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Coatings play a pivotal role in everyday life and across various industries. They offer protection, corrosion resistance, insulation, optical improvements, aesthetics, etc. This study investigates the design, fabrication, characterization and evaluation of surface coatings in two areas: antimicrobial activity and fast evaporation. The COVID-19 pandemic underscored the necessity for coatings that mitigate microbial transmission through surfaces, alleviating both contagion and personal fears. The first part of this study presents the design, development, and evaluation of antimicrobial coatings that efficiently inactivate 99.9% of SARS-CoV-2 virus and kill more than 99.9% of pathogenic bacteria such as Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Pseudomonas aeruginosa within one hour. Prioritizing rapid infectivity reduction, we designed and fabricated several coatings using silver oxide (Ag2O), cupric oxide (CuO), and zinc oxide (ZnO) particles as active ingredients. Applying small quantities of micron-sized opaque particles onto a surface yields a transparent film. Although Ag2O particles are inherently opaque, they possess potent antimicrobial properties. Consequently, incorporating small quantities of Ag2O into the coating results in the desired antimicrobial activity while maintaining transparency. Transparent antimicrobial coatings are a necessity for applications such as touchscreens, offering the benefit of reducing disease transmission while maintaining the aesthetic appeal of surfaces. We employed a variant of the Stöber process to bind Ag2O particles to the substrate using a silica matrix. To improve this coating method, we employed room-temperature spin-coating of a suspension of Ag2O/sodium silicate solution on the substrate, eliminating reactions with toxic chemicals in Stöber process and subsequent heat treatment. Two key features of the improved coating are its high robustness and its capability to kill 98.6% of Clostridioides difficile endospores in 60 minutes. On the other hand, CuO and ZnO particles exhibit mild antimicrobial properties; thus, their activity could be enhanced by a porous coating. When an infected droplet lands on such a coating, it is imbibed into the porous structure, where diffusion distances are smaller, and there is a larger active area to inactivate the virus or kill the bacteria. Furthermore, porosity facilitates faster droplet drying, leading to the concentration of cupric and zinc ions in the droplet, which are designed to be toxic to microbes. The second major topic of this thesis is the development, and evaluation of porous coatings for fast evaporation. At low Bond numbers, droplet evaporation is slow on an impermeable surface. We investigated whether application of a thin, porous coating leads to faster droplet evaporation. The droplet will imbibe quickly, but progress normal to the interface will be limited to the thickness of the coating. Therefore, the liquid will spread laterally into a broad disk to expose a large liquid–vapor interface for evaporation. As a result, the evaporation of a droplet is enhanced by a factor of 7–8 on the thin porous coatings. Factors such as coating thickness, pore size and distribution, and the contact angle of the coating, as well as ambient conditions like temperature and relative humidity, could affect the droplet evaporation rates by modifying the droplet's imbibition process and the evaporation driving force. While decreasing the coating thickness and increasing pore size and distribution promoted evaporation, the impact of contact angle is insignificant. Confocal microscopy observations of a coating composed of particles with varying sizes depicted liquid migration along the top of the coating and the edges of the interface. We developed and validated an equation to estimate the rate of evaporation. The rate correlated with the radius of the imbibition area, with higher temperatures and lower humidity further augmenting evaporation. / Doctor of Philosophy / Coatings serve as integral components in various industries and everyday settings, offering multifaceted benefits such as protection, aesthetic enhancement, and functional properties. This study investigates the design, fabrication, and evaluation of two types of surface coatings; coatings that reduce microbes transmission (antimicrobial coatings) and coatings that expedite evaporation. The COVID-19 pandemic underscored the necessity for coatings that mitigate microbial transmission through surfaces, alleviating both contagion and personal fears. The first part of this study presents the design, development, and evaluation of coatings that efficiently reduce 99.9% of COVID-19 virus and kill more than 99.9% of dangerous bacteria that can be found in hospital settings. Prioritizing rapid killing of bacteria, we designed and fabricated several coatings using metal oxides. In particular, we used silver oxide (Ag2O), cupric oxide (CuO), and zinc oxide (ZnO) particles as active ingredients. Applying small quantities of fine-sized opaque particles onto a surface yields a transparent film. Although Ag2O particles are inherently opaque, they possess potent antimicrobial properties. Consequently, incorporating small quantities of Ag2O into the coating results in the desired antimicrobial activity while maintaining transparency. Transparent antimicrobial coatings are a necessity for applications such as touchscreens, offering the benefit of reducing disease transmission while maintaining the aesthetic appeal of surfaces. A chemical reaction was used to produce a glass matrix to bind Ag2O particles to the solid, but this method required heating and toxic chemicals. So we developed a second methods that eliminated these two disadvantages. On the other hand, CuO and ZnO particles exhibit milder antimicrobial properties; thus, their activity could be enhanced by a porous coating. These coatings function as large reservoirs of antimicrobial agents for trapping and deactivating pathogens, while facilitating rapid droplet evaporation through enhanced wicking and porous structure. The second part of this study elucidates the mechanisms underlying accelerated droplet drying as a result of the application of thin, porous coatings. The speed of drying is slow for small droplets on flat surfaces. However, when a droplet is placed on a porous coating, it will be wicked quickly and spread through the porous coating to create a large area for evaporation. As a result, the speed of drying was increased by a factor of 7–8 on the thin porous coatings. Coating parameters such as thickness, pore size, and distribution, surface energy, as well as environmental factors like temperature and humidity could influence the droplet drying from porous surfaces. Decreasing the coating thickness and increasing pore size and variation in pore size promoted droplet evaporation, whereas the impact of surface energy was found to be insignificant. The rate of drying correlated with the radius of the wetted area, with higher temperatures and lower humidity further augmenting evaporation.

