Yes / By means of die drawing technique at rubber-state, effect of the orientation of microstructure on dielectric properties of polypropylene/multi-walled carbon nanotubes nanocomposites (PP/MWCNTs) was emphasized in this work. Viscoelasticity behavior of PP/MWCNTs with MWCNTs weight loadings from 0.25 to 5 wt% and dielectric performance of the stretched PP/MWCNTs under different drawing speeds and drawing ratios were studied for seeking an insight of the influences of dispersion and orientation state of MWCNTs and matrix molecular chains. A viscosity decrease (ca. 30%) of the PP/MWCNTs-0.25wt% melt was obviously observed owing to the free volume effect. Differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) were adopted to detect the orientation structure and the variation of crystal morphology of PP/MWCNTs. Melting plateau regions, which indicated the mixed crystallization morphology for the stretched samples, were found in the DSC patterns instead of a single-peak for the unstretched samples. It was found that the uniaxial stretching process broke the conductive MWCNTs networks and consequently increased the orientation of MWCNTs as well as molecular chains along the tensile force direction, leading to an improvement of the dielectric performance.

This dissertation characterizes the geometry, kinematics, and physical properties of insect internal structures that make up the respiratory and circulatory systems. This characterization is necessary to better understand how these systems function to transport fluids at the microscale, and ultimately, how we might computationally model this flow. Chapter 2 describes the geometry of the insect tracheal system, specifically testing if Murray's law applies to this system using three-dimensional imaging of tracheal tubes. Chapter 3 begins to characterize the physical properties of insect hemolymph, specifically the viscosity and density of hemolymph, using experimental measurements. Because insects are strongly affected by environmental temperature, this chapter also explores how hemolymph viscosity may be affected by temperature. Chapter 4 builds on the results of Chapter 3, exploring the effects of developmental responses to temperature on hemolymph viscosity and properties, as well as performance of the insect using experimental measurements. Finally, Chapter 5 presents a kinematic and structural characterization of the insect heart using a variety of imaging techniques and analyses. / Doctor of Philosophy / Insect physiology and morphology has long been studied by biologists and entomologists, with many of the basic features understood and characterized. The insect circulatory and respiratory systems differ greatly from those of many other organisms. Physically, these systems transport fluids through microscale environments which include a variety of pumps, networks, and other structures that facilitate flow. Functionally, the circulatory and respiratory systems are largely decoupled, unlike in vertebrates. The respiratory system transports air directly to deliver oxygen to tissues, whereas the circulatory system transports various nutrients and other chemicals via hemolymph. With these unique differences, investigation of these major biological transport systems in insects is essential to fully understand their structure and function. This dissertation addresses many of the basic structural and physical properties of the insect respiratory and circulatory systems that are still unknown, despite growing engineering analysis. First, I measured specific geometric features of the insect tracheal network and determined if Murray’s law applies to this system. Second, I quantified the viscosity of insect hemolymph, including in response to temperature. To expand upon this relationship further, I measured hemolymph viscosity, hemolymph composition, and insect performance after temperature acclimation during development. Last, I investigated the morphology and kinematics of the insect heart, using many methods of imaging and analysis to measure structural features of the heart wall, including during function. Hemolymph properties and heart morphology provide the physical basis of flow production within the circulatory system. Understanding flow production within the circulatory system, as well as design features of the respiratory system, are crucial in the construction of mathematical models of both hemolymph and air flow within the insect.

M.S.

The densification and shear viscosity of borosilicate glass (BSG) + silica films on rigid substrates were studied. Optical measurement techniques were devised to determine the shrinkage profiles of the free and constrained films and in-plane stress in the constrained films. These films were prepared from slurries of the powder by tape casting. Sintering was carried out isothermally in a hot stage between 665°C and 775°C. The densification rates of both films were observed to be the same in the early stage of sintering but slowed down in the constrained film during the later stage resulting in a lower density. The activation energies for both free and constrained sintering were found to be 385 ± 10 kJ/mol. In-plane stress measurements in constrained films of the pure glass showed the stress to rapidly rise to a maximum level of 20 kPa during the initial stage of sintering and gradually decreased back to zero during the final stage. Densification rates can be given as a product of mobility and driving pressure. Activation energy determinations did not indicate a change in the densification mechanism such that a change in mobility can be ruled out as the reason for the reduced densification rate in constrained films. The stresses are substantially smaller than the estimated lower limit of the sintering pressure and had no observed effect on the densification of the constrained film during the early stages of sintering. However, the stresses could have prevented a few large pores from shrinking during the early stage of sintering leading to the lower density and larger pores observed in the constrained film after sintering. Shear viscosity determinations were also done using data obtained from the sintering of constrained films. The results showed that the density dependence of the shear viscosity is consistent with other work in sinter-forging experiments. However, the results also indicated that the shear viscosity is strongly dependent on sintering temperature. This can be attributed to the different microstructures that evolved when the films were sintered at different temperatures. / Ph. D.

