Engineering Commons^™

Using Afm-Ir To Study Nanoscopic Phase Behavior Of Polymer Blends And Photovoltaic Bulk Heterojunctions, Nathaniel L. Prine

Dissertations

Conjugated polymers (CPs) and polymer blends harbor the potential for high-performance organic solar cells (OSCs) due to their short energy payback time, low cost, solution processability, lightweight attributes, and flexibility. However, OSCs suffer from poor thermal stability compared to their inorganic equivalents. This study explores the thermal instability of OSCs, focusing on phase separation of the photoactive layer under heat, resulting in morphology changes and degradation of power conversion efficiency (PCE). Utilizing atomic-force microscopy coupled with infrared spectroscopy (AFM-IR) and differential scanning calorimetry (DSC), we delve into thermal stability-morphology relationships to devise strategies to improve OSC blend durability under thermal …

Receptor-Doped Organic Transistors: Transducing Anion Binding From Mixed Ionic-Electronic Transport, Anthony Benasco

Dissertations

Organic semiconductors based on π-conjugated polymers show remarkable properties such as high tolerance to structural defects, low processing temperature requirements, biocompatibility, ease of fabrication, and tunable properties. Conjugated polymers integrated into device arrays can exhibit collective properties sensitive to minor perturbations in the surrounding media. However, these devices rely on serendipitous sensitivity to the analyte of interest, and strategies for specific detection remain a considerable change. There remains a compelling, global need for technologies to monitor phosphate due to its prevalence in agricultural runoff, leading to fish kills and economic decline for commercial and recreational fisheries. The strong hydration energies …

Epoxy Curing: Paramount Or Trivial? A Cure Path Dependent Inquiry, Jared Bates

Dissertations

The presented research delves into epoxy network formation corroborating reactant concentration profiles and physical property development throughout cure, providing an experimental basis for burgeoning molecular dynamics and coarse-grained simulation methodologies. Herein, three primary subjects were investigated: the first two examine neat and toughened epoxide/amine network formation with respect to various cure profiles aimed at altering reaction pathways, the final chapter intends to augment traditionally utilized activation energy (E_a) methodologies.

Neat and toughened epoxide/amine slurries were monitored in-situ throughout cure via near infrared (NIR) spectroscopy and rheological techniques. Functional group conversion and moduli development were related with specific attention …

Bulk Properties Correlated To The Hydrogen Bond Organization In Dendrimers, Hyperbranched Polymers, And Linear Polymers, Beibei Chen

Dissertations

Although a lot of research was conducted on dendritic polymers, our understanding of their structure-property is still limited. Our previous study, which focused on a family of dendritic polymers based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) as a monomer, discovered unique hydrogen bond organizations contributed by their dendritic structures. However, the influence of the H-bond organization on bulk properties has yet to be understood. The goal of this dissertation is to elucidate the correlation between the H-bond organization with the dielectric and volumetric properties of bis-MPA based dendritic polymers, with an emphasis on developing a fundamental understanding of to what extent …

The Effect Of Precursor Design And Processing On The Semi-Crystalline Morphologies Of Polyacrylonitrile-Based Carbon Fiber, Katelyn Cordell

Dissertations

Basic research to control the morphology of polyacrylonitrile (PAN)-based carbon fiber is crucial for next generation composites as it determines their mechanical properties and final use. Poor molecular design of PAN-based precursors and fiber processing causes morphological defects and mechanical limitations.^1,2 This research focused on utilizing the controlled polymerization technique, reversible addition-fragmentation chain transfer (RAFT), of novel acrylamide comonomers to afford well-defined precursors with precisely controlled molecular design. This controlled RAFT technique improved the overall precursor graphitic structure as evident by the increased extent of stabilization and reduced activation energy as compared to precursors prepared by traditional free radical …

“Polysoaps” Via Raft Copolymerization To Form Well-Defined Micelles For Water Remediation And Targeted Drug Delivery Applications, Phillip Pickett

