MS, University of Cincinnati, 2006, Engineering : Materials Science

Conductive polymer composites have long been used in sensing applications. Since the demand for such sensors is growing, further research is needed to keep pace and come up with new and improved materials. These materials have percolation structures with sufficient conductor phase dispersed in the polymer insulator matrix. The resistance in these materials can vary with temperature and gas ambience, so as to serve as sensitive sensors, with typically a sharp transition at a particular temperature. This study focused on the use of Poly Ethylene Oxide and graphite flakes. For such plate-like morphologies the conducting paths are formed at low percolation concentrations. The components were blended and hot pressed to pellets. Thermistor and gas sensing data showed sharp change. An inert ceramic additive was used to escalate the thermal stability. Microstructures and other structural features of the samples were observed using Optical microscopy and SEM to establish the structure-property correlation

Committee: Dr. Relva Buchanan (Advisor) Subjects: Engineering, Materials Science

Doctor of Philosophy, University of Akron, 2022, Polymer Engineering

Epoxy resins are versatile thermosetting resins providing properties like strength, durability, compatibility with various substrates, chemical and corrosion resistance to their cured system, making them a preferred choice in applications like aerospace, marines, electronics, and construction. Recently, the demand for lightweight multifunctional materials has increased, especially in the aerospace and electronic sectors. However, it is not easy to develop lightweight multifunctional materials using typical epoxy resin formulations consisting of epoxy resin, curing agents, fillers, and other additives. Developing multifunctional components for epoxy resin formulations is a promising approach to achieving lightweight epoxy composites. In this work, we develop a coordination polymer-based multifunctional filler for epoxy resins using an ionic liquid, 1-ethyl-3-methylimidazolium dicyanamide. The discussion involves understanding the influence of constituent ions like metal salts, ligands, and solvents on the structure and properties of coordination polymer(CP) to develop insight for engineering desired structure of CP. This work shows two approaches for synthesizing the desired CP using mineralizing agents like water and alkali chloride salts. Different starting metal salts and mineralizing alkali salts were used to understand the influence of cations and anions in the reaction system on the yield and structure of the desired CP, which helped provide insight to engineer synthesis approaches for the desired CP. The last part of the work focuses on using synthesized CP as a multifunctional filler in an epoxy system. We discuss the additive and concentration effects of CP loading in an epoxy resin system towards developing an epoxy resin-based conductive adhesive.

Committee: Ruel McKenzie (Advisor) Subjects: Aerospace Materials; Automotive Materials; Engineering; Materials Science; Polymers

Master of Science, University of Akron, 2022, Polymer Engineering

For decades, conductive polymer composites have been widely used for smart packaging and electronic applications. Carbon-based fillers like Carbon Black (CB) and Carbon Nanotubes (CNTs) gained a lot of traction and are the most commonly used conductive fillers incorporated in polymer matrices to create conductive polymer composites. Recently, research has been focused on developing composites with natural and biodegradable resources like biochar (pyrolyzed biomass) as potential conductive fillers. Biochar or other biobased resources are poor conductors of electricity, and hence they need to be used in conjunction with highly conductive fillers like CB and CNTs. Focusing on this issue, polymer composites prepared by blending Pyrolyzed soybean hulls (PSBH) in combination with CB with High-Density Polyethylene (HDPE) were investigated. Here PSBH is a less conductive, natural, and eco-friendly component, while carbon black is the highly conductive filler. In this study, the effect of PSBH on the conductive and mechanical properties of HDPE/CB composites was studied. The impact of various processing parameters like Rate of Mixing (RPM), Mixing time, and Processing Temperature on the resistivity was also investigated.

Committee: Erol Sancaktar (Advisor); Sadhan Jana (Committee Member); James Eagan (Committee Chair) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2008, Polymer Engineering

In this work, highly conductive carbon-filled epoxy composites were developed for manufacturing bipolar plates in proton exchange membrane (PEM) fuel cells. These composites were prepared by solution intercalation mixing, followed by compression molding and curing. The in-plane and through-plane electrical conductivity, thermal and mechanical properties, gas barrier properties, and hygrothermal characteristics were determined as a function of carbon-filler type and content. For this purpose, expanded graphite and carbon black were used as a synergistic combination. Mixtures of aromatic and aliphatic epoxy resin were used as the polymer matrix to capitalize on the ductility of the aliphatic epoxy and chemical stability of the aromatic epoxy. The composites showed high glass transition temperatures (Tg ~ 180°C), high thermal degradation temperatures (T2 ~ 415°C), and in-plane conductivity of 200-500 S/cm with carbon fillers as low as 50 wt%. These composites also showed strong mechanical properties, such as flexural modulus, flexural strength, and impact strength, which either met or exceeded the targets. In addition, these composites showed excellent thermal conductivity greater than 50 W/m/K, small values of linear coefficient of thermal expansion, and dramatically reduced oxygen permeation rate. The values of mechanical and thermal properties and electrical conductivity of the composites did not change upon exposure to boiling water, aqueous sulfuric acid solution and hydrogen peroxide solution, indicating that the composites provided long-term reliability and durability under PEM fuel cell operating conditions. Experimental data show that the composites developed in this study are suitable for application as bipolar plates in PEM fuel cells.

Committee: Sadhan Jana (Advisor) Subjects: Engineering, Chemical

Doctor of Philosophy, University of Akron, 2007, Polymer Science

Carbon nanofiber composites Carbon nanofiber (CNF) and carbon nanotube (CNT) composites have enhanced mechanical and electrical properties that make these composites desirable for antistatic and electronic dissipation technology. These applications require a homogeneous dispersion of CNF within a polymer matrix. To improve the compatibility/dispersibility of CNF within a polymer matrix, a hyperbranched polyol CNF composite was synthesized by the chemical modification of oxidized CNF with glycidol and boron trifluoride diethyl etherate. The resulting polyol CNF were characterized by TGA, FTIR, TEM/SEM and XPS. The hydroxyl groups were reacted with heptafluorobutyryl chloride to determine the amount of oxidized groups in the sample. The amount of hydroxyl groups increased by 417 % for the polyol CNF compared to the oxidized CNF and an improvement in dispersion ability was observed. Silver- and polyaniline-filled epoxy composites Composites with high electrical conductivity have been formulated from 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECC), undoped polyaniline (inherently conductive polymer, ICP), silver particles, and a thermal initiator capable of forming a strong Lewis acid. The incorporation of undoped polyaniline (PANI) into the silver-filled epoxy matrix provided an order of magnitude decrease in electrical resistivity (10-5 ohm-cm) compared to non-ICP matrix (10-4 ohm-cm). Formulations were characterized by SEM, TGA, solid state 13C NMR and 4-point probe conductivity. An interaction between PANI and the surfactant on the silver particles resulted in improved connectivity (aggregation and packing) of the silver particles. Furthermore, formulations using undoped PANI exhibited higher conductivity than doped PANI. Solid state 13C NMR showed that PANI became latently doped from the acid catalyst within the epoxy matrix, as well as the acidic surfactants on the surface of the silver. The ability to better disperse PANI, compared to the doped P (open full item for complete abstract)

Committee: Roderic Quirk (Advisor) Subjects: Chemistry, Polymer