in steady state. We find an important dependence of the effective viscosity on the size of the particle, and a regime characterised by a steady state of negative drag. We also consider collective properties for systems of many colloids and analyse how they are affected by activity. We find that spontaneous flow can either hinder or favour colloidal aggregation, depending mainly on whether a fixed orientation of the liquid crystal is imposed close to the colloidal surface. This remains true independently of the initial condition chosen for the liquid crystal, which only affects the transition to spontaneous flow.

by Wong Ho Man, Bruce. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves [60-61]). / Text in English; abstracts in English and Chinese. / by Wong Ho Man, Bruce. / Acknowledgements --- p.i / Abstract --- p.ii / 摘要 --- p.iii / Table of Contents --- p.iv / List of figures --- p.vi / Chapter Chapter1 --- Introduction --- p.1 / Chapter Chapter 2 --- Fabrication of erbium-doped sol-gel derived silica --- p.4 / Chapter 2.1 --- Introduction to the sol-gel process --- p.4 / Chapter 2.1.1 --- The procedure for silica formation - ´ؤ --- p.7 / Chapter 2.1.2 --- Changes during the sol-gel process --- p.11 / Chapter 2.2 --- Factors affecting the fluorescence --- p.15 / Chapter 2.2.1 --- Clustering of Er3+ ions in the silica samples --- p.15 / Chapter 2.2.2 --- Retention of hydroxyl group OH/absorbed water in silica - --- p.16 / Chapter 2.3 --- The role of Aluminum in dissolving Er3+ ions in Si02 network --- p.18 / Chapter 2.4 --- Thermal dehydroxylation --- p.20 / Chapter 2.5 --- Characterization of the Erbium-doped silica samples --- p.24 / Chapter 2.5.1 --- Absorption spectrum --- p.24 / Chapter 2.5.2 --- "Refractive index, density and microhardness" --- p.29 / Chapter Chapter 3 --- Fluorescence spectroscopy --- p.35 / Chapter 3.1 --- Introduction --- p.35 / Chapter 3.2 --- Experimental set-up --- p.36 / Chapter 3.3 --- "Fluorescence spectrum with variation in Er3+ concentration, Al/Er molar ratio and annealing temperature" --- p.38 / Chapter Chapter 4 --- Decay lifetime measurements of the 4S3/2 energy level --- p.47 / Chapter 4.1 --- Introduction --- p.47 / Chapter 4.2 --- Experimental set-up --- p.48 / Chapter 4.3 --- Increase in decay lifetimes with Aluminum-codoping --- p.49 / Chapter Chapter 5 --- Conclusions and further works --- p.58 / References

For some time it was believed that simple, single - component, fluid phase behaviour was limited to a homogeneous gas and homogeneous liquid phase separated by a line of first order phase transitions. However, recent studies have demonstrated that simple fluid behaviour can be extended to richer phase diagrams through tuning of the effective potential. Fluids whose constituent particles feel a strong attraction at close range and weak repulsion at longer ranges have been shown, under certain conditions, to assemble into heterogeneous structures such as spherical and cylindrical clusters, lamellae and spherical and cylindrical voids. Lattice Monte Carlo simulations are used to explore the phase diagram of a single - component fluid following a hard - core effective potential with an attractive and a repulsive Yukawa tail. The relative strngths of attractive and repulsive potentials are found for which heterogeneous structures become stable. Then the region of stability of heterogeneous structures is delimited through the use of histogram reweighting to map out the locus of points at which the homogeneous and heterogeneous states have equal free energy. A transition matrix Monte Carlo biasing technique is used to reveal the system behaviour inside the free energy barrier at low temperatures, when the gas - liquid phase transition appears to have re-asserted itself. Finally, a discussion as to the mechanism for assembly of the heterogeneous structures is offered.