Dissertations

Amphiphilic copolymers have become increasingly important for environmental and biological applications due to their behavioral characteristics in aqueous solution. For example, structurally-tailored statistical amphiphilic copolymers or “polysoaps” can self-assemble into micelles or other architectures in water at various concentrations. Polysoaps may be differentiated from small molecule surfactant micelles in their capability to self-assemble into unimolecular associates (unimolecular micelles) with no dependence on concentration. Such micelles offer enormous potential for dispersion of hydrophobic species in water at high dilution. Importantly, each polymer chain forms its own micelle and upon dilution, these micelles remain intact and capable of dispersing hydrocarbon material in …

Chemical And Physical Modification Of Thiol-Ene And Epoxy-Amine Networks For Advanced Control Of Gas Transport And Flame Retardant Behavior, Vivek Vasagar

Dissertations

Crosslinked polymers are widely used due to its several advantages not limited to high mechanical strength combined with the easy processability. Despite of its popular usage, the fundamental understanding of polymer structure affecting the desired properties is still lacking. This PhD thesis is in two parts, the first part is devoted to the design and developing a basic understanding of structure and chemical composition dependencies of gas transport, whereas in the second part a fundamental relationship between structure to the fire-retardant properties is established.

Membrane based gas separation technique has attracted interest of selective removal of carbon dioxide gas from …

Bioinspired Glycopolymers: Models To Investigate The Effect Of Saccharide Structure And Concentration On Amyloid Beta Aggregation, Pradipta Kumar Das

Dissertations

Aggregation and subsequent deposition of amyloid-β (Aβ) peptide on neuronal cell membranes have been implicated as a cause of Alzheimer’s disease. Gangliosides in their clustered form seed and promote the Aβ aggregation process. However, the effects of the structure and the concentration of ganglioside saccharides on Aβ aggregation are not well understood. We investigated how the specific structure of saccharides (β-D-galactose and β-D-glucose) affect the aggregation pathways, kinetics, and the aggregated structures of Aβ via in vitro experiments. The effects of the local concentration of saccharides on the Aβ aggregation were also investigated.

To mimic the multivalent effect of the …

Polymer Nanocomposites Containing High Aspect Ratio Particulates: Innovation In Co-Extruded Multilayer Barrier Films, Kevin Meyers

Dissertations

Delaminated montmorillonite (MMT) clay/ maleic anhydride grafted LLDPE nanocomposite multilayer films with alternating layers of LDPE were produced through multilayer co-extrusion. The MMT concentration within the nanocomposite layers was increased through annealing the films in the melt due to a mismatch in interdiffusion rates of the polymer layers. Analysis of the nanocomposite layers upon annealing revealed that the platelets impinged upon one another resulting in significant improvement in oxygen barrier in the multilayer system, exceeding the results of bulk nanocomposites.

Model analysis demonstrated that increasing the nanoplatelet aspect ratio or initial concentration in the filled layers would lead to even …

Cellulose Reinforced Thermoplastic Composites By In-Situ Ring-Opening Polymerization, Shahab Kashani Rahimi

Dissertations

Over the past two decades, the increasing concern about the negative environmental impacts of synthetic materials has led to rising interests in utilizing renewable natural resources to develop polymer materials with comparable properties and performance to their synthetic counterparts. One of the major fields of interest is polymer composites where the replacement of synthetic fibers with bio renewable natural fibers is of great potential. However, the processing difficulties, in terms of fiber dispersion and thermal stability have limited the application of cellulosic fibers to polymers with low processing temperatures which are mostly hydrophobic polymers. As a result, the true reinforcing …

Polyisobutylene Telechelic Prepolymers By In Situ End-Quenching And Post-Polymerization Modifications, Bin Yang

Dissertations

This volume focuses on the development of telechelic polyisobutylene (PIB) prepolymers by combining end-capping of living carbocationic polymerization of isobutylene (IB) with suitable reactants and post-polymerization modifications. Alkylation kinetics of PIB tert-chloride with alkoxybenzenes using either TiCl₄ or AlCl₃ were investigated. Quantitative para-position end-capped products were only achieved if the alkoxybenzene/AlCl₃ molar ratio was greater than unity; while no such molar ratio is required for TiCl₄, but the alkylation rate was slower than AlCl₃ under the same conditions. Photopolymerization kinetics analysis of PIB triphenol tri(meth)acrylates with low and high M_ns, …

Design And Synthesis Of Dynamic Covalent Polymer Scaffolds With Controlled Architectures, Emily Annette Hoff

Dissertations

The design and synthesis of functional, controlled polymer architectures is essential to the development of new materials with precise and tailorable properties or applications. The work described in this dissertation focuses on the development of controlled polymer architectures with dynamic linkages for the design of multifunctional materials and surfaces via robust, efficient, and stimuli-responsive strategies.

