Browsing by Subject "Coating"
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Item Amphiphilic Hyperbranched Fluoropolymer Networks as Passive and Active Antibiofouling Coatings: From Fundamental Chemical Development to Performance Evaluation(2012-10-19) Imbesi, PhilipThe overall emphasis of this doctoral dissertation is on the design, synthesis, detailed characterization and application of amphiphilic hyperbranched fluoropolymers (HBFPs) crosslinked with poly(ethylene glycols) (PEGs) in complex polymer coatings as anti-biofouling surfaces. This dissertation bridges synthetic polymer chemistry, materials science and biology to produce functional coatings capable of fouling prevention, demonstrating thermo-controlled healing and acting as a benchmark surface to understand component:property relationships prior to increasing formulation complexities. A two-dimensional array of HBFP-PEG coatings was produced by the co-deposition of uniquely composed HBFPs with varying weight percentages of PEG. Bulk and surface properties were evaluated and assigned to formulation trends. Based on these findings, the most viable candidates were replicated and their fouling responses were assessed against three marine fouling organisms. An active mode of biofouling resistance was covalently grafted onto the surface of HBFP-PEG. The presentation of the settlement-deterrent molecule noradrenaline (NA) works in tandem with the highly-complex surface, to act as a dual-mode, anti-biofouling coating NA-HBFP-PEG. Secondary ion mass spectrometry (SIMS) was employed to quantify the extent of NA substitution. Biological assays against oyster hemocytes confirmed the activity of the grafted NA and cyprid settlement assays supported that the overall anti-biofouling ability of NA-HBFP-PEG was increased by 75%. Thermally-reversible crosslinks were installed as healable units throughout the framework of the networks, with the goal of generating coatings that could possess a greater resistance to mechanical failure. Small molecule and linear polymer models were probed by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) to demonstrate the controlled reversibility of the crosslinks. Optical microscopy was employed to visualize surface scratch healing and fluorescence microscopy was used to identify the adsorption behavior of fluorescently-labeled proteins. A benchmark, anti-biofouling surface was generated through thiol-ene crosslinking of a linear fluoropolymer with pendant alkenes (LFPene) with pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). Core constituents were evaluated spectroscopically and surfaces of LFPene-PETMP, along with two model surfaces that largely expressed a single component, were analyzed to understand how individual elements and blending contributed to the physical, mechanical and anti-biofouling properties to generate a performance baseline to compare against future generations.Item Continuous manufacturing of direct methanol fuel cell membrane electrode assemblies(2010-12) Koraishy, Babar Masood; Wood, Kristin L.; Meyers, Jeremy P.; Manthiram, Arumugam; Bourell, David L.; Jensen, DanielDirect Methanol Fuel Cells (DMFC) provide an exciting alternative to current energy storage technologies for powering small portable electronic devices. For applications with sufficiently long durations of continuous operation, DMFC’s offer higher energy density, the ability to be refueled instead of recharged, and easier fuel handling and storage than devices that operate with hydrogen. At present, materials and manufacturing challenges impede performance and have prevented the entry of these devices to the marketplace. Higher-performing, cost-effective materials and efficient manufacturing processes are needed to enable the commercialization of DMFC. In a DMFC, the methanol-rich fuel stream and the oxidant are isolated from one another by a proton-conducting and electrically insulating membrane. Catalysts in the electrodes on either side of the Membrane Electrode Assembly (MEA) promote the two simultaneous half-reactions which allow the chemical energy carried in the fuel and oxidant to be converted directly into electricity. The goal of this research effort is to develop a continuous manufacturing process for the fabrication of effective DMFC MEAs. Based on the geometry of the electrode and materials used in the MEA, we propose a roll-to-roll process in which electrodes are coated onto a suitable substrate and subsequently assembled to form a MEA. Appropriate coating methods for electrode fabrication were identified by evaluating the requirements of continuous manufacturing processes; an appropriate set of these processes was then reduced to practice on a custom-designed flexible test bed designed explicitly for this project. After establishing baseline capabilities for several candidate methods, a spraying process was selected and a continuous manufacturing process concept was proposed. Finally, key control parameters of the spraying process were identified and their