Engineering Commons^™

Design And Develop Lignin Based Recyclable Copolymers For Hydrophobic Coatings, Di Xie

Doctoral Dissertations

Due to the abundance, renewability, biodegradability, overall hydrophobicity, good compatibility with cellulose, and anti-UV/oxidant abilities, lignin has great application potentials in hydrophobic coatings on cellulose-based substrates. However, lignin's structural heterogeneity and rigidity challenge its value-added utilization. Herein, Kraft lignin (KL), from paper mills, is fractionated into more homogeneous fractions (FL), nanosized into lignin micro-nanospheres (LMNS), chemically modified and copolymerized with other constituents to fabricate hydrophobic coating materials with improved coating performances.

To investigate structure-property relationships of lignin-based copolymers, solvent fractionation is conducted to obtain FLs with different molecular weight (MW) and hydroxyl (OH) contents to prepare copolymers by integrating with …

Analysis Of Physicochemical Properties And Terrestrial Dynamics Of Mechanically Formed Micro-Nano Scaled Particles From Agricultural Plastic Mulches, Anton Friedrich Astner

Doctoral Dissertations

Release of microplastics (MPs) and nanoplastics (NPs) into agricultural fields is of great concern due to their reported ecotoxicity to organisms that provide beneficial service to the soil such as earthworms, and the potential ability of MPs and NPs to enter the food chain. Most fundamental studies of the fate and transport of plastic particulates in terrestrial environments employ idealized MP materials as models, such as monodisperse polystyrene spheres. In contrast, plastics that reside in agricultural soils consist of polydisperse fragments resulting from degraded films employed in agriculture. There exists a need for more representative materials in fundamental studies of …

Confinement And Interface Effects In Self Assembly Of Functional Block Copolymers, Jonathan P. Coote

Doctoral Dissertations

Functional block copolymers are of increasing interest for their ability to combine the functional properties of one polymer, such as a polymer electrolyte or semiconductor, with the mechanical properties of another polymer. Balancing properties in this way can be challenging, however, due to the complex relationship between self-assembled morphology and resulting properties. Interface effects in particular, whether due to confinement within a self-assembled domain or at macroscopic boundary, are poorly understood in such functional block copolymers. This dissertation consists of two main thrusts, each investigating confinement or interfacial effects in a different functional block copolymer system. The first thrust focuses …

Functional Bottlebrush Polymer Additives For Thin Films And Coatings, Travis S. Laws

Doctoral Dissertations

Bottlebrush polymers are a class of highly branched polymers consisting of polymeric side chains that are densely grafted to a linear backbone. Their highly branched architecture results in surface enrichment across a broad range of materials. The goal of my research has been centered around the design of functional bottlebrush polymers and their use as surface active additives in blend films and coatings.

In the first chapter, we examine the segregation behavior of polystyrene bottlebrushes that are blended with linear polystyrene. We systematically vary the lengths of the bottlebrush backbone (Nb), side-chain (Nsc), and the linear matrix (Nm) in order …

Crowd Control: Regulating The Spatial Organization Of Biopolymers And Gene Expression By Macromolecular Crowding, Gaurav Chauhan

Doctoral Dissertations

The intracellular environment is crowded with macromolecules that can occupy a significant fraction of the cellular volume. This can give rise to attractive depletion interactions that impact the conformations and interactions of biopolymers, as well as their interactions with confining surfaces. We used computer simulations to study the effects of crowding on biologically-inspired models of polymers. We showed that crowding can lead to attractive interactions between two flexible ring polymers, and we further characterized the adsorption of both flexible and semiflexible polymers onto confining surfaces. These results indicate that crowding-induced depletion interactions could play a role in the spatial organization …

Biomass Conversion To Bio-Derived Materials And Their Applications, Luna Liang

Doctoral Dissertations

Nowadays, fossil fuels still serve as the primary global energy resource. Replacing fossil fuels with renewable sources of energy and developing efficient energy storage technology is an urgent problem to solve. Lignocellulosic biomass has been investigated as a promising alternative for the production of biofuels, chemicals, and materials. In this dissertation, we studied the thermochemical biomass conversion strategies via different pretreatments strategies (e.g. dilute acid, ethanol, tetrahydrofuran, gamma-valerolactone) and genetic modification to overcome the biomass recalcitrance and achieve efficient conversion process. The biomass component structure of lignin and cellulose after thermal treatments were characterized and analyzed.

