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Articles 1 - 30 of 35
Full-Text Articles in Chemistry
Controlling Mechanical Properties Of Well-Defined Polymer Networks, Ipek Sacligil
Controlling Mechanical Properties Of Well-Defined Polymer Networks, Ipek Sacligil
Doctoral Dissertations
Polymer networks are one of the most versatile and highly studied material class that revolutionized many aspects of life. Connecting the final network properties to the molecular parameters of its building blocks remains a major research thrust. Recent advances in network synthesis techniques allowed for accurate predictions of elastic modulus in model networks. Tew Group has developed highly efficient, thiol-norbornene networks with controllable mechanical properties. Chapter 2 focuses on modifying the gel fracture energy predicted by Lake-Thomas theory by accounting for loop defects. This study allowed for a priori estimates of gel fracture energy by combining theory, experiments, and simulations. …
Effect Of Chemical Identity And Morphology On Amphiphilic-Zwitterionic Block Copolymer Membranes, Ria Ghosh
Effect Of Chemical Identity And Morphology On Amphiphilic-Zwitterionic Block Copolymer Membranes, Ria Ghosh
Doctoral Dissertations
Amphiphilic block copolymers have gained a broad research interest attributed to their self-assembly properties over a range of pH, temperature, and ionic strength. Polyzwitterions have attracted special attention due to their hydrophilicity, charge sensitivity and coulombic attraction of the opposite charges over a range of environments making them a popular material of study in the field of stimuli responsive systems, for example in self-healing hydrogels, and water transport membranes. Combining the stimuli responsiveness and higher hydrophilicity of zwitterionic polymers with self-assembly behavior of amphiphilic block copolymers created an interest to study the effect of composition and identity of the zwitterionic …
Vapor Deposition Of Self-Wrinkling Polymer Films, Robert N. Enright
Vapor Deposition Of Self-Wrinkling Polymer Films, Robert N. Enright
Doctoral Dissertations
Initiated chemical vapor deposition is used to grow polymer films on substrates of various three-dimensional shapes which exhibit wrinkling during film growth, termed self-wrinkling. Self-wrinkling avoids separate film growth and compression steps and more-closely mimics processes observed in nature. The self-wrinkling process is elucidated on flat elastic substrates, revealing control over the amount of compressive stress by changing deposition conditions. Next, a study of films grown on liquid substrates with interface profiles that either resemble cylinders or contain repeating concave cones, saddles, and bowls affirms the principle that the wrinkle roundness increases with interface curvature. The selection of high versus …
Frontiers In The Self-Assembly Of Charged Macromolecules, Khatcher O. Margossian
Frontiers In The Self-Assembly Of Charged Macromolecules, Khatcher O. Margossian
Doctoral Dissertations
The self-assembly of charged macromolecules forms the basis of all life on earth. From the synthesis and replication of nucleic acids, to the association of DNA to chromatin, to the targeting of RNA to various cellular compartments, to the astonishingly consistent folding of proteins, all life depends on the physics of the organization and dynamics of charged polymers. In this dissertation, I address several of the newest challenges in the assembly of these types of materials. First, I describe the exciting new physics of the complexation between polyzwitterions and polyelectrolytes. These materials open new questions and possibilities within the context …
Enabling Nanoimprint Lithography Techniques Across Multiple Manufacturing Processes, Vincent Einck
Enabling Nanoimprint Lithography Techniques Across Multiple Manufacturing Processes, Vincent Einck
Doctoral Dissertations
Advanced nanooptics in the areas of flat lenses, diffractive elements, and tunable emissivity require a route to high throughput manufacturing. Nanooptics are often demanding of high refractive index materials, nanometer precision and ease of fabrication. Nanoimprint lithography (NIL) is a low-cost, high throughput manufacturing technique beginning to be realized in commercial industry.1,2 The NIL process is an ideal manufacturing candidate due to its ability to have a fast process time, efficient use of materials, repeatability and high precision while also having wide diversity of potential structures and material choices. Appling NIL techniques to other facets of manufacturing enable the …
Synthesis, Fabrication, And Assembly Of Mesoscale Polymer Filaments, Dylan M. Barber
