This thesis describes investigations into a number of coating processes using experimental, analytical and computational techniques. The first problem, considered experimentally, is that of reverse roll coating with a liquid reservoir positioned directly above horizontally aligned rollers. Measurements of the film thickness as a function of the height of fluid in the reservoir and speed ratio are presented. When the wetting line is located downstream of the nip, either a decrease in the height of the associated hydrostatic head or an increase in the speed ratio causes a reduction in the thickness of the outgoing film. However, when the wetting line is located upstream of the nip the opposite is found to be true. The bead-break instability in forward meniscus coating is considered both experimentally and analytically. Agreement between predictions from a simple mathematical model of the stable bead and experimentally determined meniscus positions is seen to be excellent. A perturbation hypothesis is used to predict the onset of the bead-break instability, at which the upstream meniscus accelerates rapidly towards the downstream one, so the two collide and the bead collapses. The results from the model compare well with experiments. An outline of a method for using the bead-break instability as a design criterion is also presented. Typically in a slot, blade or knife coater the downstream meniscus is assumed to pin at a corner of the coating device. In chapter 5, a series of experiments and a corresponding computational study, are presented which illustrate that the meniscus can advance up the face of such coating devices (in this case a roll-flat plate system). Reducing the corner angle is seen to reduce the size of the climb region and the associated recirculation at this point at the downstream meniscus. It is also shown that the meniscus can detach from the corner and retreat into the gap, which can in turn give rise to the ribbing instability. An offset gravure coating arrangement is considered in chapter 6. The coating arrangement is split into two areas of study - the offset gravure nip and the kiss coating bead. An experimental investigation of the offset nip with the two rolls vertically aligned and running at the same speed in forward mode reveals two ways in which the metered film thickness can be influenced. Either increasing the nip force by pressing the two rolls together or decreasing the roll speeds causes a reduction in the metered film thickness. At higher speeds the metered film thickness is observed to asymptote to a limiting value, the value of which depends on the gravure pattern. The reverse mode kiss coating bead operating at speed ratios greater than one is also investigated. Experiments reveal that under these conditions, all the fluid is transferred from the roll surface to the web and the two make contact due to the generation of a sub-ambient pressure field within the bead. Two models based on lubrication theory are derived, one assuming an infinitely tensioned web and a second that incorporates the effect of web flexibility. The latter is found to give much better agreement with the experimental data. Finally a perturbation hypothesis is applied to these to models in order to predict the onset of the ribbing instability, both of which are found to give reasonable agreement with the experimental data. Finally, the results of a systematic experimental investigation of reverse mode direct gravure coating is reported, where the web runs directly over a gravure roll surface. This wide ranging parametric study illustrates the effect of the operating parameters on the final film thickness. Key findings are that speed ratio, fluid properties and cell shape and size can significantly influence the final film thickness. For a fixed roll speed it is observed that as the web speed is increased the gravure bead becomes unstable. This results in streaking on the web, and gives an upper limit to the speed ratio.

Evaluation and characterisation of thermal barrier coatings (TBCs) have been conducted correlating microstructure with physical and mechanical properties, to further understand TBC failure mechanisms and performances in this thesis. A modified four-point bending test was employed to investigate the interfacial toughness of atmospheric plasma sprayed TBCs. The delamination of the TBCs occurred mainly within the topcoat. The energy release rate increased from ~50 J/m-2 for as-sprayed conditions to ~120 J/m-2 after annealing at 1150 ºC for 200 hours with a loading phase angle about 42º. Micro X-ray tomography revealed how various types of imperfections developed near the interface and the 3D interface was characterised. Stress measurements by photoluminescence piezospectroscopy (PLPS) and analytical solutions were combined to investigate the local stress around spherically symmetrical portions of a TGO layer formed on Fecralloy. Spherical indenters were used to create curvature with different curvature radii and depths on alloys. The effect of curvature radius on stress was found to be more significant than the depth of local curved area. TGO stress as a function of oxidation time at the curved areas was also discussed. Electron beam physical vapour deposited (EBPVD) TBCs with a β-(Ni,Pt)Al bond coat on CMSX4 substrate were investigated by micro X-ray computed tomography (XCT). The 3D microstructures evolution and damage accumulation were studied. 3D interfacial roughness was calculated and compared to scanning electron microscope image analysis. The calculated interfacial roughness did not change much even after 200 thermal cycles, indicating there was not obvious rumpling in this TBCs sample. Commercial simple and Pt-modified aluminide coatings were studied and compared. Both coatings consisted mainly of β-NiAl phase. Thermogravimetric analysis (TGA) tests indicated that the Pt-modified aluminide coating was much more resistive for oxidation than simple aluminide coating. Instrumented indentation was used to measure the mechanical properties, showing the coatings had similar young’s modulus around 130 GPa while Pt-modified aluminide coating was more ductile and had a higher fracture toughness than simple aluminide coating. The Raman spectra of yttria-stabilised zirconia (YSZ) in the temperature range of 25-1100 ºC were investigated. The peak shift and broadening were carefully analysed. The thermal mismatch stress was found to have a negligible effect on the Raman shift. The dependence can be used to monitor the temperature in YSZ without contact.