To further explore the …

Oligodimethylsiloxanes With Charged Chain Ends: Synthesis, Characterization, And Properties, Tianyu Li

Doctoral Dissertations

Charged polymers have been intensively studied because of their scientific and industrial importance. In certain cases, a single charged group in the chain end can alter the structure and properties of a polymer dramatically. On the other hand, oligomers, which are different from both discrete small molecules and higher molecular weight polymers, have become an emergent class of materials. There are several charged chain-end functionalized oligomers reported, but this area has been largely unexplored. The work described in this dissertation is aimed at using well-characterized end-group functionalized oligodimethylsiloxane (oDMS) as model materials to understand the effects of charged end groups …

Accelerated Catalyst Diffusion In Chemically Amplified Resists, Christopher M. Bottoms

Doctoral Dissertations

Quantitative reaction-diffusion models are critical for the development of high-resolution lithographic processes based on chemically amplified resists (CARs). CARs consist of a glassy polymer resin with a photoacid generator. Patterns are formed through a coupled reaction-diffusion process. It is known that reaction kinetics is controlled by the slow diffusion of acid-anion pairs (catalysts), and catalyst diffusion lengths partly control the pattern resolution and uniformity. However, it is difficult to quantify the diffusivity during reaction, let alone examine the roles of polymer-ion and ion-ion interactions on catalyst mobility, using direct measurements. This work presents a concerted experimental and computational effort to …

Structural Stability Of Thermosets During Material Extrusion Additive Manufacturing, Stian K. Romberg

Doctoral Dissertations

Over the past decade, the scale of polymer additive manufacturing has been revolutionized with machines that print massive thermoplastic parts with greater geometric complexity than can be achieved by traditional manufacturing methods. However, the heat required to print thermoplastics consumes energy and induces thermal gradients that can reduce manufacturing flexibility and final mechanical properties. With the ability to be extruded at room temperature and excellent compatibility with fibers and fillers, thermoset resins show promise to decrease the energy consumption, expand the manufacturing flexibility, and broaden the material palette offered by large-scale polymer additive manufacturing. However, structural instability in the uncured …

Characterization Techniques And Cation Exchange Membrane For Non-Aqueous Redox Flow Battery, Kun Lou

Doctoral Dissertations

The motivation of this work comes from one of the major problems of emerging non-aqueous flow battery (NAFB) that a separator or membrane which facilitates conductivity and blocks redox species crossover does not exist. Although many aspects of principles can be mirrored from mature fuel cell and aqueous flow battery, it is found that some well-defined membrane properties in aqueous systems such as swelling, transport and interactions are different in non-aqueous solvents to some extent. However, the approach of this work does follow the way perfluorosulfonate ion exchange membrane (PFSA) facilitated development of fuel cell and aqueous flow battery in …

Stretching The Applications Of Biomass: Development Of Lignin Based Thermoplastic Elastomers And Composite Materials, Anthony Stephen Bova

Doctoral Dissertations

Bio-based plastics and composites have seen increased industry adoption in recent years due to growing demand for materials with a low carbon footprint. The use of lignin as a feedstock for polymers has seen growing interest as the concept of an integrated cellulosic biorefinery gains traction and advances the need to use all components of separated biomass for value-added applications. Historically, use of lignin in thermoplastic and elastomeric copolymers and blends has been bottlenecked by the inability to introduce lignin content above 30 weight percent due to difficulties with interfacial adhesion of lignin with other soft segments. Efforts to overcome …

Unraveling The Effects Of Molecular Confinement On The Dynamics Of Polymeric Systems: I. Block Copolymer Architecture Ii. Silica Nanopores, Thomas P. Kinsey

Doctoral Dissertations

In this dissertation, broadband dielectric spectroscopy (BDS) is employed as an experimental tool to probe dipolar relaxations in polymeric systems under two types of molecular confinement. First a series of miktoarm star copolymers are used to explore how branching block copolymer architectures constrain polymer relaxations within self-assembled domains in relation to linear systems. Secondly, the effects of hard spatial confinement on the dynamics of polymer chains and of ions in polymerized ionic liquids (PILs) are studied after infiltration into silica nanochannels. Complementary techniques such as transmission electron microscopy, small angle x-ray scattering, and Raman spectroscopy are used to determine various …