This dissertation presents the results of a series of experimental and numerical studies designed to advance knowledge of the fundamental mechanisms controlling colloidal particle transport in saturated porous media. That colloidal particles facilitate contaminant transport in porous media, or act as contaminant sources, is well known, and also widely recognized as important to environmental and health issues around the world. Many prior and ongoing studies are aimed at understanding particle transport and deposition behavior in saturated porous media, and these studies have generated a broad range of knowledge regarding particle fate and transport mechanisms. However, the prediction of particle transport behavior still remains challenging, not least because the particle transport processes themselves still include many unknown factors. The goal of the work reported in this dissertation, was to advance understanding of the influence of varying flow velocity conditions, flow direction, particle size and mixed particle populations on particle transport processes. In order to meet this goal, a new numerical model for particle transport was developed, and standard laboratory column test protocols were modified to enable the imposition of varying flow conditions during a test, as well as visualization of particle concentrations within the interior of a column. In addition, and in collaboration with other researchers, numerical modeling work was also undertaken to provide insight into the processes governing particle transport at an instrumented field site. Numerical models have been used extensively to investigate a wide variety of engineering and applied science problems, including those involving colloidal particle transport in saturated porous media. For the research presented in this dissertation, a new numerical model, termed the Kinetic Colloid Transport Model (KCTM), was developed and implemented using the Matlab platform. The KCTM is based on a one-dimensional (1-D) advection-dispersion-sorption equation coupled with different kinetic sub-models for simulating particle interactions with the solid phase of a porous medium, including irreversible and reversible attachment mechanisms, as well as two-attachment site and two-particle population behaviors. The KCTM is capable of directly simulating particle transport behavior for a given set of initial and boundary conditions, and also inversely solving for the sub-model kinetic parameters based on particle concentrations observed during column or field experiments. To validate the KCTM, KCTM results were compared with analytical solutions generated by the STANMOD program and numerical solutions generated by HYDRUS-1D. Simulation of particle breakthrough concentrations during a hypothetical column experiment with fourteen different case studies, involving a range of particle dispersion coefficients as well as attachment and detachment rates, was used for the validation. Agreement between the KCTM results and those generated by STANMOD and HYDRUS-1D, as defined by corresponding R squared values (all above 0.999), was considered acceptable across all ten case studies. The KCTM has the advantage of modeling a range of particle transport mechanisms, many of which are not accounted for in current open-source or commercially available codes. Fluctuating or varying velocity conditions are common under many real-world scenarios involving colloidal particle transport, yet are often neglected in laboratory column experiments designed to investigate particle transport behavior. To understand the influence of varying velocity conditions on particle transport, a series of traditional and modified laboratory column experiments was conducted. For the modified column experiments, a protocol was developed to enable the simulation of both increasing and decreasing velocity conditions during a test, as well as conditions involving an increase followed by a decrease in velocity. Laboratory column experiments were performed to examine the downward transport of 2 micron diameter microspheres through a saturated bed of 100 micron diameter glass beads under both constant and varying velocity conditions. The KCTM was simultaneously fit to observed particle concentration breakthrough curves, as well as measured particle concentrations retained in the column at the end of each constant velocity experiment, to obtain a relationship between a dimensionless irreversible kinetic attachment coefficient Ki* and transport velocity. This relationship was then used to model the results of the varying velocity tests, with limited success. A comparison of the Ki* values obtained from direct fitting of the varying velocity tests using the KCTM, with the Ki* values derived from the results of the constant velocity experiments, revealed a potential dependence of Ki* on the rate of change of transport velocity, which is currently not accounted for in any particle transport model. Overall, the results of this experimental and numerical investigation pointed to the need for better understanding of how varying velocity conditions impact fundamental particle transport mechanisms. A visualization technique was used to examine the effects of particle size and flow direction on particle transport in a saturated porous medium comprised of 500μm diameter glass beads. Packed column experiments with uniform (100% 1μm or 100% 6μm) and mixed (90% 1μm with 10% 6μm and 90% 6μm with 10% 1μm) polystyrene latex microspheres were performed in one-dimensional upward, horizontal and downward flow fields at a constant velocity of 1.7m/day. Particle concentrations were recorded over time in the interior of a column and at the column exit. Experimental results showed that upward flow conditions generally gave rise to higher retained particle concentrations and lower particle breakthrough concentrations than horizontal and downward flow conditions, indicating that gravitational settling decreases particle transport distances and enhances particle deposition mechanisms. Consistent with prior studies, results also showed increasing particle retention with increasing particle size. The 1μm particle tests results were successfully modeled using a first order, irreversible particle attachment model, indicating little filtration of this particle size within the glass bead columns during transport. Modeling of the 6μm particle tests required a two-site kinetic modeling approach that accounted for particle interactions with the surfaces of the glass beads as well as straining of particles at bead-bead contact points. The presence of a second particle population had little impact on the transport of the 1μm particles. For the 6μm particles, the presence of the second particle population increased particle attachment rates, with the greatest impact observed during downward flow conditions. Overall, the results of this study confirm that particle size and flow direction impact particle transport processes. The study also reveals that particle size heterogeneity could also impact particle transport under certain conditions. Both of these findings have implications for field-scale modeling of particle transport. The up-scaling of results obtained from laboratory column experiments to predict particle transport at the field scale is generally reported to under-estimate particle transport distances observed in the field. The over-simplification of column experimental conditions, in comparison to field conditions, or the use of improper kinetic models are two possible reasons leading to such inaccurate predictions. In order to explore the possible hurdles to current up-scaling methods, the KCTM was used to analyze a series of Escherichia coli based column experiments using aquifer sand obtained from a field site in Bangladesh, which are described in the collaborative work presented in Appendix A. Four E.coli breakthrough curves (BTCs) and two profiles of spatially retained E.coli concentrations at the end of an experiment were generated by the column test series. The KCTM successfully modeled the BTC results using a two-population kinetic sub-model. Both one-site and two-site particle attachment sub-models failed to reproduce the observed BTCs. None of the kinetic sub-models could reproduce the observed particle retention profiles, although the two-population sub-model generated similar hyper log-linear profiles to those seem in the experiment results. Low mass recovery rates in the column experiments is one possible reason why the KCTM failed to fit the retained profiles. The kinetic parameters obtained from the KCTM fits to the column experimental results were incorporated into a two-dimensional transport model, HYDRUS-2D, to predict E. coli transport observed at an instrumented field in Bangladesh. Predictions obtained using only irreversible attachments kinetics, reversible attachment kinetics and both reversible and irreversible attachment kinetics performed with RMSE values of 1158, 826, and 99, respectively. The dramatic decrease in RMSE with the application of the two-site kinetic model indicates that E. coli transport at the field site likely involves both reversible and irreversible attachment. An important conclusion of this work was the significance of designing laboratory column experiments that can enable the extraction of kinetic parameters relevant to field scale transport processes. The numerical and experimental studies presented in this dissertation examined some factors that influence particle fate and transport in saturated porous media, which are commonly overlooked in many conceptual and numerical models of particle behavior. The results of these studies point to a need to better understand how varying velocity conditions, flow direction, particle size and mixed particle populations influence particle fate and transport. The results of these studies also prompt out several recommended future works. For the developed numerical model, current kinetic sub-models imperfectly reproduced experiment results, also inadequately described the particle transport in microscale observations, indicating the simplified first-order kinetics are inaccurate for describing actual particle transport behaviors. A non-log-linear kinetic sub-model and corresponding micro-scale experiments are needed for better predictions. Moreover, the effects of particle-particle interaction were proven significant in certain conditions, however, the processes is still unclear. Visualization technique introduced in this research is capable to explore the controlling mechanisms in micro-scale and further provides the foundations for developing non-log-linear kinetic model, quantifying the effects of particle-particle interactions, acceleration, and other uncovered physical/chemical factors on particle transport in porous media. Advancing understanding of these factors has potential for improving the prediction of colloidal particle transport under real-world, field conditions, which can benefit many programs aimed at reducing the environmental and health impacts of colloid facilitated contaminant transport.