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Recent interest in environmentally friendly alternatives to chromate-based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described in this thesis has been aimed at investigating the mechanism of self-healing and active corrosion protection of the new coatings by searching for active components that have migrated from the coating to a controlled defect. The use of glow discharge optical emission spectroscopy (GDOES) has been investigated as a tool for both the generation of a reproducible controlled defect and for elemental depth profiling of the coatings and corroded substrates. Conclusions drawn from the elemental depth profiles have been validated by a range of characterisation techniques including optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and electrochemical techniques. The work has focused particularly on a comparison of hybrid coatings doped with inhibitors encapsulated in nano-containers, as compared with the direct addition of inhibitor species to the coating matrix. The work also investigates the effects of inhibitor addition to sol-gel coatings or primer systems or both, highlighting possible synergistic effects of mixed inhibitor systems (for example, sol-gel coating doped with strontium aluminium polyphosphate (SAPP)) supporting primers doped with benzotriazol (BZT) or mercaptobenzothiazol (MBT). The various coatings have also been studied in the absence of inhibitor species to assess the effectiveness of the coatings as barriers between the substrate and the corrosive environment. This aspect of the study has highlighted minor inhibitive effects of some of the reagents used in the coating formulations and a major inhibitive effect of the nano-containers. The work therefore concludes with recommendations for a possible coating formulation combining the most beneficial elements of the various coatings investigated.

The development of a "cradle-to-cradle" mindset with both material performance during utilization and end of life disposal is a critical need for both ecological and economic considerations. The main limitation to the use of the biopolymers is their mechanical properties. Reinforcements are therefore a good alternative but disposal concerns then arise. Thus the objective of this dissertation is to investigate a biopolymer nanocomposite where the filler is a synthetically prepared layer double hydroxide (inorganic interface); and a biopolymer paper (organic interface) based coating or laminate. The underlying issues driving performance are the packing density of the biopolymer and the interaction with the reinforcement. Since the polyhydroxyalkanoates or PHAs (the biopolymers used for the manufacture of the nanocomposites and coatings) are semicrystalline materials, the glass transition was investigated using dynamic mechanical analysis (DMA) and dielectric spectroscopy (DES), whereas the melt crystallization, cold crystallization and melting points were investigated using differential scanning calorimetry (DSC). Fourier transform infrared (FTIR) spectroscopy was used to estimate crystallinity in the coated material given the low thermal mass of the PHA in the PHA coating. The significant enhancement of the crystallization rate in the PHA nanocomposite was probed using DSC and polarized optical microscopy (POM) and analyzed using Avrami and Lauritzen-Hoffman models. Both composites showed a significant improvement in the mechanical performance obtained by DMA, tensile and impact testing. The degradation and decomposition of the two composites were investigated in low microbial activity soil for the cellulose paper (to slow down the degradation rate that occurs in compost) and in compost. An in-house system according to the American Society for Testing and Materials ASTM D-98 (2003) was engineered. Soil decomposition showed that PHA coating into and onto the cellulose paper can be considered to be a useful method for the assessment of the degradability of the biopolymer. PHA nanocomposite showed enhanced compostability.

Recent commercial developments have created a need for alternative materials and methods for imparting oil/grease resistance to paper and/or paperboard used in packaging. The performance of a novel grease resistant functional coating comprised of polyvinyl alcohol (PVA), sodium tetraborate pentahydrate (borate) and acetonedicarboxylic acid (ACDA) and the application of said coating by means of flexographic press is presented herein. Application criteria is developed, testing procedures described, and performance assessment of the developed coating materials are made. SEM images along with contact angle data suggest that coating performance is probably attributable to decreased mean pore size in conjunction with a slightly increased surface contact angle facilitated by crosslinking of PVA molecules by both borate ions and ACDA.