Synthesis, Fabrication, And Assembly Of Mesoscale Polymer Filaments, Dylan M. Barber
Doctoral Dissertations
Mesoscale materials, with feature sizes in the range of one hundred nanometers to tens of micrometers, are ubiquitous in Nature. In organisms, mesoscale building blocks connect the properties of underlying molecular and nanoscructures to those of macroscale, organism-scale materials through hierarchical assemblies of recurring structural motifs. The collective action of large numbers of mesoscale features can afford stunning features like the structural color of the morpho butterfly wing, calcium ion-mediated movement in muscle, and wood structures like xylem that can support enormous external compressive loads and negative internal pressure to transport nutrients throughout an organism. In synthetic systems, the design, …
Designing Nonflammable Polymers And Blends Containing Deoxybenzoin Derivatives, Elizabeth Stubbs
Designing Nonflammable Polymers And Blends Containing Deoxybenzoin Derivatives, Elizabeth Stubbs
Doctoral Dissertations
The importance of synthetic polymers in everyday life continues to grow, owing to their societal importance for improving our standard-of-living and enabling advances spanning medicine, electronics, construction materials, transportation. While niche applications occupy a small fraction of the overall volume of polymers produced, large scale applications tend to employ lower cost materials, such as polyethylene, polypropylene, and polystyrene. In addition to environmental considerations connected to these polymerized hydrocarbons, produced in excess of 380 million tons per year worldwide, their inherent flammability creates additional requirements associated with their manufacturing and use. Societal benefits of such polymers are extensive, and thus, there …
Tailoring Interfaces And Composition For Stable And Efficient Perovskite Solar Cells, Hamza Javaid
Tailoring Interfaces And Composition For Stable And Efficient Perovskite Solar Cells, Hamza Javaid
Doctoral Dissertations
Metal halide perovskite solar cells (PSCs) have revolutionized the field of thin film photovoltaics. Within a decade, the power conversion efficiencies (PCEs) have increased at a phenomenal rate, rising from 3.8% to more than 25% in single-junction devices, moving them ahead of the current silicon-based technology. The high efficiencies of perovskite solar cells (PSCs) and their other unique properties arise from a combination of organic and inorganic components and electronic-ionic conduction, making them excellent candidates for a plethora of applications. However, PSCs face a significant—and ironic—roadblock to commercialization: these light-harvesting materials degrade under sunlight—the very condition they would need …
Advanced Materials Design Using Application-Based Processing Techniques, Daniel S. Camarda
Advanced Materials Design Using Application-Based Processing Techniques, Daniel S. Camarda
Doctoral Dissertations
This dissertation pertains to generating advanced materials using application-based processing techniques. First, billets consisting of PTFE sintering powders are evaluated using Thermomechancal Analysis. It was found that both shape change and volume change are associated with enthalpic and entropic recoil, respectively. These phenomena, due to melting and stored energy during the powder compaction process, were found to be molecular weight dependent. Additionally, kinetics of the recovery and sintering process were found to be slower in blended specimens than pure samples. Next, the creation of graft copolymers by selectively grafting a second polymer to the amorphous fraction of a semi-crystalline polymer …
Designing Stimuli-Responsive Nanocomposites To Investigate Interface Dynamics, Huyen Vu
Designing Stimuli-Responsive Nanocomposites To Investigate Interface Dynamics, Huyen Vu
Doctoral Dissertations
Inspired by nature, this research focuses on designing multifunctional renewable nanocomposites with high toughness and stimuli-responsiveness. In recent years, cellulose nanocrystals (CNCs) have been explored due to their abundance, renewable resource, and unique mechanical strength and structural coloration. CNCs naturally self-assemble into the helicoidal (Bouligand) structure that effectively endure high impacts but is brittle without an attendant soft phase. A thermoresponsive polymer, poly(diethylene glycol methyl ether methacrylate) (PMEO2MA), was incorporated into CNCs via evaporation-induced self-assembly to improve toughness of the resulting nanocomposites and to study responses in polymer dynamics under varying temperature and humidity conditions. To study microscopic …