Dilute solution properties of three difficult-to-analyze macromolecular systems were investigated and clarified. Two were notorious for having highly time-in-solution dependent properties, nitrocellulose and lignin, while the third was an ideal model branched methacrylate polymer with which to examine unanswered questions in polymer hydrodynamic behavior. Gel permeation chromatography with a differential viscosity detector (GPC/DV) was employed to study the dilute solution properties of various polymers, specifically their absolute molecular weight distributions and hydrodynamic behavior. The study was divided into three parts. The first part focused on the time dependent change in molecular weight of nitrocellulose. Samples having 12.58% and 13.5% levels of nitration were investigated in THF and EtOAc. GPC/DV, LALLS, FT-IR and intrinsic viscosity experiments revealed that the materials existed as associated molecules in solution which decreased in molecular weight upon storage to extents dependent on the solvent. The second part was an examination of the hydrodynamic behavior of hydroxypropylated lignins using GPC/LALLS/DV and VPO. These materials were found to increase in molecular weight upon storage in solution due to association. Special precautions had to be taken in running experiments to obtain the correct molecular weights and molecular weight distributions. The last part involved a fundamental study of PMMA-g-PMMA's having similar molecular weights but containing different levels of branching. Variable temperature GPC/LALLS/DV was employed to obtain molecular weight distributions, branching parameters, average chain dimensions and information on the hydrodynamic behavior of these branched systems. Samples containing up to 40% of long chain branching were found to obey the universal calibration analytic scheme of GPC. / Ph. D.

Air may be considered a mixture of diatomic nitrogen and oxygen in which all internal molecular energies including molecular vibration are considered. This leads to an adequate thermodynamic description of air up to dissociation. The thermodynamic and transport properties of this "vibrationally excited" gas are presented and compared with those of a perfect gas (which does not include vibration), and of a dissociating gas in chemical equilibrium. The effects of the vibrationally excited gas on Viscous-Shock-Layer flows are then analyzed and compared for a 7° tangent sphere-cone at zero and five degs angle of attack and at altitudes between 50 and 200 kft. The nose radius is 0.15 ft and the body is 30 nose radii long. The wall temperature and freestream velocity are constant at 2,000 °K and 25,000 ft/sec, respectively. In general, the vibrationally excited gas results are more accurate than perfect gas, and computationally much faster than equilibrium. The vibrationally excited gas also shows potential for use in the nonequilibrium flow regime where the chemical reaction rates are too high for the "stiff" finite-rate equations. This and other areas for additional research are discussed. / M.S.

Yes / Size Exclusion Chromatography is traditionally carried out in either aqueous or non-polar solvents. A system to present molar mass distributions of polymers using methanol as a mobile phase is presented. This is shown to be a suitable system for determining the molar mass distributions poly(N-isopropylacrylamide)s (PNIPAM); a polymer class that is often difficult to analyze by size exclusion chromatography. DOSY NMR was used to provide intrinsic viscosity data that was used in conjunction with a viscometric detector to provide absolute calibration. Then the utility of the system was shown by providing the absolute molar mass distributions of dispersed highly branched PNIPAM with biologically functional end groups. / Wellcome Trust

Gutowski et al.'s model has been employed to describe the cure and consolidation of prepregs used for resin film infusion. Resin kinetics, rheology, flow and fiber deformation are considered. Resin kinetics are simulated with an isothermal autocatalytic-1 type relation. The non-Newtonian viscosity of the Cytec™ 754 resin is represented with a gel type expression. The one dimensional flow of resin through a deformable, partially saturated porous medium is studied. A nonlinear partial differential equation describing the spatial and temporal variation of the fiber volume fraction combining the continuity equation, Darcy's Law, and mat compressibility has been derived and solved numerically. Resin is assumed to be incompressible and inertial effects are neglected. Based on the resin content of regions where resin and fiber coexist, expressions for tracking resin flow through fully and partially saturated regions of fiber are given. Values of material parameters for the E-QX 3600-5 glass fabric are estimated from literature data involving compression of similar dry fabrics and through comparison of computed results with the experimental data. Results for the final thickness of the consolidated part agree with the experimental values, but those for the mass loss do not. / Master of Science

