Matching Items (21)

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Construction and Operation of a Hollow Fiber Membrane Spinning Apparatus

Description

This study details the construction and operation of a dry-jet wet spinning apparatus for extruding hollow fiber membranes (HFMs). The main components of the apparatus are a spinneret, a coagulation

This study details the construction and operation of a dry-jet wet spinning apparatus for extruding hollow fiber membranes (HFMs). The main components of the apparatus are a spinneret, a coagulation bath, and an automatic collection reel. Continuous fiber formation was achieved using two syringe pumps simultaneously delivering polymer dope and bore fluid to the spinneret. Based on apparatus runs performed with Polysulfone (PSF) dopes dissolved in N,N-Dimethylacetamide and supporting rheological analysis, the entanglement concentration, ce, was identified as a minimum processing threshold for creating HFMs. Similarly, significant increases in the ultimate tensile strength, fracture strain, and Young's modulus for extruded HFMs were observed as polymer dope concentration was increased at levels near ce. Beyond this initial increase, subsequent tests at higher PSF concentrations yielded diminishing changes in mechanical properties, suggesting an asymptotic approach to a point where the trend would cease. Without further research, it is theorized that this point falls on a transition from the semidiute entangled to concentrated concentration regimes. SEM imaging of samples revealed the formation of grooved structures on the inner surface of samples, which was determined to be a result of the low flowrate and polymer dope concentrations used in processing the HFMs during apparatus runs. Based on continued operation of the preliminary apparatus design, many areas of improvement were noted. Namely, these consisted of controlling the collector speed, eliminating rubbing of nascent fibers against the edge of the coagulation bath by installing an elevated roller, and replacing tygon tubing for the polymer line with a luer lock adapter for direct syringe attachment to the spinneret.

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Created

Date Created
  • 2017-05

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Photocurable Networks: A Composite Materials Platform that Enables Advances in Additive Manufacturing

Description

This study aims to provide a foundation for future work on photo-responsive polymer composite materials to be utilized in additive manufacturing processes. The curing rate of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) in

This study aims to provide a foundation for future work on photo-responsive polymer composite materials to be utilized in additive manufacturing processes. The curing rate of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) in thin (<20 µm) and thick (>2 mm) layers of DMPA and poly(ethylene glycol) diacrylate (PEG-DA) mixtures was assessed for 5.0 w/v% (grams per 100 mL) concentrations of DMPA dissolved in PEG-DA. The polymerization rate and quality of curing was found to decrease as the concentration of DMPA increased beyond 1.0 w/v%; thus, confirming the existence of an optimum photo-initiator concentration for a specific sheet thickness. The optimum photo-initiator concentration for a 3-3.1 mm thick sheet of PEG-DA microstructure was determined to be between 0.3 and 0.38 w/v% DMPA. The addition of 1,6-hexanediol or 1,3-butanediol to the optimum photo-initiator concentrated solution of DMPA and PEG-DA was found to increase the Tg of the samples; however, the samples could not fully cure within 40-50 s, which suggested a decrease in polymerization rate. Lastly, the DMPA photo-initiator does not produce gaseous byproducts and is translucent when fully cured, which makes it attractive for infusion with strengthening materials because quality light penetration is paramount to quick polymerization rates. It is recommended that more trials be conducted to evaluate the mechanical properties of the optimum curing rate for DMPA and PEG-DA microstructures as well as a mechanical property comparison following the addition of either of the two alcohols.

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Created

Date Created
  • 2016-12

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A Model of Nanoparticle Dispersion in Electrospun Nanofibers

Description

Polymer-nanoparticle composites (PNCs) show improved chemical and physical properties compared to pure polymers. However, nanoparticles dispersed in a polymer matrix tend to aggregate due to strong interparticle interactions. Electrospun nanofibers

Polymer-nanoparticle composites (PNCs) show improved chemical and physical properties compared to pure polymers. However, nanoparticles dispersed in a polymer matrix tend to aggregate due to strong interparticle interactions. Electrospun nanofibers impregnated with nanoparticles have shown improved dispersion of nanoparticles. Currently, there are few models for quantifying dispersion in a PNC, and none for electrospun PNC fibers. A simulation model was developed to quantify the effects of nanoparticle volume loading and fiber to particle diameter ratios on the dispersion in a nanofiber. The dispersion was characterized using the interparticle distance along the fiber. Distributions of the interparticle distance were fit to Weibull distributions and a two-parameter empirical equation for the mean and standard deviation was found. A dispersion factor was defined to quantify the dispersion along the polymer fiber. This model serves as a standard for comparison for future experimental studies through its comparability with microscopy techniques, and as way to quantify and predict dispersion in polymer-nanoparticle electrospinning systems with a single performance metric.