Droplet evaporation and condensation are two important topics of interest, since these two phase-change phenomena not only occur in the cycle of global water, e.g., the formation of rain, fog, dew, and snow in nature, but also play a critical role in a variety of applications including phase-change heat transfer enhancement, surface chemistry and energy system optimization. Especially, in the past two decades, the rapid development of the nature-inspired non-wetting surfaces has promoted the applications of droplet-based phase change phenomena in various scenarios. However, most previous studies focused on the sessile droplets on one flat surface in the open space, and the effects of surface topography, i.e., surface curvature or configurations, on droplet evaporation and dropwise condensation are still elusive. This dissertation aims to explore droplet-based evaporation and condensation in more complex spaces and to elucidate how the surface topography affects the evaporating or coalescing droplet dynamics during these phase-change processes. The coalescence-induced jumping of nanodroplet on curved superhydrophobic surface is modeled via molecular dynamic simulations. As the surface curvature increases from 0 to 2, the corresponding energy conversion efficiency of jumping droplet during the coalescence process could be significantly improved about 20 times. To explain this curvature-enhanced jumping effect, the contact line dissipation, i.e., an important source of energy dissipation in nanoscale, is considered in our scaling energy analysis. And this energy-effective jumping of coalesced droplet could be mainly attributed to the reduction of contact line dissipation due to the decrease of contact line length and contact time on curved surface. As the droplets are confined between two parallel or non-parallel low-energy surfaces, i.e., hydrophobic or superhydrophobic surfaces, with a narrow gap, the total evaporation time of the squeezed droplets would be dramatically prolonged about two times. An ellipsoidal segment diffusion-driven model is established to successfully predict the evolution of contact radius and volume of the squeezed droplets during the evaporation process and to clarify it is the vapor enrichment inside the confined space giving rise to the mitigated evaporation. If two hydrophobic surfaces are configured as non-parallel, the confined droplet inside the V-shaped grooves would be self-transported towards the cusp/corner during the evaporation. Based on our energy and force analyses, the asymmetrically confined droplet would move towards an equilibrium location le, where the Laplace pressure induced force is balanced with normal adhesion force, to minimize its Gibbs surface energy. As le decreases during the evaporation, this equilibrium location would directionally shift towards the cusp, which could be regarded as the origin of this evaporation-triggered unidirectional motion. For the first time, the solvent transport and colloidal extraction could be accurately controlled in a combined manner. / Doctor of Philosophy / Droplet evaporation and condensation are two important topics of interest, since these two phase-change phenomena not only occur in the global cycle of water including the formation of rain, fog, dew, and snow in nature, but also play a critical role in a variety of applications including heat transfer enhancement, surface chemistry, and the energy system optimization. Generally, the droplets in these scenarios are deposited on one flat surface opened to the atmosphere. and the effects of surface topography on droplet evaporation and dropwise condensation are still elusive. This dissertation aims to explore droplet-based evaporation and condensation in more complex spaces and to clarify how the surface curvature or configurations affects evaporating or condensing droplet dynamics accompanying these phase change processes. As the coalesced droplet jumps off the curved superhydrophobic surfaces during dropwise condensation, the corresponding energy conversion efficiency would be significantly improved about 20 times due to the increases of curvature. It is demonstrated that the decrease of contact line length and contact time would give rise to the reduction of contact line dissipation, which should be the main factor driving this energy-effective jumping of the coalesced droplets. As the droplets are confined between two parallel or non-parallel low-energy surfaces, i.e., hydrophobic or superhydrophobic surfaces, with a narrow gap, the total evaporation time of the squeezed droplets would be dramatically prolonged about two times in the small space. An ellipsoidal segment diffusion-driven model is established to successfully predict the evolution of contact radius and volume of the squeezed droplets during the evaporation and to clarify it is the vapor enrichment in the confined space giving rise to the mitigated evaporation. If two hydrophobic surfaces are configured as non-parallel, the confined droplet inside the V-shaped grooves would be self-transported towards the cusp/corner of the structure during evaporation. Based on our energy and force analyses, the asymmetrically confined droplet would move towards an equilibrium location le, where the Laplace pressure induced force is balanced with normal adhesion force, to minimize its Gibbs surface energy. As le decreases in the scale of during the evaporation, this equilibrium location would directionally shift towards the cusp, which could be regarded as the origin of this evaporation-triggered unidirectional motion.