influence tested on actual MEAs to define optimal operating conditions.Item Developing luminescent nanoprobes for labeling focal adhesion complex proteins and performing combined AFM-TIRF imaging of these conjugates(Texas A&M University, 2008-10-10) Nathwani, Bhavik BharatRecent progress in the field of semiconductor nanocrystals or Quantum Dots (QDs) has seen them find wider acceptance as a tool in biomedical research labs. As produced, high quality QDs synthesized by high temperature organometallic synthesis, are coated with a hydrophobic ligand. Therefore, they must be further processed to be soluble in water and made biocompatible. A process to coat the QDs with silk fibroin, a fibrous protein derived from the Bombyx mori silk worm, is described. Following the coating process, the characterization of size, optical properties and biocompatibility profile of these particle systems is described. In addition, conjugation of the silk fibroin coated QDs to different labeling proteins such as phalloidin and streptavidin is described. Proteins on the surface of ovarian cancer cells (HeyA8) and of cytoskeletal components participating in the formation of focal adhesion complex (FAC), such as F-actin in endothelial cells (HUVECS) were labeled using the bio-conjugated QDs. Various imaging techniques such as epi-fluorescence, TIRF and AFM were used to study the QD labeled cells. Overall the project has produced luminescent nanoprobes that enable the study of FAC formation dynamics and potentially a better in vivo fluorescent marker tool.Item Fluorescent coatings for corrosion detection in steel and aluminum alloys(2010-05) Liu, Guangjuan; Wheat, Harovel Grays; Goodenough, John B.; Kovar, Desiderio; Taleff, Eric M.; Juenger, MariaCoatings are often used as a means of protecting aluminum alloy and steel structures in industry. The assessment of corrosion under these coatings can be challenging. Corrosion sensing coatings can exhibit properties that allow undercoating corrosion to be identified before it can be seen with the naked eye. This would be very advantageous and could potentially result in tremendous savings in time and money when structures undergo routine maintenance. Our work involved the study of corrosion sensing coatings with incorporated fluorescent indicators that can be used to sense the undercoating corrosion on metal substrates. The fluorescent indicator in the coated-aluminum system was a negative indicator, i.e. the indicator in the coating was initially fluorescent and subsequently non-fluorescent due to the reduced pH at the anodic sites of corrosion. The fluorescent indicator in coated-steel system was positive, in the sense that the coating changed from non-fluorescent to fluorescent over the cathodic areas due to increased pH. The corrosion sensing coating was composed of commercial epoxy-polyamide and the indicator: 7-amino-4-methylcoumarin (7-AMC) for the coated-aluminum alloy system and 7-diethylamino-4-methylcoumarin (7-DMC) for the coated-steel system. The feasibility of using 7-AMC for sensing early undercoating corrosion was demonstrated by using fluorescent observations, Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) tests. EIS results estimated that with continuous immersion the undercoating corrosion occurred within 24 hours after immersion in the salt solution. When corrosion occurred, the corrosion was invisible under natural light. However, small spots appeared in the fluorescent image, changing from initially fluorescent to non-fluorescent where the anodic sites were identified by SEM and EDS. In other words, the fluorescent indicator could sense the early undercoating corrosion, although blistering can be a competing mechanism associated with corrosion under some conditions. The sensitivity of the 7-AMC corrosion detection system was tested by applying anodic current to the metal and measuring the charge at which fluorescence quenching was detected. The critical charge for a detectable pit under the coating was approximately 2x10⁻⁵ C, which implied a critical radius of a single corrosion spot or set of spots of approximately 10 [mu]m. The fluorescent properties of 7-AMC, its effect on the protectiveness, its sensitivity to pH and its concentration in the coating are explored as well. Fourier transform spectroscopy (FTIR) was used to characterize the structure of the coating with and without 7-AMC. The results suggested that there is no structure change occurring after adding 7-AMC into the coating. Fluorescence behavior, electrochemical behavior, microscopic evidence, and visual observations of coated steel specimens with 7-DMC are compared based on exposure to saltwater conditions. Some of the challenges associated with the use of these types of coatings will be presented. This includes the interference from the increased production of ferrous and ferric ions. All of this information is aimed at the development of corrosion sensing coatings that can reveal undercoating corrosion before it is visible to the naked eye.