Yes / Reverse roll coating is probably the most widely used coating operation, yet its full potential has not been exploited as it is shown in this paper which considers operation with a negative gap. We demonstrate through a wide range of experimental data that such operation can yield very thin and stable films with no ribbing or cascade instabilities when low viscosity fluids are used. Typically, stable film thickness less than 5μm can be obtained at speeds up to 150 m/min when a rubber roller is used at -100 μm gap with fluids of viscosity in the range 10-200 mPa.s. These film thicknesses can be made to decrease further down to 1 or 2 microns with a judicious choice of speed ratios (applicator to metering roller) and rubber hardness. Such new findings make this simple coating method an attractive roll to roll technique for application in the newer coating technologies, such as in the production of solar cells and plastic electronics. The data obtained in this study have been underpinned by a model based on the classical lubrication theory, well developed for such flow situations. Essentially it is shown that the film thickness non dimensionalised with respect to the set negative gap is controlled through a single parameter, the elasticity number Ne which combines all the operating parameters. Of course, this flow problem has complexities, particularly at high speed ratios and at zero gap so the data obtained here can serve as a basis for more comprehensive modelling of this classical fluid mechanic problem. / Films R&D Centre of Toyobo Co. Ltd., Otsu, Japan and the Thin Films Research Group of the University of Bradford, UK.

Yes / Tensioned web-roll coating is widely used but has surprisingly received little research attention. Here, a new semi-empirical model that predicts film transfer from applicator roller to web is developed and tested against data collected from a pilot coating line. The film transfer is found to vary linearly with web to applicator speed ratio S. Flow stability investigations revealed three types of defects: rivulets, air entrainment due to dynamic wetting failure and cascade, occurring at different values of S and capillary number Ca. Rivulets occurred at Ca< 0.4 and S> 0.71-0.81, air entrainment at Ca>0.4 and S>0.71-0.83 and cascades at S>1.1 for Ca up to 6. Web speeds at which dynamic wetting failure occurred were, for the same Ca, comparatively higher than those that occur in dip coating. The data show that such hydrodynamic assistance is due to the coating bead being confined, more so with increasing web wrap angle β. / The authors acknowledge the support of the Films R&D Centre of Toyobo Co. Ltd., Otsu, Japan and of the Thin Liquid Films Research Group of the University of Bradford, UK.

Thin film coatings of (Cao.6Mg0.4)Zr4(P04)6 (CMZP) and Mg stabilized AhTiOs ( Mg-Ah Ti05 ) on dense SiC substrates were investigated using sol-gel coating techniques. The thickness and quality of both CMZP and Mg-Ah Ti05 coatings were found to depend on the solution concentration and lift rate. Double coatings were applied to obtain homogeneous and crack-free coatings. The quality of double coatings was influenced by different first and second coating thickness. The CMZP coated samples were fired in controlled atmospheres to have the pure CMZP phase. Unhydrolyzed solution of Mg-AhTiOs was utilized instead of hydrolyzed solution to improve the quality of Mg-AhTiOs coatings. Aging process was found to improve the quality of CMZP and Mg-Ah TiOs coatings. SiC samples coated with CMZP and Mg-Ah TiOs exhibited good thermal shock resistance and greatly improved the high temperature alkali corrosion resistance. / Master of Science

The corrosion protection service life extension provided by epoxy-coated reinforcement (ECR) was determined by comparing ECR and bare bar from 10 bridge decks built between 1981 and 1995. The objective was to determine the corrosion protection service life time extension provided by ECR field specimens with various degrees of coating adhesion: disbonded, partially disbonded, and wholly bonded coatings. The size and length distributions of cracks in Virginia bridge decks were investigated to assess the frequency and severity of cracks. Correlation of cracks with chloride penetration was used to characterize the influence of cracking on deck deterioration. Cracks influence the rate of chloride penetration, but the frequency and width distributions of cracks indicate that cracks are not likely to shorten the overall service life of most bridge decks in Virginia. Altogether, 141 drilled cores, 102 mm (4 inches) in diameter, were employed in this study. For each of the decks built with ECR, 10 to 12 cores were drilled through a top reinforcing bar adjacent to the previous study core locations. In addition, approximately 3 cores were drilled through a top reinforcing bar at a surface crack location. Laboratory testing involved nondestructive monitoring using advanced electrochemical techniques to periodically assess the corrosion state of the steel bars during cyclic exposure to chloride-rich solution over 22 months of treatment. Time of corrosion initiation and time of cracking (where applicable), as well as chloride content of the concrete before and after treatment, were used in the analysis. Less than 25 percent of all Virginia bridge decks built under specifications in place since 1981 is projected to corrode sufficiently to require rehabilitation within 100 years, regardless of bar type. The corrosion service life extension attributable to ECR in bridge decks was found to be approximately 5 years beyond that of bare steel. / Ph. D.

