The studies of the dynamics, phase behavior, interparticle interactions, and hydrodynamics of stimuli-responsive pNIPAm-co-AAc microgels were described in this thesis. Due to their responsiveness to external stimuli, these colloidal particles serve as excellent model systems to probe the relationship between colloidal interactions and phase behavior. As a first step, we established our core experimental methodology, by demonstrating that particle tracking video microscopy is an effective technique to quantify various parameters in colloidal systems. Then we used the technique in combination with a microfluidic device that provides in situ control over sample pH to probe the phase behavior of pNIPAm-co-AAc microgel suspensions. In essence, the experimental set-up enables changes in effective particle volume fractions by changing pH, which can be used to construct the phase diagram. In order to explain the unique features of the microgel phase diagram, we measured the underlying pairwise interparticle potential of pNIPAm-co-AAc microgels directly in quasi-2D suspension and proved that the interactions are pH dependent and can range from weakly attractive to soft repulsive. Finally, the hindered Brownian diffusion due of colloidal particles confined by hard walls was investigated systematically and striking differences between hard sphere and soft sphere were found, with soft pNIPAm-co-AAc microgels showing surprising mobility even under strong confinement.

In order to study suspensions of deformable particles, a hybrid numerical technique was developed that combined a lattice-Boltzmann (LB) fluid solver with a finite element (FE) solid-phase solver. The LB method accurately recovered Navier-Stokes hydrodynamics, while the linear FE method accurately modeled deformation of fluid-filled elastic capsules for moderate levels of deformation. The LB/FE technique was extended using the Message Passing Interface (MPI) to allow scalable simulations on leading-class distributed memory supercomputers. An extensive series of validations were conducted using model problems, and the LB/FE method was found to accurately capture proper capsule dynamics and fluid hydrodynamics. The dilute-limit rheology was studied, and the individual normal stresses were accurately measured. An extension to the analytical theory for viscoelastic spheres [R. Roscoe. J. Fluid Mech., 28(02):273-93, 1967] was proposed that included the isotropic pressure disturbance. Single-body deformation was found to have a small negative (tensile) effect on the particle pressure. Next, the rheology and microstructure of dense suspensions of elastic capsules were probed in detail. As elastic deformation was introduced to the capsules, the rheology exhibited rapid changes. Moderate amounts of shear thinning were observed, and the first normal stress difference showed a rapid increase from a negative value for the rigid case, to a positive value for moderate levels of deformation. The particle pressure also demonstrated a decrease in compressive stresses as deformation increased. The corresponding changes in microstructure were quantified. Changes in particle self-diffusivity were also noted.

The goal of this thesis is to study the role of single particle elasticity in the overall behavior of particulate systems. For this purpose, we use microgel particles, which are crosslinked polymer networks immersed in a solvent. In these systems, the amount of cross-linker determines their elasticity and ultimately the stiffness of the particle. For a system of hard spheres, the phase behavior is solely determined by the volume fraction occupied by the particles. Based on the volume fraction, liquid, crystal and glassy phases are observed. Interestingly, microgel particles display a richer and fascinating set of different behaviors depending on the particle stiffness. Previous results obtained in our group show that for highly cross-linked microgels, the glass phase disappears and there are only liquid and crystalline phases. By contrast, preliminary measurements indicate that for ultrasoft microgel particles the system does not show any signature of crystalline or glassy phases. The system seems to remain liquid irrespective of volume fractions. In this Thesis, we will address this striking result using light scattering as well as rheology, in order to access both static and dynamic properties in a wide range of length and time scales. In addition, we will also perform additional studies using very stiff microgels and use their swelling capabilities to change the volume fraction. We will use hydrostatic pressure to change the miscibility of the polymer network and thus change the microgel size; the use of this external variable allows fast equilibration times and homogeneous changes throughout the sample. By using neutron scattering techniques, we study the structural and dynamical properties of the system in its different phases involved.

The dynamics of fiber orientation is of great interest for efforts to predict the microstructure and material properties of a suspension flow system. In this research a fiber-level, hybrid simulation method, LBM‒EBF (coupled lattice‒Boltzmann method with the external boundary force method) is undertaken to advance the current understanding of the hydrodynamic interaction induced rotational diffusion mechanism for rigid fibers in semidilute suspension of low Reynolds number flow. The LBM‒EBF simulations correctly predict the orbit constant distribution of fibers in a sheared semidilute suspension flow. It is demonstrated that an anisotropic, weak rotary diffusion model can fit the orbit constant distribution very well, but it can not describe the asymmetry in Stokes flow observed in semidilute suspension. The rotational diffusion process is then characterized with a three dimensional spatial tensor representation of the rotational diffusivity. A scalar measure of the rotational diffusion‒'scalar Folgar‒Tucker constant', C[subscript I], is extracted from this tensor. The study provides substantial numerical evidence that the range of C[subscript I] (0.0038 to 0.0165) obtained by Folgar&Tucker (J. reinf. plast. and comp, v.3, 1984) in a semidilute regime is overly diffusive, and that the correct magnitude is of O(10⁻⁴). The study reveals that the interactions among fibers become more frequent with either the decrease of fiber aspect-ratio, r[subscript p] (keeping nL³ constant, where n is the fiber number density, and L is the fiber length) or with the increase of nL³ (keeping r[subscript p] constant) in the semidilute regime, which in consequence causes an increase in C[subscript I]. The rheological properties of sheared semidilute suspension are also computed with direct LBM‒EBF simulations. The LBM‒EBF investigation is extended to characterize the fiber orientation in a linearly contracting channel similar to a paper machine 'headbox'. It is found that the rotational diffusion is the predominant term over the strain rate in the semidilute regime for a low Reynolds number flow, and it results in a decreasing trend of rotational Peclet number, Pe, along the contraction centerline. Lastly, in order to improve the numerical consistency of the existing LBM‒EBF approach, a modification to the body force term in the LB equation is suggested, which can recover the exact macroscopic hydrodynamics from the mesoscale.

