Engineering Commons^™

Enhancement Of Charge Transfer In Thermally-Expanded And Strain-Stabilized Tips-Pentacene Thin Films, Yang Li

Graduate College Dissertations and Theses

Two of the most critical experimentally accessible properties of small-molecule organic semiconductor materials are the charge carrier mobility, which probes charge transport, and the optical absorption spectrum which probes the energy levels of excited states. The impact of molecular packing on the optical and charge transport properties are often treated separately. However, these effects are actually linked at a fundamental level, and it is of interest to understand the interrelationship between them, as well as how they respond to strain and thermal expansion. In this thesis, we highlight the fundamental relationship between these two phenomena in 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene).

We present …

Experimental And Computational Studies Of Heat Transfer In Flexible Two-Dimensional Woven Fiber Ceramic Materials, Rodrigo Penide Fernandez

Graduate College Dissertations and Theses

Flexible thermal protection materials made from two-dimensional woven ceramics fibers are of significant interest for hypersonic inflatable aerodynamic decelerators being developed by NASA for future missions on Mars and other planets. A key component of the thermal shield is a heat-resistant outer ceramic fabric that must withstand harsh aero-thermal atmospheric entry conditions. However, a predictive understanding of heat conduction processes in complex woven-fiber ceramic materials under deformation is currently lacking. This dissertation presents a combined experimental and computational study of thermal conductivity in alumina-based Nextel-440 and silicon carbide Hi-Nicalon 5-harness-satin woven fabrics, using the hot-disk transient plane source method and …

Exciton Coherence In 1d Phthalocyanine Based Organic Crystalline Thin Films, Kimngan Burrill

Graduate College Dissertations and Theses

Quantum coherence plays a vital role in the excitonic properties of organic semiconductors. Several theoretical and experimental studies have shown an unprecedented role of coherence in charge transfer and transport processes, which in turn can improve the performance of electronic devices. Specifically, an enhancement of exciton coherence size can result in fast energy transport and efficient charge separation. The ability to tailor the design and performance of organic electronics based on exciton coherence effects represents the possibility of ultrafast electronic applications in communication and information technology.

The objective of this thesis is the excitonic coherence studies of 1D crystalline thin …

Using Dielectric Characterization To Study Transport And Thermal Properties Of Gas/Supercritical Fluid Embedded Polymer Solution, Xiangxiao Yao

Graduate College Dissertations and Theses

Gas/supercritical fluid (SCF) and polymer mixtures are applied broadly in industry, such as rigid and light foam products for aircraft use, foamed cushion in chairs or shoes, and gas separation membranes for capturing methane from landfill gas. To understand the gas transport properties and polymer thermal properties of the mixture, we detected the dielectric properties of the mixture at two conditions and developed a novel self-designed system for high temperature and high pressure measurement.

The transport properties of physical blowing agents in polymers is viewed as a critical parameter controlling the final foam product’s foam density, cell density, and cell …

Understanding Grain Boundary And Stress Concentration Effects On Strengthening Mechanisms In Nanotwinned Metals, Qiongjiali Fang

Graduate College Dissertations and Theses

The superior strength and large tensile plasticity of nanotwinned (nt) face-centered-cubic metals have been explained by different twin size-dependent dislocation mechanisms and their inherent strengthening/softening effects. Grain boundary (GB) plasticity generally induces softening in nanocrystalline metals; however, our current understanding of the role of GBs in plasticity of nt metals remains limited. Contradicting reports exist in literature on how twin size influences stress concentration at GB – twin boundary (TB) intersections, which facilitates dislocation nucleation. In this thesis, molecular dynamics (MD) simulations and finite element analysis (FEA) were used to study the effects of GB plasticity and stress concentrations, on …