All Acrylic Based Thermoplastic Elastomers: Design And Synthesis For Improved Mechanical Performance, Wei Lu

Doctoral Dissertations

Thermoplastic elastomers (TPEs) have been widely studied because of their recyclability, good processability, low production cost and distinct performance. Compared to the widely-used styrenic TPEs, acrylate based TPEs have potential advantages including exceptional chemical, heat, oxygen and UV resistance, optical transparence, and oil resistance. However, their high entanglement molecular weight lead to “disappointing” mechanical performance as compared to styrenic TPEs. The work described in this dissertation is aimed at employing various approaches to develop the all acrylic based thermoplastic elastomers with improved mechanical performance.

The first part of this work focuses on the introduction of acrylic polymers with high glass …

Innovative Electrode Nanocomposites For Energy Storage And Conversion Systems, Yiran Wang

Doctoral Dissertations

Nanocomposites emerged as suitable alternatives for electrode materials, are defined as “two or more materials with different properties remain separate and distinct on a macroscopic level within one unity and with any dimension in any phase less than 100 nm”. Recently, polymer/carbon based nanocomposites have attracted significant research interests for energy applications due to their multi-functionalities, improved structure stability and ease of production. This dissertation work focusing on the development of innovative electrode nanocomposites for proton exchange membrane fuel cell, supercapacitor and electrochromic applications.

Chapter 1 is an introduction. Chapter 2 & 3 focus on the synthesis of Pd-based nanocatalysts …

Mass And Charge Transport In Hydrated Polymeric Membranes, Marshall T. Mcdonnell

Doctoral Dissertations

Mass and charge transport through hydrated polymer membranes has significant importance for many areas of engineering and industry. Multi-scale modeling and simulation techniques were used to study transport in relation to two specific membrane applications: (1) food packaging and (2) additives for polymer electrolytes.

Chitosan/chitin films were studied due to their use as a sustainable, biodegradable food packaging film. The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in these films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane was observed to have a more homogeneous water distribution …

Solution And Surface Properties Of Architecturally- And Compositionally-Complex Block Copolymers And Their Binary Mixtures, Jesse Lawrence Davis

Doctoral Dissertations

The spontaneous generation of complex structures from polymeric building blocks provides a simple yet effective route to create useful soft matter structures having potential application in a variety of nanotechnologies. The topology, chemical structure, block composition, and sequence of the constituent building blocks of polymers are tunable through synthetic chemistry. This tunability offers attractive opportunities to generate complex, yet well-defined structures with control over the geometry, packing symmetry, and microdomain structure. This thesis work involves the study of the self-assembly behaviors of architecturally complex amphiphilic block copolymers (ABCs). ABCs are composed of two or more chemically distinct blocks that are …

Biodegradable Nano-Hybrid Polymer Composite Networks For Regulating Cellular Behavior, Charles Henley Sprague

Masters Theses

Photo-crosslinkable polymeric biomaterials have emerged in the field of biomedical research to promote tissue regeneration. For example, scaffolds that can be crosslinked and hardened in situ have been known to make suitable implant alternatives. Since injectable and photo-crosslinkable biomaterials offer the advantage of being minimally invasive, they have emerged to compete with autografts, a current highly invasive method to repair diseased tissue. A series of novel photo-crosslinkable, injectable, and biodegradable nano-hybrid polymers consisting of poly(ε-caprolactone fumarate) (PCLF) and polyhedral oligomeric silsesquioxane (POSS) has been synthesized in our laboratory via polycondensation. To engineer the material properties of the nano-hybrid networks, varied …

A Study Of Diblock Copolymer/Charged Particle Nanoporous Membranes; Morphology, Design And Transport Property Modeling, Bo Zhang

Doctoral Dissertations

A combination of self-consistent field theory and density functional theory was used to examine the stable, 3-dimensional equilibrium morphologies formed by diblock copolymers with a neutral or charged nanoparticle attached either between the two blocks or at the end of copolymer. Particle size was varied between one and four tenths of the radius of gyration of the copolymer. Phase diagrams were constructed and analyzed in terms of thermodynamic diagrams to understand the molecular-level self-assembly processes with the aim of determining the appropriate morphologies used as nanoporous membranes, (i.e. the periodic, hexagonal arrays of cylinders wherein the particles would primarily be …

