<p>  </p> <p>In the time after their conception, Dielectric Barrier Discharge (DBD) systems have become highly utilized in the field of plasma research, with applications ranging from medicine to water treatments to airfoil design. One of the more recent applications for DBD systems has been the plasma treatment of polymers, overcoming the deficits of previously used chemical treatment systems such as environmental hazards, high cost, and other complexities. A novel development occurring within the past three years was the use of a DBD system to treat the inner surface of small-diameter polymer tubing to improve the wettability and adhesion characteristics as compared to untreated polymer tubing. This work is interested in improving that DBD system.</p> <p>This thesis focuses on the development and implementation of two additional systems for an atmospheric pressure DBD system that treats the inner surface of narrow-diameter polymer tubes. The first, a pulsed-DC HV generator, will improve the plasma treatment. The fast rise times of the applied voltage prevent any stochastic behavior in plasma ignition and reignition, the resulting homogeneity of the plasma means that the plasma conditions of the treatment are more easily reproduced, and the increase in plasma intensity allows for quicker treatment of the tubing, the feed rates can reach the level of industrial production without lessening the effects induced by the treatment. The second, a Capstan-driven spooling system, will also improve the industrial capabilities of the DBD system. The higher feed rates that the spooling system reaches provide a means to rapidly produce treated tubing at a continuous rate, and the user-friendly interface means that system operation increases to a broader range of potential personnel. </p> <p>Investigation of the effect that tube feed rate (plasma exposure time) has on surface wettability was performed for the feed rates of the spooling systems. Feed rates of 2.5, 10, 50, 200, and 800 mm/min were performed on tubing samples for a 100% Helium plasma at a power level of 5 mW and a 98%He-2%O2 plasma at a power level of 20 mW. The temporal evolution of wettability was determined by taking the water contact angle (θ) of the treated tubing surface 0, 1, 2, 4, 16, 24, and 120 hours after plasma treatment. The resulting water contact angles initially fluctuate but eventually decay to reach a steady-state hydrophilicity that remains up to five days. The steady-state contact angles ranged from 42.3o < θss < 70.2o for a Helium plasma and 39.9o < θss < 62.7o for a Helium-Oxygen plasma. </p> <p>Investigation of the plasma power achieved with a pulsed-DC HV generator was also performed. The pulsed DC-driven plasma, which has a characteristic rise time of ~300 ns, ignites at Vbd = 4.5 kV. This breakdown voltage is 1.3 times higher than the minimum for the system, Vbd,min = 3.45 kV, so the resulting overvoltage of the pulsed-DC generator is approximately 1.3 times the minimum breakdown voltage. The electrical power deposited to the discharge for the pulsed-DC driven discharge (133.2 mW) is 6 times the power of the previous AC-driven discharge (21.4 mW). Resulting surface wettability was also calculated for the two generators. The stronger plasma treatment of the pulsed-DC HV generator resulted in a steady-state contact angle 11.4o more hydrophilic than the AC HV generator (θss = 44.6o for pulsed-DC-driven discharge compared to θss = 56o for AC-driven discharge).</p>

The research presented in this dissertation focuses on the design and synthesis of novel hybrid conjugated polymer materials using two different approaches: 1) inorganic/organic hybrid semiconductors through the incorporation of carboranes into the polymer structure and 2) the modification of surfaces with conjugated polymers via grafting approaches. Hybrid conjugated polymeric materials, which are materials or systems in which conjugated polymers are chemically integrated with non-traditional structures or surfaces, have the potential to harness useful properties from both components of the material to help overcome hurdles in their practical realization in polymer-based devices. This work is centered around the synthetic challenges of creating new hybrid conjugated systems and their potential for advancing the field of polymer-based electronics through both greater understanding of the behavior of hybrid systems, and access to improved performance and new applications. Chapter 1 highlights the potential applications and advantages for these hybrid systems, and provides some historical perspective, along with relevant background materials, to illustrate the rationale behind this work. >Chapter 2 explores the synthesis of poly(fluorene)s with pendant carborane cages. The Ni(0) dehalogenative polymerization of a dibromofluorene with pendant carborane cages tethered to the bridging 9-position produced hybrid polymers produced polymers which combined the useful emissive characteristics of poly(fluorene) with the thermal and chemical stability of carborane cages. The materials were found to display increased glass transition temperatures and showed improved emission color stability after annealing at high temperatures relative to the non-hybrid polymer. The design and synthesis of a poly(fluorene)-based hybrid material with carborane cages in the backbone, rather than as pendant groups, begins in chapter 3. Poly(fluorene) with p-carborane in the backbone is synthesized and characterized, and the material is found to be a high MW, soluble