No description available.

Yam Chi Tong = 懸浮顆粒之介電反應 / 任智堂. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 76-79). / Text in English; abstracts in English and Chinese. / Yam Chi Tong = xuan fu ke li zhi jie dian fan ying / Ren Zhitang. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Spectral Representation of a Pair of Polydisperse Cylinders --- p.3 / Chapter 2.1 --- Introduction --- p.3 / Chapter 2.2 --- Multiple Image Method --- p.4 / Chapter 2.2.1 --- Polydispersity in Size --- p.6 / Chapter 2.2.2 --- Polydispersity in Permittivity --- p.7 / Chapter 2.3 --- Spectral Representation --- p.9 / Chapter 2.3.1 --- Polydisperse Size Cylinders --- p.10 / Chapter 2.3.2 --- Polydisperse Permittivity Cylinders --- p.12 / Chapter 2.4 --- Numerical Results --- p.13 / Chapter 2.4.1 --- Polydispersity in Size --- p.14 / Chapter 2.4.2 --- Polydispersity in Permittivity --- p.17 / Chapter 2.5 --- Conclusion --- p.22 / Chapter 3 --- Dielectric Behaviors of Polydisperse Colloidal Suspensions --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- Dielectric Dispersion Spectral Representation --- p.26 / Chapter 3.3 --- Polydisperse Colloidal Suspensions --- p.28 / Chapter 3.4 --- Numerical Results --- p.30 / Chapter 3.4.1 --- Monodisperse Limit --- p.31 / Chapter 3.4.2 --- Influence of the Medium Conductivities --- p.32 / Chapter 3.4.3 --- Effect of Conductivity Contrasts --- p.34 / Chapter 3.4.4 --- Effect of Varying the Volume Fractions --- p.37 / Chapter 3.5 --- Conclusion --- p.41 / Chapter 4 --- Dielectric Behaviors of Shelled Cell Suspensions --- p.43 / Chapter 4.1 --- Introduction --- p.43 / Chapter 4.2 --- Shelled Spherical Particle Model --- p.46 / Chapter 4.2.1 --- Intrinsic Dispersions --- p.47 / Chapter 4.3 --- Numerical Results --- p.49 / Chapter 4.3.1 --- One Type of Shelled Cells --- p.51 / Chapter 4.3.2 --- Mixture of Two Types of Shelled Cells --- p.60 / Chapter 4.4 --- Conclusion --- p.62 / Chapter 5 --- Dielectric Behaviors of Compositionally Graded Films --- p.64 / Chapter 5.1 --- Introduction --- p.64 / Chapter 5.2 --- Discrete Layer Model --- p.65 / Chapter 5.2.1 --- Linear Profiles --- p.67 / Chapter 5.2.2 --- Gaussian Profiles --- p.67 / Chapter 5.3 --- Continuously Graded Model --- p.68 / Chapter 5.3.1 --- Linear Profiles --- p.68 / Chapter 5.3.2 --- Gaussian Profiles --- p.69 / Chapter 5.4 --- Conclusion --- p.72 / Chapter 6 --- Summary --- p.74 / Bibliography --- p.76 / Chapter A --- The Maxwell-Garnett Approximation --- p.80 / Chapter B --- The Bergman-Milton Spectral Representation --- p.82

Huang Ji Ping. / "1st June, 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 125-134). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.