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Created

Date Created
  • 2016-12

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Design and Testing of Cold-Extruded High-Density Polyethylene for Student Oboe Reeds and A Qualitative Comparison of Synthetic and Cane Oboe Reeds

Description

This is a two-part thesis, completed in conjunction with my Materials Science and Engineering Capstone Project. The first part involves the design and testing of cold-extruded high-density polyethylene for student

This is a two-part thesis, completed in conjunction with my Materials Science and Engineering Capstone Project. The first part involves the design and testing of cold-extruded high-density polyethylene for student oboe reeds. The goal of this section was to create a longer-lasting reed that produces a similar sound to a cane reed, has less variation in quality, and costs less per year than cane reeds. For low-income students in particular, the cost of purchasing cane oboe reeds ($500-$2,000 per year) is simply not feasible. This project was designed to allow oboe to be a more affordable option for all students. Money should not be a factor that limits whether or a not a child is able to explore their interests. The process used to create the synthetic reed prototype involves cold-extrusion of high-density polyethylene in order to induce orientation in the polymer to replicate the uniaxial orientation of fibrous cane. After successful cold-extrusion of a high-density polyethylene (HDPE) cylinder, the sample was made into a reed by following standard reedmaking procedures. Then, the HDPE reed and a cane reed were quantitatively tested for various qualities, including flexural modulus, hardness, and free vibration frequency. The results from the design project are promising and show a successful proof of concept. The first prototype of an oriented HDPE reed demonstrates characteristics of a cane reed. The areas that need the most improvement are the flexural modulus and the stability of the higher overtones, but these areas can be improved with further development of the cold-extrusion process. The second part of this thesis is a survey and analysis focusing on the qualitative comparison of synthetic and cane oboe reeds. The study can be used in the future to refine the design of synthetic reeds, more specifically the cold-extruded high-density polyethylene student oboe reed I designed, to best replicate a cane reed. Rather than approaching this study from a purely engineering mindset, I brought in my own experience as an oboist. Therefore, the opinions of oboists who have a wide range of experience are considered in the survey. A panel of five oboists participated in the survey. They provided their opinion on various aspects of the five reeds, including vibrancy, response, stability, resistance, tone, and overall quality. Each of these metrics are rated on a scale from one to five, from unacceptable to performance quality. According to the survey, a participant's personal, hand-made cane reed is overall the most preferred option. My prototype HDPE student reed must be improved in many areas in order to rank near the other four reeds. However, its vibrancy and resistance already rival that of a Jones student reed. As this is just the first prototype, that is a significant accomplishment. With further refinement of the cold-extrusion and reedmaking method, the other areas of the HDPE reed may be improved, and the reed may eventually compete with the existing synthetic and cane reeds on the market.

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Created

Date Created
  • 2018-05

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Easily deliverable and elastic thermosensitive physical-chemical gelling hydrogels for embolization

Description

Rupture of intracranial aneurysms causes a subarachnoid hemorrhage, which is often lethal health event. A minimally invasive method of solving this problem may involve a material, which can be administered

Rupture of intracranial aneurysms causes a subarachnoid hemorrhage, which is often lethal health event. A minimally invasive method of solving this problem may involve a material, which can be administered as a liquid and then becomes a strong solid within minutes preventing flow of blood in the aneurysm. Here we report on the development of temperature responsive copolymers, which are deliverable through a microcatheter at body temperature and then rapidly cure to form a highly elastic hydrogel. To our knowledge, this is the first physical-and chemical-crosslinked hydrogel capable of rapid crosslinking at temperatures above the gel transition temperature. The polymer system, poly(N-isopropylacrylamide-co-cysteamine-co-Jeffamine® M-1000 acrylamide) and poly(ethylene glycol) diacrylate, was evaluated in wide-neck aneurysm flow models to evaluate the stability of the hydrogels. Investigation of this polymer system indicates that the Jeffamine® M-1000 causes the gels to retain water, resulting in gels that are initially weak and viscous, but become stronger and more elastic after chemical crosslinking.