The motivation for the determination of the viscosity of polymer solutions in dense fluids at the critical polymer concentration stems from the need to understand the factors that influence the time scale of phase separation in systems that undergo spinodal decomposition upon a pressure quench. In a recent investigation of PDMS + CO₂ and PE + n-pentane where molecular weights of the polymers and the critical polymer concentrations were comparable, significant differences were observed in the time evolution of new phase growth. Among the reasons that contribute to the difference in phase separation kinetics is the viscosity of the solutions. This thesis has been carried out to experimentally demonstrate the differences in viscosities of solutions at their critical polymer concentration. Specifically, the thesis focused on the high-pressure density and viscosity of solutions of poly(dimethylsiloxane) (Mw = 93,700, Mw/Mn = 2.99) in supercritical carbon dioxide and of polyethylene (Mw = 121,000, Mw/Mn = 4.3) in near-critical n-pentane. The measurements have been carried out at the critical polymer concentrations, which is 5.5 wt % for solution of PDMS in CO2 and 5.75 wt % for solution of PE in n-pentane. For PDMS + CO₂ system, the measurements were conducted at 55, 70, 85 and 100 oC and pressures up to 50 MPa. For PE + n-pentane system, the measurements were conducted at 140 and 150 °C and again up to 50 MPa. All measurements were conducted in the one-phase homogenous regions. At these temperatures and pressures, the viscosities were observed to be in the range from 0.14 mPa.s to 0.22 mPa.s for PDMS + CO₂, and from 2.3 mPa.s to 4.6 mPa.s for PE + n-pentane systems. In both systems the viscosities increase with pressure and decrease with temperature. The temperature and pressure dependence could be described by Arrhenius type relationships in terms of flow activation energy (E#) and flow activation volume (V#) parameters. The flow activation energies in PDMS + CO₂ system were about 7 kJ/mol compared to about 18 kJ/mol for the PE + n-pentane system. The activation volumes were in the range 40-64 cm3/mol for PDMS + CO₂ system and 65-75 cm3/mol for the PE + n-pentane solution. The higher values of E# and V# represent the higher sensitivity of viscosity to temperature and pressure changes in the PE + n-pentane system. The viscosity data could also be correlated in terms of density using free-volume based Doolittle type equations. Density is shown to be an effective scaling parameter to describe T/P dependency of viscosity. The closed packed volumes suggested from density correlations were found to be around 0.33 cm³/g for the PDMS and 0.48 cm3/g for the PE systems. Comparison of the viscosity data in these systems with the data on the kinetics of pressure-induced phase separation confirms that the slower kinetics in the PE + n-pentane stems from the higher viscosity in this solution compared to the PDMS + CO₂ system, despite the similarity in the molecular weight of the polymer and the critical polymer concentrations. These viscosity and density measurements were conducted in a special falling-body type viscometer. In the course of this thesis a more reliable procedure for determining the terminal velocity of the falling sinker was implemented. This is based on the precise and more complete description of the position of the sinker with time with the aid of a set of linear variable differential transformers (LVDTs). The design of the new arrangement and procedure for terminal velocity determination and calibration procedures for the viscometer are also presented. The densities and viscosities are determined with an accuracy of ± 1 % and ± 5 % or better, respectively. / Master of Science

Yes / Ice cover formed on a river surface is a common natural phenomenon during winter season in cold high latitude northern regions. For the ice-covered river with compound cross-section, the interaction of the turbulence caused by the ice cover and the channel bed bottom affects the transverse mass and momentum exchange between the main channel and floodplains. In this study, laboratory experiments are performed to investigate the turbulent flow of a compound channel with shore ice covered on the floodplains. Results show that the shore ice resistance restricts the development of the water flow and creates a relatively strong shear layer near the edge of the ice-covered floodplain. The mean streamwise velocity in the main channel and on the ice-covered floodplains shows an opposite variation pattern along with the longitudinal distance and finally reaches the longitudinal uniformity. The mixing layer bounded by the velocity inflection point consists of two layers that evolve downstream to their respective fully developed states. The velocity inflection point and strong transverse shear near the interface in the fully developed profile generate the Kelvin-Helmholtz instability and horizontal coherent vortices. These coherent vortices induce quasi-periodic velocity oscillations, while the dominant frequency of the vortical energy is determined through the power spectral analysis. Subsequently, quadrant analysis is used in ascertaining the mechanism for the lateral momentum exchange, which exhibits the governing contributions of sweeps and ejections within the vortex center. Finally, an eddy viscosity model is presented to investigate the transverse momentum exchange. The presented model is well validated through comparison with measurements, whereas the constants α and β appeared in the model need to be further investigated. / National Natural Science Foundation of China (NSFC). Grant Numbers: 52020105006, 11872285: State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University. Grant Number: 2018HLG01