The general objective of this thesis is to conduct experiments on sphere free-falling in liquid that advance our understanding of the drag reduction on solids moving in liquid by means of lubricating gas layers and attached streamlined air cavities. Part I of the thesis investigates the effect of thin air layers, naturally sustained on superhydrophobic surfaces, on the terminal velocity and drag force of metallic spheres free- falling in water. The surface of 20 mm to 60 mm steel or tungsten-carbide spheres is rendered superhydrophobic by a simple coating process that uses a commercially available hydrophobic agent. By comparing the free-fall of unmodified spheres and superhydrophobic spheres, in a 2.5 meters tall water tank, it is demonstrated that even a very thin air layer (~ 1 – 2 μm) that covers the freshly dipped superhydrophobic sphere, can reduce the drag force on the spheres by up to 80 %, at Reynolds numbers 105 to 3×105, owing to an early drag crisis transition. Part II of the thesis investigates the drag reduction by means of the dynamic Leidenfrost vapor-layer sustained on the surface of heated metallic spheres free-falling in a fluorocarbon liquid, FC-72 (perfluorohexane). In these experiments we employed two tall liquid tanks: a 3 meter tall 14 cm wide tank and a 2 meter tall 20 × 20 cm cross-section tank with a heater device. These tanks are significantly larger than the tanks used in prior studies and allow us to track the extended fall trajectories and to compare the drag on room-temperature no-vapor-layer spheres to that of heated Leidenfrost vapor-layer spheres. Analysis of the extended free-fall trajectories and acceleration, based on the sphere dynamic equation of motion, enables the accurate evaluation of the vapor-layer-induced drag reduction, without the need for extrapolation. We demonstrate that the drag on the Leidenfrost sphere in FC-72, can be as low as CD = 0.04 ± 0.01, or an order of magnitude lower than the values for the no-vapor-layer spheres in the subcritical Reynolds number range. This drag reduction extends into the supercritical Reynolds number range. The analysis method developed herein, to describe the sphere trajectories, can be applied in other related studies. Part III of the thesis examines a recently demonstrated phenomenon of the formation of stable-streamlined gas cavity following the impact of a heated Leidenfrost sphere on a liquid surface or a superhydrophobic sphere on water. The sphere encapsulated in a teardrop-shaped gas cavity was found to have near-zero hydrodynamic drag due to the self-adjusting streamlined shape and the free-slip boundary condition on the cavity interface. Here it is shown that such cavities can be formed following the water impact from a sufficient height of non-superhydrophobic spheres with water contact angles between 30° and 120°. In this case the streamlined cavity is attached just above the sphere’s equator, instead of entirely wrapping the sphere. Nevertheless, this sphere with attached cavity has near-zero drag and predetermined free-fall velocity in compliance with the Bernoulli law of potential flow. Last, the effect of surfactant addition to the water solution is investigated. The shape and fall velocity of the sphere with streamlined cavity formation were unaffected by the addition of low-surface-modulus synthetic surfactants, but was destabilised when a solution containing high-surface-modulus surfactants, such as soaps were used.

Biological fouling occurs everywhere in the marine environment and is a significant problem for marine vessels. Anti-fouling coatings have been used effectively to prevent fouling; however, these coatings harm non-targeted sea-life. Fouling-release coatings (FRC) appear to be an alternative way to combat fouling. FRC do not necessarily prevent the settlement of marine organisms but rather allow their easy removal with application of shear to the coatings surface. These coatings must be non-toxic, non-leaching, have low surface energy, low modulus, and durability to provide easy removal of marine organisms. Here the goal is to develop FRC based on thermosetting siloxane-polyurethane, amphiphilic polyurethane, and zwitterionic/amphiphilic polyurethane systems. A combinatorial high-throughput approach has been taken in order to explore the variables that may affect the performance of the final coatings. Libraries of acrylic polyols were synthesized using combinatorial high-throughput techniques by either batch or semi-batch processes. The design of the experiments for the batch and semi-batch processes were done combinatorially to explore a range of compositions and various reaction process variables that cannot be accomplished or are not suitable for single reaction experiments. Characterization of Rapid-GPC, high-throughput DSC, and gravimetrically calculated percent solids verified the effects of different reaction conditions on the MW, glass transition temperatures, and percent conversion of the different compositions of acrylic polyols. Coatings were characterized for their surface energy, pseudobarnacle pull-off adhesion, and were subjected to bioassays including marine bacteria, algae, and barnacles. From the performance properties results the acrylic polyol containing 20% hydroxyethyl acrylate and 80% butyl acrylate was selected for further siloxane-polyurethane formulations and were subjected to the same physical, mechanical, and performance testing. Amiphiphilic copolymers based on PDMS molecular weight and the addition of PEG based polymer blocks on the properties of acrylic-polyurethane coatings were explored. The key properties screened were surface energy, determined by contact angle measurements using water and methylene iodide, dynamic water contact angle, and pseudobarnacle adhesion properties. The data from all of the biological assays indicates that the novel coatings were able to resist fouling and have low fouling adhesion for the broad variety of fouling organisms tested.

Scratch recovery is a desirable property of many polymer systems. The reason why some materials have demonstrated excellent scratch recovery while others do not has been a mystery. Explaining the scratch resistance based upon the hardness of a material or its crosslink density is incorrect. In this thesis, novel polymers were tested in an attempt to discover materials that show excellent scratch recovery - one of the most important parameters in determining the wear of a material. Several hypotheses were developed in an attempt to give an accurate picture of how the chemical structure of a polymer affects its scratch recovery. The results show that high scratch recovery is a complex phenomenon not solely dependent upon the presence of electronegative atoms such as fluorine.