Thermoelectric Transport In Disordered Organic And Inorganic Semiconductors, Meenakshi Upadhyaya
Thermoelectric Transport In Disordered Organic And Inorganic Semiconductors, Meenakshi Upadhyaya
Doctoral Dissertations
The need for alternative energy sources has led to extensive research on optimizing the conversion efficiency of thermoelectric (TE) materials. TE efficiency is governed by figure-of-merit (ZT) and it has been an enormously challenging task to increase ZT > 1 despite decades of research due to the interdependence of material properties. Most doped inorganic semiconductors have a high electrical conductivity and moderate Seebeck coefficient, but ZT is still limited by their high lattice thermal conductivity. One approach to address this problem is to decrease thermal conductivity by means of alloying and nanostructuring, another is to consider materials with an inherently low …
Theory And Improved Methods For Probing The Cavitation To Fracture Transition, Christopher Barney
Theory And Improved Methods For Probing The Cavitation To Fracture Transition, Christopher Barney
Doctoral Dissertations
A material is considered soft when its bulk modulus is significantly greater than its shear modulus. Rubbery polymers are a class of soft materials where resistance to extension is mainly entropic in nature. Polymeric soft solids differ from liquids due to the presence of a percolated network of strong bonds that resist deformation and flow on a given time scale. The incompressible nature, entropically driven elasticity, and molecular scale network structure of soft polymeric solids combine to impart unique mechanical behavior that often results in complex material responses to simple loading situations. An important example of this is cavitation in …
Top-Down And Bottom-Up Fabrication Of Key Components In Miniature Energy Storage Devices, Wenhao Li
Top-Down And Bottom-Up Fabrication Of Key Components In Miniature Energy Storage Devices, Wenhao Li
Doctoral Dissertations
The advent of miniature electronic devices demands power sources of commensurate form factors. This spurs the research of micro energy storage devices, e.g., 3D microbatteries. A 3D microbattery contains nonplanar microelectrodes with high aspect ratio and high surface area, separated by a nanoscale electrolyte. The device takes up a total volume as small as 10 mm3, allowing it to serve on a chip and to provide power in-situ. The marriage of nanotechnology and electrochemical energy storage makes microbattery research a fascinating field with both scientific excitement and application prospect. However, successful fabrication of well-functioned key components …
Designing Ion-Containing Polymers With Controlled Structure And Dynamics, Joshua Enokida
Designing Ion-Containing Polymers With Controlled Structure And Dynamics, Joshua Enokida
Doctoral Dissertations
Ion-containing polymers are a unique class of materials for which strong electrostatic interactions dictate physical properties. By altering molecular parameters, such as the backbone chemical structure, the ion content, and the ion-pair identity, the structure and dynamics of these polymers can be altered. Further investigation of the molecular parameters that govern their structure-property relationships is critical for the future development of these polymeric materials. Particularly, the incorporation of ammonium-based counterions into these polymers offers a facile method to tune their electrostatic interactions and hydrophobicity. Applying this concept, a bulky dimethyloctylammonium (DMOA) counterion was used to modify the organic solubility of …
Double-Network Materials Via Frontal Polymerization & Supercritical Co2 Processing, Matthew Joseph Lampe
Double-Network Materials Via Frontal Polymerization & Supercritical Co2 Processing, Matthew Joseph Lampe
Doctoral Dissertations
This dissertation presents work focused on producing materials in non-equilibrium states by taking advantage of novel processing techniques. First, epoxy-based resins which can undergo radically promoted, cationic, thermal, frontal polymerization are investigated for their potential use as adhesives. These resins are found to be capable of sustaining propagating polymerization fronts between several different substrate materials, resulting in high levels of adhesion in some cases. In addition, a similar frontal resin was developed that can undergo sequential gelation and frontal polymerization. The gels are formed by radically crosslinking acrylate monomers within the epoxy resin. These gels can then be manipulated, and …
Synthesis And Molecular Transport Studies In Zeolites And Nanoporous Membranes, Vivek Vattipalli