Novel poly(imide siloxane) copolymers were prepared and developed as high performance fiber coatings. These copolymers were synthesized and characterized extensively as a function of chemical composition. The polyimides were then utilized to coat prototype fibers which were subsequently evaluated regarding thermal stability, thermal behavior, and hydrophobicity. The polymer series included poly(imide siloxane)s which were prepared in two steps, the first involving the generation of soluble poly(amic acid} intermediates which were then cyclodehydrated by heating in a coamide solution, at temperatures ranging from 140 to 170°C, resulting in soluble polymer which exhibited excellent thermal and mechanical properties. Because of the different nature of the imide and siloxane, a two phase microstructure developed at relatively low block molecular weight. X-ray photoelectron spectroscopy (XPS) and contact angle measurements indicated that the surface of the copolymer films was dominated by siloxane. A series of coating solutions was prepared, controlling the solution concentration, solvent, and viscosity. Polybenzimidazole and Kevlar aramid multifilament yarns were immersion coated, dried, and evaluated. Due to the surface segregation of siloxane, these coated fibers advantageously displayed lower moisture sorption as measured in three environments of different humidities. Thus, the coating acted as a hydrophobic barrier. These coated fibers were also evaluated by thermogravimetric analysis (TGA) which displayed that the dynamic thermo-oxidative stability was improved. Finally, thermal expansion coefficients were measured in order to determine coating integrity or matrix/resin integrity under thermal stress. / M.S.

Direct measurements of surface temperatures produced during fretting contact are an unknown area in the discipline of tribology; in addition, the possible effects of such temperatures on the behavior of protective anti-fretting coatings (e.g., polymeric) have never been investigated. An oscillating contact device was designed and built to study fretting contact behavior in tribological processes. The contact geometry consisted of a stationary spherical test specimen loaded against a vibrating sapphire disk driven by an electromagnetic shaker. Surface temperatures generated by frictional heating were measured during fretting contact using an infrared microscope. A photo/video technique was developed to view the fretting contact interface during an experiment and to measure the size and distribution of real area(s) of contact. The effects of size and distribution of the areas on the experimental surface temperatures for polymer-coated steel spheres-on- sapphire were investigated. Archard's theoretical model was also modified to account for multiple contact areas, and the calculated surface temperatures were compared to the experimental results. Polymeric coatings - including polystyrene (PS), polymethylmethacrylate (PMMA), polysulfone (PSO), polyvinylchloride (PVC), and polyvinylidenechloride (PVDC) were studied at a given load (20 N), frequency (150 Hz), amplitude (100 JLm), and film thickness (55 p.m). The surface temperatures generated were generally low and below the glass transition temperatures of the rigid polymers studied. The magnitude of the surface temperatures was found to be particularly dependent on the size and distribution of real area(s) of contact. The most extensive studies were performed using polystyrene coatings. Effects of load, frequency, amplitude, and film thickness on surface temperature rise and the size and distributions of real area of contact were examined. In addition, uncoated steel specimens were studied under various loads and fretting amplitudes. The observed formation of iron oxide at low surface temperature (60°C) tribologica1 experiments was explained in terms of exoelectron emission. There were considerable differences observed in the behavior of polymeric coatings under various fretting conditions. The fretting behavior of the coatings was explained in terms of mechanical and thermo-elastic effects. Thermo-elastic predictions of size distributions of real contact areas (patches) showed good agreement with the observed photo/video studies. A mechanism was proposed for tribological behavior and fretting protection of polystyrene coatings. / Ph. D.