This study elucidates the effect of various processing parameters on polyacrylonitrile (PAN) /carbon nanotube (CNT) composite fiber structure and properties. Interaction between PAN and MWNT enabled the gel-spun PAN/MWNT composite fiber to be drawn to a higher draw ratio, than the control PAN fiber, resulting in the composite fiber tensile strength value as high as 1.3 GPa. PAN/MWNT composite fibers were stabilized and carbonized, and the resulting fibers have been characterized for their structure and properties. The effect of precursor fiber shelf-time on the mechanical properties of the gel-spun PAN/MWNT composite fibers is also reported. A rheological study of PAN-co-MAA/few wall nanotube (FWNT) composite solution has been conducted. At low shear rates, the network of FWNTs contributes to elastic response, resulting in higher viscosity and storage modulus for the composite solution as compared to the control solution. On the other hand, at high shear rates, the network of FWNTs can be broken, resulting in lower viscosity for the composite solution than that for the control solution. Larger PAN crystal size (~16.2 nm) and enhanced mechanical properties are observed when the fiber was drawn at room temperature (cold-drawing) prior to being drawn at elevated temperature (~ 165 °C; hot-drawing). Azimuthal scan of wide angle X-ray diffraction (WAXD) and Raman G-band intensities were used for the evaluation of Herman's orientation factor for PAN crystal (fPAN) and FWNT (fFWNT), respectively. Significantly higher nanotube orientation was observed than PAN orientation at an early stage of fiber processing (i.e during spinning, cold-drawing). Differential scanning calorimetry (DSC) revealed that PAN-co-MAA fiber can be converted into cyclic structure at milder conditions than those for PAN. Continuous in-line stabilization, carbonization, and characterization of the resulting carbon fibers were carried out. Rheological and fiber spinning studies have also been carried out on PAN-co-MAA/VGCNF (vapor grown carbon nano fiber). The diameter of PAN-co-MAA/VGCNF composite fiber is smaller than that of the PAN-co-MAA control fiber with same draw ratio due to the suppressed die-swell in the presence of VGCNF. The mechanical properties of PAN-co-MAA control and PAN-co-MAA/VGCNF composite fibers were characterized. Crystalline structure and morphology of the solution-spun PAN-co-MAA/VGCNF fibers are characterized using WAXD and scanning electron microscopy (SEM), respectively. The volume fraction of PAN-CNT interphase in PAN matrix has been calculated to illustrate the impact of CNTs on structural change in PAN matrix, when ordered PAN molecules are developed in the vicinity of CNTs during fiber processing. The effect of PAN-CNT interphase thickness, CNT diameter, and mass density of CNT on volume fraction of PAN-CNT interphase has been explored.

Die Arbeit befasst sich mit der Untersuchung des Kernformstofffließens als nichtnewtonsche Fluidströmung. Dazu werden verschiedene Formgrundstoffe und Kernformstoffe rheologisch untersucht. Als Bindersysteme kommen PUR Coldbox und Wasserglas zum Einsatz. Für diese Untersuchungen wird ein eigens für diesen Zweck entwickeltes Messgerät verwendet. Die gewonnenen Daten werden in ein numerisches Modell implementiert, welches mit den Methoden der numerischen Strömungsmechanik den Kernschießvorgang abbildet. Dabei kommt der Open Source CFD Code OpenFOAM zum Einsatz. Der Kernschießvorgang wird mit verschiedenen Kernkastengeometrien numerisch und experimentell untersucht und die Ergebnisse verglichen. Die Ergebnisse der rheologischen Untersuchungen zeigen deutlich den Einfluss der Beschaffenheit des Formgrundstoffes und des Bindersystems auf die Fließfähigkeit des Kernformstoffes. Der Vergleich zwischen Experiment und Simulation zeigt gute Übereinstimmung. Das formulierte Modell gibt die Möglichkeit, Probleme in der Kernqualität vorherzusagen.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1960. / Includes bibliographical references (p. 164-165).