blue emitter which shows a higher glass transition temperature and greater stability than a non-hybrid polymer. UV absorbance and fluorescence spectroscopy indicated some electronic interaction between the conjugated polymer and the cages, but they did not appear to be fully conjugated in the traditional sense. Chapter 4 describes the design, synthesis, and characterization of poly(fluorene) with o-carborane in the backbone. Profound changes in the behavior of the polymer, from its polymerization behavior to its emission characteristics, were observed and their origins are discussed. Experiments to explore the nature of the cage/polymer interactions were performed and possible applications which take advantage of the unique nature of the o-carborane hybrid polymer are explored and discussed. Hybrid conjugated polymer materials via grafting approaches to surfaces and surface modification are discussed starting in chapter 5. The synthesis of a dibromofluorene-based silane coupling agent for the surface functionalization of oxide surfaces is presented, and the surface directed Ni(0) dehalogenative polymerization of poly(dihexylfluorene) is explored. Chapter 6 focuses on the exploration of conjugated polymer/cellulose hybrid materials. Surface medication of cellulose materials with monomer-like anchor points is discussed. Grafting of the modified cellulose with conjugated polymers was explored and the grafting of three different repeat structures based on fluorene-, fluorenevinylene-, and fluoreneethynylene motifs were optimized to provide a general route to cellulose/conjugated polymer hybrid materials. Characterization and possible applications of such hybrid materials are discussed. Finally, chapter 7 is devoted to the simultaneous surface patterning and functionalization of poly(2-hydroxyethylmethacrylate) thin films using a silane infusion-based wrinkling technique. While not a conjugated polymer system, the spontaneous patterning and functionalization methods explored in this chapter produce hybrid organic/inorganic polymer thin films which have applications that range from optics, to adhesion, to polymer-based electronics, and the research compliments the other chapters. The spontaneous generation of complex patterns, of a small scale approaching 100nm feature size, over a large area with simultaneous control over surface chemistry is explored. Examples of complex, hierarchically patterned films which integrate lithographic processes such as nanoimprint lithography and electron beam lithography with spontaneous patterning via wrinkling are presented.

Respirable coal mine dust (RCMD) is one of the biggest occupational health hazards. Dusty mining environments can cause life-threatening respiratory health problems for coal miners known as black lung. Over the last 20 years, the flooded bed dust scrubber (FBS) has been employed as an integral component of dust control strategies for underground continuous mining operations. These units have been shown to be effective and robust in mining environments; however, several technical challenges and knowledge gaps limit their performance and efficiency. Despite the capability of the FBS, there are numerous technical challenges that limit its performance and efficiency. In particular, the static panel filter, instrumental in most scrubber designs, is fundamentally limited in collection efficiency and causes numerous operational challenges including rapid clogging. Furthermore, the current design of the filter panel is not capable of evenly wetting the entire surface area. This allows dust-laden air to pass through the filter media and decreases the cleaning capability of the FBS. In this research, both a lab-scale and a full-scale vibration-enhanced FBS with a liquid-coated filter panel were designed, manufactured, and tested. The results confirmed that a vibration-induced filter panel enhances dust collection performance and reduces mesh clogging. In addition, laboratory-scale mesh clogging tests showed that a hydrophilic mesh provided superior clogging mitigation and better performance. Typical results from bench-scale tests showed notable improvements in dust collection efficiencies by over 6% in wet condition and over 7% in dry condition while reducing mass accumulation in the filter by almost 10% in wet condition and over 40% in dry condition. The prototype testing was less conclusive, with deviations between the static mesh and vibrating mesh depending on the mesh density and operating conditions. Nevertheless, with the highest mesh density tested (30-layer), the vibrating mesh notably outperformed the static mesh with superior collection efficiency and reduced airflow loss. The system was further analyzed to investigate the size-by-size recovery of dust particles to various endpoints in the scrubber, under both vibrating and static conditions. Results show that while a majority of the particles are recovered into the demister sump, nearly a quarter of the dust mass is recovered upstream of the screen. In addition, the data confirm that vibration prompts notable improvements to collection efficiency, particularly in the finest size class (- 2.5 micron). / Doctor of Philosophy / Coal mine dust is an unintended and unavoidable consequence of coal extraction operations that poses significant health and safety risks. The inhalation of small, respirable dust particles can cause incurable lung diseases, including silicosis and coal workers' pneumoconiosis known as black lung. To minimize occupational hazards of underground