The synthesis of epoxide containing block and alternating copolymers has been investigated in this research. Poly(ethylene oxide-2-ethyl-2-oxazoline) (PEO) copolymers have been synthesized with poly(ethylene oxide) macroinitiators ranging from O.75K-40K. Monohydroxy functionalized PEO oligomers have been synthesized with potassium tert-butoxide as an initiator in tetrahydrofuran, and in the bulk. The PEO oligomers were reacted with 4-(chloromethyl) benzoyl chloride to yield a 4-(chloromethyl) benzoate functionalized PEO oligomer quantitatively. This oligomer was further reacted in the melt with sodium iodide to result in 4-(iodomethyl) benzoate functionalized PEO oligomers. The iodo adduct (macroinitiator) initiated the polymerization of 2-ethyl-2-oxazoline, the second block of the diblock copolymer. The formation of the poly ( ethylene oxide-2-ethyl- 2-oxazoline) copolymer resulted in materials ranging from 20 - 80 weight percent poly(2-ethyl-2-oxazoline) (PEOX). These materials were water soluble with PEOX as a strong hydrogen bonding block in the copolymer. The diblock copolymers may have potential uses in particle stabilization, and coating applications. / Ph. D.

A simple adhesion test method is proposed to provide estimates of the debond toughness of adhesive bonds. Notched coating adhesion (NCA) specimens consist of single substrates coated with thin layers of adhesive. The coating is notched to induce initial debonds, and the specimen is then loaded in a manner to produce tensile stresses in the coating. The substrate strain at which the coating debond propagates is then used to determine the critical strain energy release rate. Yielding of the substrate is permitted, and does not complicate the calculations. The specimen geometry results in a mode mix which drives the debond to the interface, thus obtaining a measure of interfacial behavior. Because of the geometry and testing method, the technique is simple, inexpensive and may be conducted quickly. The properties of the coating and the residual stresses of the bond must be known to predict the bond strength. Since accurate data on these properties are not always readily available, the test may be limited as a method to screen adhesive systems. Besides being a screening test, the NCA can be used as an accelerated test to study the durability of adhesive bonds. NCA specimens reach moisture equilibrium quickly because of the short diffusion path. By significantly reducing the amount of time needed for the adhesive/substrate interface to reach equilibrium moisture conditions, the time required to obtain estimates of performance in humid environments is greatly reduced. If one assumes that moisture at the interface is the cause of bond degradation, these simple tests offer the potential to rapidly estimate the durability of a given adhesive/substrate system. Accelerated durability studies were conducted on model steel/epoxy systems, and the results were compared to the results for double cantilever beam tests. / Master of Science

Over the past decade, fiber optic strain sensors have begun to transition from use in laboratory research to commercial sector applications. This transition is somewhat hindered due to the high cost associated with many optical components required for fiber optic-based sensing systems. Multiplexing systems for fiber optic sensors are one approach to reducing the per-channel cost of fiber optic sensor implementation, however, in many applications, on-line monitoring of sensor elements is not required and the periodical addressing of sensor elements is acceptable. Commercially available fiber optic strain sensor systems are now available which support periodical sensor addressing by providing absolute information about the strain state of the sensor. A post-damage inspection fiber optic sensor design which employs a thick metal coating to retain information regarding the strain history of a sensor is demonstrated. Additionally demonstrated is a corrosion sensing technique which exploits the residual strain retention of the post-damage inspection sensor. Finally, the temperature sensing properties of the metal-coated sensor is investigated. / Master of Science

A novel material, (Ca_0.6,Mg_0.4)Zr₄(PO₄)₆ (CMZP), was evaluated as a weak interface coating for SiC/SiC composites. A procedure was developed to put down uniform and crack-free CMZP coatings on Nicalon cloth and tows using sol-gel and metal organic deposition (MOD). The coated Nicalon cloth samples and tows were infiltrated with SiC matrix using Chemical Vapor Infiltration (CVI). Bars were cut for flexure testing from the infiltrated composite containing Nicalon cloth samples that had been coated using sol-gel. These composites failed gracefully, 1.e., there was fiber pullout and debonding probably at the matrix-coating interface. Minicomposites that contained tows coated using MOD were too weak to be tested for tensile strength. This necessitated the deposition of a thin (~ 30 nm) layer of carbon both on the tows before depositing CMZP coating to protect the fibers as well as on the CMZP coating to protect the coating. Minicomposites that contained these tows, coated using sol-gel and MOD, demonstrated extensive pullout and debonding. The composite behavior could not have been due to the carbon alone as there was very less (~ 60-80 nm) present. Thus, the CMZP coating was responsible, probably in addition to the carbon layers, for the composite behavior. / Master of Science