Analytical And Computational Modeling Of Membrane Nanotubes, Sina Mirzaeifard

Masters Theses

This thesis investigates the interplay between cell membranes and the actin cytoskeleton in cellular structures known as membrane nanotubes. Membrane nanotubes are slender membrane structures that physically connect cells over long distances, and experiments suggest that they play a role in transferring material and information between cells. Disrupting the actin cytoskeleton disrupts membrane nanotubes. Although recent studies have revealed insight into the physical properties and functions of membrane-actin systems, further research is needed to understand their behavior in biological contexts. Membrane nanotubes provide a novel system with which to investigate interactions between the cell membrane and actin.

In this thesis, …

Composition Dependence Of The Flory-Huggins Interaction Parameter In Polymer Blends: Structural And Thermodynamic Calculations, Travis H. Russell

Doctoral Dissertations

Flory-Huggins Theory has been the basis for understanding polymer solvent and blended polymer thermodynamics for much of the last 60 years. Within this theory, a parameter (χ) [chi] was included to quantify the enthalpic energy of dispersion between distinct components. Thin film self-assembly of polymer melts and block copolymers depends critically on this parameter, and in application, χ has generally been assumed to be independent of the concentrations of the individual components of the system. However, Small-Angle Neutron Scattering data on isotopic polymer blends, such as polyethylene and deuterated polyethylene, have shown a roughly parabolic concentration dependency for …

Calculated Vs. Experimental Values For Volume And Surface Resistivity In Various Polymer Compounds, Megan Webster

Pursuit - The Journal of Undergraduate Research at The University of Tennessee

Versatile due to their resistance to high stress environments including but not limited to extreme temperature, pressure, and stress, polymers additionally have many uses in electrical applications wherein antistatic or conductive properties are preferential, i.e. conductive seals, oil pipeline spheres, and gaskets, to name a few. Being a complex material, many factors may affect the electrical resistivity of a given polymer compound including type and amount of carbon black, type of rubber, cure time and temperature, and dispersion, amongst other factors. External conditions such as relative humidity and temperature also play key roles. This paper will analyze five different rubber …

Ab Initio Studies Of Proton Transport In Proton Exchange Membranes, Jeffrey Keith Clark

Doctoral Dissertations

A molecular-level understanding of the factors that contribute to transport properties of proton exchange membranes (PEMs) for fuel cell applications is needed to aid in the development of superior membrane materials. Ab initio electronic structure calculations were undertaken on various PEM ionomer fragments to explore the effects of local hydration, side chain connectivity, protogenic group separation, and specific side chain chemistry on proton dissociation and transfer at low hydration. Cooperative interactions between both intra- and inter-molecular acidic groups and hydrogen bond connectivity were found to enhance proton dissociation at very low degrees of hydration. The energetics associated with proton transfer …

Nanolayer Polymeric Coatings To Enhance The Performance And Service Life Of Inorganic Membranes For High Temperature-High Pressure Biomass Pretreatment And Other Applications, Vincent C. Kandagor

Doctoral Dissertations

Membrane technology has become increasingly attractive in several applications including water filtration, food industry, oil and gas, and biomedical applications. Most recently the quest for renewable, bioenergy has called for use of membranes in biomass pretreatment and other stages of producing biofuel. The success and advancement of the membrane technology for these various applications has, however, been impeded by the fouling of membranes, which causes the pores in the microporous structure to block, resulting in reduced efficiency, and in some cases, total failure of the membranes system. This challenge leads to a tremendous increase in the cost of using membranes …

Membrane And Performance Study In Polymer Electrolyte Membrane Fuel Cells And Hydrogen Bromine Redox Flow Batteries, Yujia Bai

Doctoral Dissertations

This dissertation represents the consideration of the problems of polymer electrolyte membrane fuel cells (PEMFC) and hydrogen-bromine redox flow batteries (RFB). Due to the importance of water management in PEMFCs, all the experiments were strictly controlled at different water hydration conditions. Water uptake and densities were measured for Nafion^® and a series of 3M ionomer membranes. The thermodynamics of water and polymer was analyzed based on water uptake experiment and calorimetry. Furthermore, partial molar volumes (PMV) of water/membrane system was defined for the first time and used to analyze the interaction between water and polymers. Three states of water …