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Created

Date Created
  • 2013-05

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COMBINATORIAL SYNTHESIS OF INTRINSICALLY PHOTOLUMINESCENT POLY(AMINO ETHER)S AND THERMOSET RESINS

Description

Increased investigation into the development of macromolecular fluorophores has resulted in the synthesis and discovery of several potential candidates. These include modified and polymeric based dendritic structures, hyperbranched polymers and

Increased investigation into the development of macromolecular fluorophores has resulted in the synthesis and discovery of several potential candidates. These include modified and polymeric based dendritic structures, hyperbranched polymers and linear polymers. Strong inherent blue photoluminescence has been recently described in linear polyamine polymers in the absence of any chemical modifications. Here we describe the screening of amine/polyamine compounds for inherent photoluminescence. Several compounds that exhibited strong inherent blue photoluminescence following excitation with UV light were identified. Furthermore we demonstrated successful synthesis of poly(amino ether) polymers as well as chemically cross-linked poly(amino ether) thermosets with the lead Pentaethylenehexamine which was found to have strong inherent blue photoluminescence. The polymers and thermosets were found to retain the photoluminescent properties of the original lead compound. The polymers and thermosets were investigated for their ability to sequester heavy metals from aqueous solutions. An increased decrease in initial photoluminescence was observed as the materials were incubated with increasing metal salt concentration as a result of metal binding sequestration. The poly(amino ether) polymers were found to have higher sensitivity for metal sequestration when compared to equivalent amount of linear 25 kDa polyethylenimine. The strong inherent blue photoluminescence and the ease of synthesis of the poly(amino ether) polymers and thermosets give these materials strong potential for future applications as sensors.

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Created

Date Created
  • 2015-05

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Thermal and Vibration Characterization of Flexible Heat Sinks

Description

In nature, it is commonly observed that animals and birds perform movement-based thermoregulation activities to regulate their body temperatures. For example, flapping of elephant ears or plumage fluffing in birds.

In nature, it is commonly observed that animals and birds perform movement-based thermoregulation activities to regulate their body temperatures. For example, flapping of elephant ears or plumage fluffing in birds. Taking inspiration from nature and to explore the possibilities of such heat transfer enhancements, augmentation of heat transfer rates induced by the vibration of solid and well as novel flexible pinned heatsinks were studied in this research project. Enhancement of natural convection has always been very important in improving the performance of the cooling mechanisms. In this research, flexible heatsinks were developed and they were characterized based on natural convection cooling with moderately vibrating conditions. The vibration of heated surfaces such as motor surfaces, condenser surfaces, robotic arms and exoskeletons led to the motivation of the development of heat sinks having flexible fins with an improved heat transfer capacity. The performance of an inflexible, solid copper pin fin heat sink was considered as the baseline, current industry standard for the thermal performance. It is expected to obtain maximum convective heat transfer at the resonance frequency of the flexible pin fins. Current experimental results with fixed input frequency and varying amplitudes indicate that the vibration provides a moderate improvement in convective heat transfer, however, the flexibility of fins had negligible effects.

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Created

Date Created
  • 2019

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Decision-making for utility scale photovoltaic systems: probabilistic risk assessment models for corrosion of structural elements and a material selection approach for polymeric components

Description

The solar energy sector has been growing rapidly over the past decade. Growth in renewable electricity generation using photovoltaic (PV) systems is accompanied by an increased awareness of the fault

The solar energy sector has been growing rapidly over the past decade. Growth in renewable electricity generation using photovoltaic (PV) systems is accompanied by an increased awareness of the fault conditions developing during the operational lifetime of these systems. While the annual energy losses caused by faults in PV systems could reach up to 18.9% of their total capacity, emerging technologies and models are driving for greater efficiency to assure the reliability of a product under its actual application. The objectives of this dissertation consist of (1) reviewing the state of the art and practice of prognostics and health management for the Direct Current (DC) side of photovoltaic systems; (2) assessing the corrosion of the driven posts supporting PV structures in utility scale plants; and (3) assessing the probabilistic risk associated with the failure of polymeric materials that are used in tracker and fixed tilt systems.

As photovoltaic systems age under relatively harsh and changing environmental conditions, several potential fault conditions can develop during the operational lifetime including corrosion of supporting structures and failures of polymeric materials. The ability to accurately predict the remaining useful life of photovoltaic systems is critical for plants ‘continuous operation. This research contributes to the body of knowledge of PV systems reliability by: (1) developing a meta-model of the expected service life of mounting structures; (2) creating decision frameworks and tools to support practitioners in mitigating risks; (3) and supporting material selection for fielded and future photovoltaic systems. The newly developed frameworks were validated by a global solar company.