Rheological properties of idealised models which exhibit all the non-Newtonian flow phenomenology commonly seen in dense suspensions are investigated by particulate-dynamics computer-simulations. The objectives of these investigations are: (i) to establish the origins of various aspects of dense suspension rheology such as shear-thinning, shear thickening and dilatancy; (ii) to elucidate the different regions of a typical dense suspension rheogram by examining underlying structures and shear induced anisotropies in kinetic energy, diffusivity and pressure; (iii) to investigate the scaling of the simplest idealised model suspension; i.e. the hard-sphere model in Newtonian media and its relationship to the isokinetic flow curves obtained through non-equilibrium molecular dynamics (NEMD) simulations; (iv) to preliminarily determine the effect of perturbations present in all real colloidal suspensions, namely particle size polydispersity and a slight 'softness' of the interparticle potential. Non-equilibrium isokinetic simulations have been performed upon ;systems of particles interacting through the classical hard-sphere potential and a perturbation thereof, in which the hard-core is surrounded by a 'slightly soft' repulsive skin. The decision to base the present work upon isokinetic studies was made in order to obtain a better under- standing of suspension rheology by making a direct connection with previous NEMD studies of thermal systemst(93). These studies have shown that the non-linear behaviour exhibited by these systems under shear is atttributable to a shear-induced perturbation of the equilibrium phase behaviour. The present study shows this behaviour to correspond to the high shear region of the generalised suspension flow curve.

Many concentrated paste-like materials are composed of deformable particles randomly packed into a dense suspension. Examples of the constituent soft particles include polyelectrolyte microgels, emulsion droplets, polymer coated colloids, and star polymers. These materials share in common many properties such as yield stress, shear thinning, non-zero normal stresses, wall-slip, shear-banding, memory and aging (similar to that in structural, spin and polymer glasses). Their unique properties make soft particle pastes (SPPs) scientifically interesting and extremely useful in industrial applications (as rheological modifiers). In this dissertation particle simulations, theoretical models and experiments are used to study the flow dynamics and rheological behavior of SPPs near confining surfaces - wall-slip and shear flow, and in the bulk - elasticity at small stresses and the non-linear shear rheology. In the study of slip near smooth surfaces, rheological measurements are shown that identify the influence of the chemical nature of the shearing boundary on slip at the shearing boundary. A modified elastohydrodynamic model is presented that incorporates attractive and repulsive short range interactions between the paste particles and captures the corresponding suppression and promotion of slip at the wall. Further, fluorescence microscopy and particle tracking velocimetry is used to visualize slip and flow of pastes near smooth boundaries and study the sensitivity of the bulk flow profile to the nature of the shearing surface. In the study of elastic properties of pastes, SPPs are modeled as three-dimensional systems of randomly packed elastic spheres. Simulations are performed wherein the packing is subject to small deformations to compute the high- and low-frequency shear moduli. The simulation results are compared with the data from experiments on microgel pastes. This model is extended to study paste dynamics under simple shear with added pairwise elastohydrodynamic lubrication interactions between the densely packed soft particles. The shear and normal stress differences generated during simple hear flow are calculated that compare well with the experimental data. In addition, the pair distribution function of the initial isotropic configuration, the elastically deformed and the steady sheared configurations is investigated. A semi-empirical analysis of the microstructure and its evolution due to shearing is presented. / text

Slurry wall is a geotechnical engineering application to control the migration of contaminants by retarding groundwater flow. Sand-bentonite slurry walls are commonly used as levees and containment liners. The performance of bentonite slurry in sand-bentonite slurry walls was investigated by studying the rheological properties of bentonite suspensions, the penetration length of bentonite slurry into clean sand, and stability of the trench under in-situ hydraulic gradients. In this study, the rheological parameters of bentonite suspensions were measured at various bentonite fractions by weight from 6 to 12% with 0-3% of sodium pyrophosphate; an ionic additive to control the rheological properties of the bentonite slurries. The penetrability of the bentonite slurries through Ottawa sand was studied by injecting the slurries into sand columns at different bentonite fractions. The injection tests were performed with the permeameters having different diameters to eliminate any bias on test results due to the different size of permeameter. An empirical correlation for predicting the penetration length of bentonite slurry based on apparent viscosity, yield stress, effective particle size, relative density, and injection pressures was updated by taking into account the effects of the permeameter diameter size. Moreover, the stability of sand-bentonite slurry walls was inspected by studying the hydraulic performance of sand permeated with bentonite suspensions under increasing hydraulic gradients. The critical hydraulic gradient at which washing out of bentonite suspensions is initiated was examined. For specimens with bentonite contents less than the threshold value, the flow occurred through the sand voids and minimal washing out occurred. On the other hand, when the bentonite content was high enough to fill up all the void space between the sand particles, the flow was controlled by the clay void ratio. In this case, washing out did occur with increasing gradients accompanied by an increase in hydraulic conductivity. Accordingly, a relation between the yield stress of bentonite suspensions and the critical hydraulic conductivity was developed. / text