Structure And Energetics Of Nanoparticles And Ionomer Films In Fuel Cell Catalyst Layers, Qianping He

Doctoral Dissertations

Improving the durability and utilization efficiency of the platinum-on-carbon (Pt/C) catalyst is of vital importance to the commercialization of the polymer electrolyte membrane fuel cell (PEMFC). This body of work provides molecular level insights to aid the fulfillment of this goal. Chapter 1 describes the use of molecular dynamics (MD) simulation in an effort to understand the Pt/C degradation issue from the nano-adhesion point of view. The roles of catalyst nanoparticle size, shape, Pt/C surface oxidation and the extent of ionomer film hydration are investigated to study their effects on nano-particle adhesion. It is found that the adhesion force strengthens …

Characterization Techniques And Electrolyte Separator Performance Investigation For All Vanadium Redox Flow Battery, Zhijiang Tang

Doctoral Dissertations

The all-vanadium redox flow battery (VRFB) is an excellent prospect for large scale energy storage in an electricity grid level application. High battery performance has lately been achieved by using a novel cell configuration with advanced materials. However, more work is still required to better understand the reaction kinetics and transport behaviors in the battery to guide battery system optimization and new battery material development. The first part of my work is the characterization of the battery systems with flow-through or flow-by cell configurations. The configuration difference between two cell structures exhibit significantly different polarization behavior. The battery output can …

Structure And Morphology Of Sulfonated Polysulfone And Perfluorosulfonic Acid Ionomers, Chen Wang

Doctoral Dissertations

The limitations of conventional perfluorosulfonic acid (PFSA) based membrane materials have provoked the search for alternative materials which can function as the electrolyte in PEM fuel cells operated at higher temperatures (> 100 °C) and without humidification. A novel class of sulfonated poly(phenylene) sulfone (sPSO2) ionomers have shown much higher proton conductivity than typical PFSA membranes at elevated temperatures. In this dissertation, both computational and experimental methods were used to investigate proton transfer, morphological and structural properties of sPSO2 and PFSA ionomers. We have undertaken ab initio electronic structure calculations to understand the primary hydration and the transfer of protons …

The Impact Of Selective Solvents On The Structure And Function Evolution In Solvent Annealed Organic Photovoltaics, Sheng Hu

Masters Theses

The role of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) solubility on the evolution of structure and function in solvent annealed organic photovoltaics is quantitatively investigated. ODCB solvent vapor distribution during the solvent uptake process is simulated on a 3-D profile. Determination of solvent uptake in the P3HT/PCBM mixture shows that the evolution of the morphology during solvent annealing (SVA) takes much longer than the diffusion of the solvent vapor into the sample. The evolution of P3HT crystallinity, as well as the growth of PCBM aggregates, in the solvent annealed thin films is observed by Grazing Incidence Wide …

Modulation Of Bone And Nerve Cell Behavior Using Biodegradable Polymer Networks, Lei Cai

Doctoral Dissertations

This dissertation presents novel biodegradable and photo-crosslinkable building blocks to achieve polymer networks with controlled surface chemistry, stiffness, and topographical features for investigating cell-material interactions and targeting hard and soft tissue engineering applications. Chapter I reviews the recent progress in polymeric gel systems and how their physical properties can be tailored to regulate cell functions and satisfy the clinical needs. Chapter II presents a facile method to synthesize photo-crosslinkable poly(epsilon-caprolactone) acrylates (PCLAs) and reveal tunable cell responses to photo-crosslinked PCLAs. Chapter III investigates the mechanism of colorization in preparing crosslinkable polymers by reacting hydroxyl-containing polymers with unsaturated anhydrides or acyl …

Design Of Equipment For The Study Of Non-Isothermal Flow In Polymer Fluid, Opeoluwa Oluwaseun Kolawole

Masters Theses

The polymer industry is an ever growing industry, and, as it grows, companies are continuously looking for ways to study and understand the behaviors of polymers in relation to the processing and production. This is to ensure the production of high quality products and to improve existing products.
An important parameter during polymer processing is temperature. Temperature control affects several rheological parameters such as viscosity, and in turn the quality of the final products. Frictional or viscous heating is a very important part of polymer processing and occurs in almost every polymer processing operation.
The objective of this research is …