coal mine dust, the Mine Safety and Health Administration (MSHA) periodically brings legislation to the industry. The recent respirable dust rule mandates reducing the maximum allowable respirable dust concentrations in the mine environment to below 1.5 mg/m3 at the working face and below 0.5 mg/m3 at intake entries. In order to comply with these regulations, modern mining techniques utilize several dust mitigation strategies, and the flooded-bed dust scrubber (FBS) is one such technology used extensively on continuous miners. The conventional static panel filter, instrumental in most scrubber designs, however, is fundamentally limited in collection efficiencies due to a high clogging rate and a tradeoff between mesh density and airflow rate. Moreover, poorly wetted areas allow dust-laden air to pass through the filter media. To overcome these deficiencies, a novel liquid-coated vibrating mesh panel is introduced in this research. A laboratory-scale dust scrubber unit and a full-scale unit with a vibration-enhanced mesh screen panel were manufactured and employed to investigate the efficacy of the concept as compared to that of a static mesh. A series of experimental design studies were employed to determine the effective vibrational parameters, scrubber operational parameters, and the impact of mesh variations on dust collection and clogging mitigation. Optimized results from this research were also evaluated against those of a static mesh to determine performance improvement while investigating the mechanisms controlling dust collection and particle department through the scrubber system. Results from the laboratory study show that vibrating mesh conditions, higher water flow rates, and a hydrophilic mesh screen panel led to an improvement in the cleaning efficiency of the scrubber system. Compared to a static-mesh to FBS, the vibrating-mesh FBS showed a significant reduction in pressure drop across the mesh screen indicating lower air loss through the test duration. Overall, the findings confirm that vibrating mesh conditions have the ability to improve filter clogging issues while maintaining high collection efficiencies which can lead to better and healthier working conditions and prolonged operational time with less frequent maintenance. This research supports further technological advancement in mine dust mitigation technologies.

Thermal energy storage (TES) consists in storing heat for a later use, thereby reducing the gap between energy availability and demand. The most diffused materials for TES are the organic solid-liquid phase change materials (PCMs), such as paraffin waxes, which accumulate and release a high amount of latent heat through a solid-liquid phase change, at a nearly constant temperature. To avoid leakage and loss of material, PCMs are either encapsulated in inert shells or shape-stabilized with porous materials or a nanofiller network. Generally, TES systems are only a supplementary component added to the main structure of a device, but this could unacceptably rise weight and volume of the device itself. In the applications where weight saving and thermal management are both important (e.g. automotive, portable electronics), it would be beneficial to embed the heat storage/management in the structural components. The aim of this thesis is to develop polymer composites that combine a polymer matrix, a PCM and a reinforcing agent, to reach a good balance of mechanical and TES properties. Since this research topic lacks a systematic investigation in the scientific literature, a wide range of polymer/PCM/reinforcement combinations were studied in this thesis, to highlight the effect of PCM introduction in a broad range of matrix/reinforcement combinations and to identify the best candidates and the key properties and parameters, in order to set guidelines for the design of these materials. The thesis in divided in eight Chapters. Chapter I and II provide the introduction and the theoretical background, while Chapter III details the experimental techniques applied on the prepared composites. The results and discussion are then described in Chapters IV-VII. Chapter IV presents the results of PCM-containing composites having a thermoplastic matrix. First, polyamide 12 (PA12) was melt-compounded with either a microencapsulated paraffin (MC) or a paraffin powder shape-stabilized with carbon nanotubes (ParCNT), and these mixtures were used as matrices to produce thermoplastic laminates with a glass fiber fabric via hot-pressing. MC was proven more suitable to be combined with PA12 than ParCNT, due to the higher thermal resistance. However, also the MC were considerably damaged by melt compounding and the two hot-pressing steps, which caused paraffin leakage and degradation, as demonstrated by the relative enthalpy lower than 100 %. Additionally, the PCM introduction decreased the mechanical properties of PA12 and the tensile strength of the laminates, but for the laminates containing MC the elastic modulus and the strain at break were not negatively affected by the PCM. Higher TES properties were achieved with the production of a semi-structural composite that combined PA12, MC and discontinuous carbon fibers. For example, the composite with 50 wt% of MC and 20 wt% of milled carbon fibers exhibited a total melting enthalpy of 60.4 J/g and an increase in elastic modulus of 42 % compared to the neat PA. However, the high melt viscosity and shear stresses developed during processing were still responsible for a not negligible PCM degradation, as