Synthesis And Molecular Transport Studies In Zeolites And Nanoporous Membranes, Vivek Vattipalli
Doctoral Dissertations
The advent of nanoporous materials such as zeolites and nanoporous membranes has provided cost-effective solutions to some of the most pressing problems of the 20th century such as the conversion of crude oil into fuels and valuable chemicals. Hierarchical zeolites and mesoporous inorganic membranes are showing great promise in addressing new problems such as the conversion of biomass into value-added chemicals and development of energy-efficient separation processes. The synthesis and fundamental aspects of molecular transport in these new materials with hierarchical porosities need to be better understood in order to rationally develop them for these desired applications. Pore narrowing …
Computational Studies Of Structure–Function Relationships Of Supported And Unsupported Metal Nanoclusters, Hongbo Shi
Computational Studies Of Structure–Function Relationships Of Supported And Unsupported Metal Nanoclusters, Hongbo Shi
Doctoral Dissertations
Fuel cells have been demonstrated to be promising power generation devices to address the current global energy and environmental challenges. One of the many barriers to commercialization is the cost of precious catalysts needed to achieve sufficient power output. Platinum-based materials play an important role as electrocatalysts in energy conversion technologies. In order to improve catalytic efficiency and facilitate rational design and development of new catalysts, structure–function relationships that underpin catalytic activity must be understood at a fundamental level. First, we present a systematic analysis of CO adsorption on Pt nanoclusters in the 0.2-1.5 nm size range with the aim …
Analyses Of Densely Crosslinked Phenolic Systems Using Low Field Nmr, Jigneshkumar Patel
Analyses Of Densely Crosslinked Phenolic Systems Using Low Field Nmr, Jigneshkumar Patel
Doctoral Dissertations
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multi-components, especially for the crosslinking of rigid high-performance materials. In these reactions, miscibility is crucial for curing efficiency. This miscibility is typically enhanced by adding a third component, a plasticizer. For the reaction of the highly crystalline crosslinking agent hexamethylenetetramine (HMTA) with a strongly hydrogen-bonded phenol formaldehyde resin, furfural has been traditionally used as the plasticizer. However, the reason for its effectiveness is not clear. In this doctoral thesis work, miscibility and crosslinking efficiency of plasticizers in phenolic curing reactions are studied by thermal analysis and spectroscopic …
Polyorganosiloxanes: Molecular Nanoparticles, Nanocomposites And Interfaces, Daniel H. Flagg
Polyorganosiloxanes: Molecular Nanoparticles, Nanocomposites And Interfaces, Daniel H. Flagg
Doctoral Dissertations
Five research projects described. First, a reproducible, lab-scale synthesis of MQ silicone copolymers is presented. MQ copolymers are commercially important materials that have been ignored by the academic community. One possible reason for this is the difficulty of controlling and reproducing the preparative copolymerizations that have been reported. A reproducible method for lab-scale preparation was developed that controls molecular weight by splitting the copolymerization into the discrete steps of sol growth from silicate precursor and end-capping by trimethylsiloxy groups. Characterization of MQ products implicates that they are composed of highly condensed, polycyclic structures. The MQ copolymers prepared in the first …
Characterization Of Electronic And Ionic Transport In Soft And Hard Functional Materials, Lawrence A. Renna
Characterization Of Electronic And Ionic Transport In Soft And Hard Functional Materials, Lawrence A. Renna
Doctoral Dissertations
Control over concurrent transport of multiple carrier types is desired in both soft and hard materials. For both types of materials, I demonstrate ways to characterize and execute governance over both electronic and ionic transport, and apply these concepts in the fabrication of devices with applications in conducting composites, photovoltaics, electrochemical energy storage, and memristors. In soft materials, such as polymers, the topology of the binary polymer mesoscale morphology has major implications on the charge/ion transport. Traditional approaches to co-continuous structures involve either using blends of polymers or diblock copolymers. In polymer blends, the structures are kinetically trapped and …
Thiol-Ene Chemistry As An Enabler Of New Polymer Structures And Architectures, Joel M. Sarapas
Thiol-Ene Chemistry As An Enabler Of New Polymer Structures And Architectures, Joel M. Sarapas