In Chapter III, a post-polymerization modification strategy based on ambient temperature nucleophilic chemical deblocking of polymer scaffolds bearing N-heterocycle blocked isocyanate moieties is reported. Room temperature RAFT polymerization of three azole-N-carboxamide methacrylates, including 3,5-dimethyl pyrazole, imidazole, and 1,2,4-triazole derivatives, afforded reactive polymer scaffolds …

Nanostructured Morphologies In Glassy Polymer Networks, Brian Greenhoe

Dissertations

The body of this work describes a novel approach for the dispersion of multi-walled carbon nanotubes in a high T_g epoxy prepolymer matrix using a twin screw high-shear continuous reactor. The method demonstrated improves on previous dispersion methods in several ways. It offers increased efficiency through excellent heat transfer, while being solvent-less, scale-able, and tailorable to drive dispersion states to judiciously chosen dispersion states. Furthermore, it was shown that dispersion state and agglomerate morphology can be directed, in several ways, through processing conditions and also by controlling the matrix viscosity profile through cure. Broadband dielectric spectroscopy, optical hot-stage microscopy, …

Hybrid Aryl-Ether-Ketone And Hyperbranched Epoxy Networks, John Misasi

Dissertations

In this dissertation, relationships between chemical structures, cure kinetics and network architectures are correlated to bulk mechanical properties for novel, hybrid epoxy-amine networks. The work is split into two primary sections: the first is the synthesis and characterization of multifunctional glassy networks based on aryl-ether-ketone diamine curatives, while the second is based on the synthesis and characterization of hyperbranched epoxy polymers and their resulting networks.

Three aryl-ether-ketone (AEK) diamines of increasing molecular weights were synthesized and used to cure 4,4’-tetraglycidylether of diaminodiphenylmethane (TGDDM); the resulting networks were compared to 4,4’-diaminodiphenyl sulfone cured TGDDM. Architectural differences were created by varying cure …

Fundamental Investigations Of Clay/Polymer Nanocomposites And Applications In Co-Extruded Microlayered Systems, Jeremy John Decker

Dissertations

The second and fourth generations of hydroxylated dendritic polyesters (HBP2, HBP4) were combined with unmodified sodium montmorillonite clay (Na+MMT) in water to generate a broad range of polymer clay nanocomposites from 0 to 100% wt/wt Na+MMT. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate intercalation states of the clay galleries. It was shown that interlayer spacings were independent of generation number and changed over the composition range from 0.5 nm to 3.5 nm in 0.5 nm increments that corresponded to a flattened HBP conformation within the clay tactoids.

The HBP4/Na+MMT systems were investigated to study the …

Fluorine Containing Uv-Curable Materials For Advanced Transport Applications, James Thomas Goetz

Dissertations

The characterization of structure, thermal, gas transport, and free volume properties of two unique UV cured polymeric systems are studied and reported. In the initial pursuit of waterproof high water vapor transport membranes, it became apparent that the UV curing of fluorinated materials yielded routes to develop unique materials that fundamentally challenge conventional models for free volume and light gas transport behavior. UV-curing provides a means to rapidly “lock-in” morphologies that are accessible in the small molecule, monomer phase but rapidly become kinetically inaccessible when constraints such as covalent bonding and cross linking limit motion in the polymer system. This …

Improved Efficiency Organic Photovoltaic Cells Through Morphology Control And Process Modification, Qi Wu

Dissertations

Organic photovoltaic (OPV) cells have drawn great attention due to the potential to produce flexible, light weight, affordable solar cells using polymer organic photovoltaic materials; however, the current power conversion efficiency achieved for these systems is too low for widespread implementation of the technology. Morphology and phase separation are key factors determining the performance of organic photovoltaic cells. Precise control of the size and distribution of the phase-separated photoactive domains is necessary for optimum photon-electron conversion. Polyhedral oligomeric silsesquioxane (POSS) nanostructered chemicals have the potential to provide enhanced control of morphology, crystallinity, and phase dispersion in polymeric blend systems. In …