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Created

Date Created
  • 2017

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Analysis of cavitation-induced pressure loads on compliant polymer coatings

Description

Cavitation erosion is a significant cause of wear in marine components, such as impellers, propellers or rudders. While the erosion process has been widely studied on metals, the effect of

Cavitation erosion is a significant cause of wear in marine components, such as impellers, propellers or rudders. While the erosion process has been widely studied on metals, the effect of cavitation on polymers is not well-understood. The stress response in metals differs greatly from that of polymers, e.g. rate and temperature effects are far more important, thus damage and wear mechanisms of polymers under cavitating flows are significantly different. In this work, heat-driven failure caused by viscous dissipation and void nucleation resulting from tensile stresses arising from stress wave reflections are investigated as two possible material failure mechanisms.

As a first step in developing a fundamental understanding of the cavitation erosion process on polymer surfaces, simulations are performed of the collapse of individual bubbles against a compliant surface e.g. metallic substrates with polyurea coatings. The surface response of collapse-driven impact loads is represented by a idealized, time-dependent, Gaussian pressure distribution on the surface. A two-dimensional distribution of load radii and durations is considered corresponding to characteristic of cavitating flows accelerated erosion experiments. Finite element simulations are performed to fit a response curve that relates the loading parameters to the energy dissipated in the coating and integrated with collapse statistics to generate an expected heat input into the coating.

The impulsive pressure, which is generated due to bubble collapse, impacts the material and generates intense shock waves. The stress waves within the material reflects by interaction with the substrate. A transient region of high tensile stress is produced by the interaction of these waves. Simulations suggests that maximum hydrostatic tension which cause failure of polyurea layer is observed in thick coating. Also, the dissipated viscous energy and corresponding temperature rise in a polyurea is calculated, and it is concluded that temperature has influence on deformation.

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Agent

Created

Date Created
  • 2015

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Poly(amino ether) based Polymeric and Nanoparticle Systems for Nucleic Acid Delivery and Bioimaging

Description

Gold nanoparticles have emerged as promising nanomaterials for biosensing, imaging, photothermal treatment and therapeutic delivery for several diseases, including cancer. We have generated poly(amino ether)-functionalized gold nanorods (PAE-GNRs) using a

Gold nanoparticles have emerged as promising nanomaterials for biosensing, imaging, photothermal treatment and therapeutic delivery for several diseases, including cancer. We have generated poly(amino ether)-functionalized gold nanorods (PAE-GNRs) using a layer-by-layer deposition approach. Sub-toxic concentrations of PAE-GNRs were employed to deliver plasmid DNA to prostate cancer cells in vitro. PAE-GNRs generated using 1,4C-1,4Bis, a cationic polymer from our laboratory demonstrated significantly higher transgene expression and exhibited lower cytotoxicities when compared to similar assemblies generated using 25 kDa poly(ethylene imine) (PEI25k-GNRs), a current standard for polymer-mediated gene delivery. Additionally, sub-toxic concentrations of 1,4C-1,4Bis-GNR nanoassemblies were employed to deliver expression vectors that express shRNA ('shRNA plasmid') against firefly luciferase gene in order to knock down expression of the protein constitutively expressed in prostate cancer cells. The roles of poly(amino ether) chemistry and zeta-potential in determining transgene expression efficacies of PAE-GNR assemblies were investigated. The theranostic potential of 1,4C-1,4Bis-GNR nanoassemblies was demonstrated using live cell two-photon induced luminescence bioimaging. The PAE class of polymers was also investigated for the one pot synthesis of both gold and silver nanoparticles using a small library poly(amino ethers) derived from linear-like polyamines. Efficient nanoparticle synthesis dependent on concentration of polymers as well as polymer chemical composition is demonstrated. Additionally, the application of poly(amino ether)-gold nanoparticles for transgene delivery is demonstrated in 22Rv1 and MB49 cancer cell lines. Base polymer, 1,4C-1,4Bis and 1,4C-1,4Bis templated and modified gold nanoparticles were compared for transgene delivery efficacies. Differences in morphology and physiochemical properties were investigated as they relate to differences in transgene delivery efficacy. There were found to be minimal differences suggestion that 1,4C-1,4Bis efficacy is not lost following use for nanoparticle modification. These results indicate that poly(amino ether)-gold nanoassemblies are a promising theranostic platform for delivery of therapeutic payloads capable of simultaneous gene silencing and bioimaging.

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Agent

Created

Date Created
  • 2014