Doctoral Dissertations
This dissertation focuses on two distinct projects: the synthesis and design of novel cell penetrating peptides mimics (CPPMs), and the implementation of the thiol-ene click reaction to generate new polymer architectures and chemistries. Guanidinium-rich CPPMs were generated through both ROMP and RAFT polymerizations, allowing for a comparison to be made across polymer backbone chemistries with respect to both siRNA and protein cellular internalization. A particularly effective methacrylate derived block copolymer was able to deliver siRNA to nearly an entire Jurkat T cell population. The thiol-ene reaction was implemented initially within the context of improving material design for solid polymer electrolytes …
Evaporation Induced Self-Assembly And Characterization Of Nanoparticulate Films: A New Route To Bulk Heterojunctions, Yipeng Yang
Evaporation Induced Self-Assembly And Characterization Of Nanoparticulate Films: A New Route To Bulk Heterojunctions, Yipeng Yang
Doctoral Dissertations
Polymer-based semiconducting materials are promising candidates for large-scale, low-cost photovoltaic devices. To date, the efficiency of these devices has been low in part because of the challenge of optimizing molecular packing while also obtaining a bicontinuous structure with a characteristic length comparable to the exciton diffusion length of 10 to 20 nm. In this dissertation we developed an innovative evaporation-induced nanoparticle self-assembly technique, which could be an effective approach to fabricate uniform, densely packed, smooth thin films with cm-scale area from home-made P3HT nanoparticles. Unlike the previous reports of nanoparticle-based film formation, we use a mixture of two solvents so …
Cell Modulation Using Functionalized Nanoparticles, Rui Tang
Cell Modulation Using Functionalized Nanoparticles, Rui Tang
Doctoral Dissertations
Monolayer functionalized ultra-small gold nanoparticles (AuNPs) provide a versatile platform for applications in cell research. Through rational design of surface ligands, the chemistry of AuNPs are precisely regulated at atomic level. In this dissertation, applications of AuNPs in cell modulation are discussed. The topics are split into two categories. In the first category, functionalized AuNPs are harnessed to generate a robust monolayer on cell culture surface for cell modulation. The proliferation and behavior of different types of cancer cells and normal cells are modulated by tuning the surface ligands of AuNPs. Fate decision of mesenchymal stem cells are also modulated …
Polymer And Small Molecule Designs For Anion Conducting Membranes: Connected Ion-Channel Morphologies And Highly Alkaline Stable Ammonium Cations, Sedef P. Ertem
Doctoral Dissertations
Fuel cells are one of the oldest sustainable energy generation devices, converting chemical energy into electrical energy via reverse-electrolysis reactions. With the rapid development of polymer science, solid polymer electrolyte (SPE) membranes replaced the conventional liquid ion transport media, rendering low-temperature fuel cells more accessible for applications in portable electronics and transportation. However, SPE fuel cells are still far from commercialization due to high operation cost, and insufficient lifetime and performance limitations. Anion exchange membrane fuel cells (AEMFCs) are inexpensive alternatives to current proton exchange membrane fuel cell (PEMFC) technology, which relies on utilizing expensive noble-metal catalysts and perfluorinated SPE …
Refractive Index Engineering And Optical Properties Enhancement By Polymer Nanocomposites, Cheng Li
Refractive Index Engineering And Optical Properties Enhancement By Polymer Nanocomposites, Cheng Li
Doctoral Dissertations
The major part of this dissertation discusses the engineering of the refractive index of materials using solution-processable polymer nanocomposites and their applications in building optical components and devices. Three particular polymer nanocomposites have been introduced to achieve materials with tunable refractive indices and enhanced optical properties, which can be used to manipulate the behavior of light or electromagnetic radiations. In the first system, polyhedral oligomeric silsesquioxane (POSS)/polymer nanocomposites are developed. Thin films with tunable, low refractive indicies were fabricated from the composites. The mechanical strength of these films was characterized, and their application in antireflective coatings is discussed. In the …
(I) Polymer Nanocomposites: Rheology And Processing For Mesoporous Materials And (Ii) Nanopatterning Of Metal Oxides Using Soft Lithography, Rohit Kothari
