Doctor of Philosophy, Case Western Reserve University, 2006, Macromolecular Science

Fluidic Systems are present in a variety of fields and applications and multiscaling analysis is an important tool both at the macroscopic scale for the optimization of industrial processes, such as mixing colorants in a polymer matrix or mixing of gases in an engine, as well as at the microscopic level when dealing with microfluidics such as micro-reactors and micro-mixers. In this thesis a multiscaling approach to the analysis of the efficiency of mixing of fluidic systems for multi-component flows is developed and a microstructure characterization based on the concept of multi-fractal behavior is introduced. Generically, mixing is a unit operation that involves manipulating a heterogeneous physical system with the intent to make it more homogeneous. The concept of entropy as the measure of the level of homogeneity of a system is applied and various ways to employ the entropy to characterize the state of mixing in a multi-component system at different scale of observations are explored. Computer simulations of fluidic systems are employed to trace the motion of passive tracers used to visualize the behavior of the fluids and to evaluate the overall mixing efficiency. First the quality of such approach on commonly known systems, such as extruder devices and microchannels, is verified then the use of chaotic advection as a tool to increase mixing efficiency is introduced. To create a time dependence of the flow field, necessary to induce chaotic behavior, a non periodic patterning of one of the walls of the systems is proposed, such that the three components of the velocity field are coupled. The behavior of those chaotic systems is shown to generate interfaces with fractal structures. Since fractal and multi-fractal characteristics can be of great interest in relation with the material properties of the final compound a quantification of this multiscale property is done by calculating the generalized fractal dimensions. There is a certain correspondence between mix (open full item for complete abstract)

Committee: Ica Manas-Zloczower (Advisor) Subjects:

MS, University of Cincinnati, 2024, Engineering and Applied Science: Materials Science

Refractory complex concentrated alloys (RCCAs) are known for their high-temperature mechanical properties, but less attention has been given to their low-temperature thermophysical behavior. High-throughput calculation of phase diagrams (CALPHAD) was used to study the body centered cubic (BCC) phase dominance within the Nbx(MoTi2V4)100-x alloy system by adding Niobium (Nb) at atomic concentrations of x=9%,23%,and 37%, and two additional alloys where vanadium (V) is substituted with hafnium (Hf) and zirconium (Zr) to form Hf10Mo24Nb38Ti28 and Mo24Nb38Ti28Zr10 alloys. Alloys were tested to see the effect of Nb content on the superconducting transition temperature (TC) and the effect of substituting V with Hf or Zr on TC. This approach tests the common assumption of the correlation between VEC with TC, to clarify the role of composition relative to VEC. Button specimens were cast via vacuum arc melting and were measured for electrical resistivity at different temperatures using a Quantum Design DynaCool system. X-ray diffraction (XRD) was used to confirm the formation of the phases predicted by CALPHAD. Five out of the six alloy samples exhibited superconductivity, with some anomalies observed and addressed in this study. These results are compared to literature to enhance understanding of the results.

Committee: Eric Payton Ph.D. (Committee Chair); Matthew Steiner Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, Case Western Reserve University, 2019, Physics

Soft condensed matter is the study of flexible materials that change their shape under the influence of a weak force. Typical examples are polymers and liquid crystals. Chromonic liquid crystals consist of molecules having a hydrophobic flat aromatic core to which have been attached ionic groups or non-ionic groups. These disk-like molecules self-assemble into ordered phases in the presence of solvents, aggregating in a face-to-face fashion, and creating stacked linear molecular aggregates. The degree of self-organization into columns depends on the concentration, temperature, and pressure. Depending on the types of terminal groups, the molecules can be dissolved in organic solvents or water. A theoretical study was performed to model the detailed effects of adding stacking, translation, and rotation energy on the length distribution of chromonic liquid crystals. A second derivative test was done to prove that all the solutions for isotropic phases are at a global minimum of the free energy. The free energies and length distributions for various nematic phase formulations are presented. Free energy and length distribution for both Maier-Saupe and Onsager interactions are presented. The free energy and length distribution for considering I-N phase co-existence and no phase co-existence are presented. It is shown that the nematic phase solutions all lead to a first-order phase transition. The nematic phase solution with the Maier-Saupe interaction causes the averaged aggregate length to increase when the system transitions from the isotropic phase to the nematic phase, while the nematic phase solution with the Onsager interaction causes the averaged aggregate length to decrease. Another major component of this thesis is the study of glass transitions. An analytical study that aims to describe the mean squared displacement at low temperatures is presented. The short-time and long-time limit of the analytical solution are discussed. Then, an app (open full item for complete abstract)

Committee: Philip Taylor (Advisor); Mesfin Tsige (Advisor); Wojbor Woyczynski (Committee Member); Harsh Mathur (Committee Member) Subjects: Mathematics; Physics; Polymers; Statistics