also evidenced by dynamic rheological tests. Further increases in the mechanical and TES properties were achieved by using a reactive thermoplastic matrix, which could be processed as a thermosetting polymer and required considerably milder processing conditions that did not cause PCM degradation. MC was combined with an acrylic thermoplastic resin and the mixtures were used as matrices to produce laminates with a bidirectional carbon fabric, and for these laminates the melting enthalpy increased with the PCM weight fraction and reached 66.8 J/g. On the other hand, the increased PCM fraction caused a rise in the matrix viscosity and so a decrease in the fiber volume fraction in the final composite, thereby reducing the elastic modulus and flexural strength. Dynamic-mechanical investigation evidenced the PCM melting as a decreasing step in ’; its amplitude showed a linear trend with the melting enthalpy, and it was almost completely recovered during cooling, as evidenced by cyclic DMA tests. Chapter V presents the results of PCM-containing thermosetting composites. A further comparison between MC and ParCNT was performed in a thermosetting epoxy matrix. First, ParCNT was mixed with epoxy and the mixtures were used as matrices to produce laminates with a bidirectional carbon fiber fabric. ParCNT kept its thermal properties also in the laminates, and the melting enthalpy was 80-90 % of the expected enthalpy. Therefore, ParCNT performed better in thermosetting than in thermoplastic matrices due to the milder processing conditions, but the surrounding matrix still partially hindered the melting-crystallization process. Therefore, epoxy was combined with MC, but the not optimal adhesion between the matrix and the MC shell caused a considerable decrease in mechanical strength, as also demonstrated by the fitting with the Nicolais-Narkis and Pukanszky models, both of which evidenced scarce adhesion and considerable interphase weakness. However, the Halpin-Tsai and Lewis-Nielsen models of the elastic modulus evidenced that at low deformations the interfacial interaction is good, and this also agrees with the data of thermal conductivity, which resulted in excellent agreement with the Pal model calculated considering no gaps at the interface. These epoxy/MC mixtures were then reinforced with either continuous or discontinuous carbon fibers, and their characterization confirmed that the processing conditions of an epoxy composite are mild enough to preserve the integrity of the microcapsules and their TES capability. For continuous fiber composites, the increase in the MC fraction impaired the mechanical properties mostly because of the decrease in the final fiber volume fraction and because the MC phase tends to concentrate in the interlaminar region, thereby lowering the interlaminar shear strength. On the other hand, a small amount of MC enhanced the mode I interlaminar fracture toughness (Gic increases of up to 48 % compared to the neat epoxy/carbon laminate), as the MC introduced other energy dissipation mechanisms such as the debonding, crack deflection, crack pinning and micro-cracking, which added up to the fiber bridging. Chapter VI introduces a fully biodegradable TES composite with a thermoplastic starch matrix, reinforced with thin wood laminae and containing poly(ethylene glycol) as the PCM. The wood laminae successfully acted as a multifunctional reinforcement as they also stabilized PEG in their inner pores (up to 11 wt% of the whole laminate) and prevent its leakage. Moreover PEG was proven to increase the stiffness and strength of the laminate, thereby making the mechanical and TES properties synergistic and not parasitic. Finally, Chapter VII focused on PCM microcapsules. The synthesis of micro- and nano-capsules with an organosilica shell via a sol-gel approach clarified that the confinement in small domains and the interaction with the shell wall modified the crystallization behavior of the encapsulated PCM, as also evidenced by NMR and XRD studies and confirmed by DSC results. In the second part of Chapter VII, a coating of polydpamine (PDA) deposited onto the commercial microcapsules MC. The resulting PDA coating was proven effective to enhance the interfacial adhesion with an epoxy matrix, as evidenced by SEM micrographs. XPS demonstrated that the PDA layer was able to react with oxirane groups, thereby evidencing the possibility of forming covalent bond with the epoxy matrix during the curing step.

This research investigates the efficacy of liquid-precursor thermal spray coating (TSC) as a facile wood modification technique to bring hydrophobicity and UV durability to a wooden surface. The technique was successful in depositing Cu and TiO2 particles onto southern yellow pine (SYP) veneers by using copper azole, copper quaternary, and titanium tetraisopropoxide as the precursor solutions. Using optimized settings, the average coating surface coverage of > 90% and an average coating thickness of > 5 μm were obtained. The coatings displayed up to 4H rating in the film hardness scale and up to 3B rating in adhesion strength scale, suggesting reasonable mechanical durability under mild mechanical abrasion. TSC-modified wood with TiO2 created a water repellent layer, yielding a significant increase in hydrophobicity that changed the water contact angle from 57° to 126°. Accelerated weathering test results showed that the TSC-modified wood was more resistant to discoloration compared to unmodified wood.

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