Doctoral Dissertations
The research in this dissertation is categorized into two parts. The first part is focused on investigation of order-to-disorder transitions (ODT) in nanocomposites of an amphiphilic block copolymer containing various hydrogen-bonded additives, and fabrication of novel mesoporous silica based materials by utilizing such nanocomposites as templates. Disordered Pluronic®, poly(ethylene oxide) (PEO)−poly(propylene oxide) (PPO)−PEO triblock copolymer upon blending with small molecule additives containing hydrogen-bond-donating functional groups (carboxyl or hydroxyl) result into ordered nanoscale morphologies by preferentially interacting with the hydrophilic PEO chains in the Pluronic®. The dependence of ODT-temperature in these novel Pluronic®/small-molecule-additive complexes on composition, number and type of functional …
Morphology Evolution Mechanisms Of Low Band Gap Polymer-Based Photovoltaics, Sunzida Ferdous
Morphology Evolution Mechanisms Of Low Band Gap Polymer-Based Photovoltaics, Sunzida Ferdous
Doctoral Dissertations
An optimal nanoscale phase separation between the donor (generally, a conjugated polymer) and the acceptor (generally, a fullerene derivative) materials is one of the major requirements for obtaining high efficiency organic photovoltaic (OPV) device. Recent methods of controlling such nanostructure morphology in a bulkheterojunction (BHJ) OPV device involve addition of a small amount of solvent additive to the donor and acceptor solutions. The idea is to retain the acceptor materials into the solution for a longer period of time during the film solidification process, thus allowing the donor material to crystallize earlier. The ultimate morphology resulting from the solvent casting …
Tunable Photonic Multilayers From Stimulus-Responsive, Photo-Crosslinkable Polymers, Maria C. Chiappelli
Tunable Photonic Multilayers From Stimulus-Responsive, Photo-Crosslinkable Polymers, Maria C. Chiappelli
Doctoral Dissertations
This dissertation describes the synthesis of photo-crosslinkable copolymers and their utilization for the fabrication and testing of tunable and responsive one-dimensional (1D) photonic multilayers. Photonic multilayers exhibit structural color due to the interference of incident light at layer interfaces, providing a convenient route towards optically responsive materials that do not rely on potentially light- or oxygen-sensitive chromophore-containing pigments and dyes. A fabrication technique based on sequential spin-coating and crosslinking of photo-crosslinkable polymers is used to assemble tunable and responsive photonic multilayers. Chapter One introduces the fundamental underlying principles of 1D photonic structures and explores their importance in a variety of …
Functional Nanostructures From Nanoparticle Building Blocks, Jimmy Lawrence
Functional Nanostructures From Nanoparticle Building Blocks, Jimmy Lawrence
Doctoral Dissertations
Advances in the synthetic strategies of engineered nanomaterials, multifunctional molecules and polymers have opened pathways for the development of functional nanomaterials having unique optoelectronic, mechanical, and biological properties. By designing the chemistry of surface ligands, the organic interface of nanoparticles, one can further the versatility and utilization of engineered nanomaterials, opening pathways for breakthroughs in sensing, catalysis, and delivery using nanomaterials. This thesis describes the synthesis and characterization of small molecule and polymer ligand functionalized inorganic nanoparticles (e.g., metal, semiconducting). Embedding specific chemical functionality into the ligand periphery of nanoparticles enables the resulting functional nanoparticles to react selectively …
Functional Nanocomposites From Self-Assembly Of Block Copolymers With Nanoparticles, Xinyu Wang
Functional Nanocomposites From Self-Assembly Of Block Copolymers With Nanoparticles, Xinyu Wang
Doctoral Dissertations
This dissertation studied the proper distribution and location control of nanoparticles (NPs) within block copolymer (BCP) templates. A facile ligand exchange reaction was introduced for the hydrophilic magnetic NPs (MNPs) that are readily dispersed in polar solvents with outstanding stability. Small molecule ligands were selected to associate strongly with particle surfaces, provide hydrophilic termini for polarity matching with polar solvents, and offer the potential for hydrogen-bonding interactions to facilitate NP incorporation into polymers. Areal ligand densities of NPs indicated a significant increase in the ligand coverage after the exchange reaction. Hydrophilic MNPs were shown to drive the self-assembly of BCPs …