Evaporators employed in the distillation of sea water have scale form on their heat transfer surfaces as calcium carbonate, magnesium hydroxide, and calcium sulfate in 300 to 500 hours of operation. Although the measures directed to overcome the formation of scale in sea water evaporators have been varied, none of these measures have been as successful as desired, and the problem is, therefore, still a major one. In 1947, however, C. A. Hempel, Armour Research Foundation, Chicago, Ill., approached the scale problem of sea water evaporators rationally by saying that if the carbon dioxide content and the pH of sea water could be controlled by either physical or chemical means, that the scale deposition on the heat transfer surfaces would be reduced. By experimentation, Hampel developed a process whereby sea water is heated under pressure for a definite period of time, and then it is released to atmospheric pressure with aeration. This physical pretreatment process removes the carbon dioxide that is evolved from the decomposition and hydrolysis of the carbonate and bicarbonate content of sea water, and thus prevents the formation of insoluble calcium carbonate. The change in alkalinity does, however, cause insoluble magnesium hydroxide to form, but this insoluble material can be readily removed by filtration followed by acidification. Therefore, two of the scale forming salts, calcium carbonate and magnesium hydroxide, have been eliminated by this process. In 1948, both the U. S. Coast Guard and the Bureau of Ships, Navy Department, became interested in this development of Hampel's, and they agreed to design a pretreatment plant for a 4000-gallon per day evaporator in order to evaluate further this process on a large scale basis. Such a plant was designed and constructed at the Norfolk Naval Shipyard, Portsmouth, Va., with the Coast Guard providing the necessary materials and equipment for the pretreatment plant, and the Navy furnishing the materials and equipment for the distilling unit. The Army Engineer's building and sea water facilities that were available at Fort Story, Va., made it a highly desirable location for the testing of the decarbonation and distilling units. So, after all the equipment had been fabricated and hydrostatically tested, it was shipped to Distillation Test Station at Fort Story where it was erected and made operational by Naval Shipyard personnel. In September, 1949, a series of tests were started on this equipment at Fort Story to evaluate the design and construction of the pretreatment plant to decarbonate sea water es a means of reducing the scale in a 4000-gallon per day Grissom-Russell low pressure, double effect Soloshell evaporator. The first test of decarbonation calibration was made to determine the optimum operating conditions of the pretreatment plant which would give the maximum degree of carbon dioxide removal from sea water. The second test was a blank determination of evaporator scale, using untreated feed, by which a comparison could be made with all subsequent tests. The pretreatment plant involved the operation of two pieces of equipment, the feedwater holding tank and the aerator tank. The procedure that was followed in this calibration was essentially this: the sea water was heated to a definite temperature at a specific feed rate, pumped to the feedwater holding tank and retained in this tank for definite periods of time; then the sea water was released to the aerator tank, again held for definite periods of time while being aerated with air, and a sample of sea water analyzed to determine the degree of carbon dioxide that was removed by these conditions. The variables that had their effect on the degree of decarbonation were, therefore, feed temperature, feed rate, feedwater tank holding time, aerator tank holding time, and air rate. The effect of temperature on the degree of decarbonation was that the greater the temperature, the greater the carbon dioxide removal; 250 °F removed 47.5 to 50 per cent, 240 °F removed 38 to 42 per cent, and 228 °F removed 25.2 to 25.8 per cent. The effect of feed rate at 250 °F on the degree of decarbonation was that the smaller feed rate, the greater the carbon dioxide removal; a feed rate of 5.25 gallons per minute removed 42.1 to 52.4 per cent whereas a feed rate of 10.5 gallons per minute only removed 36.6 to 47 per cent. The effect of feedwater tank holding time on the degree of decarbonation et 250 °F and 5.25 gallons per minute feed was negligible since holding times of 25, 45, 66, 86, and 106 minutes removed 50.2 to 54 per cent of the carbon dioxide. In the determination of the effect of aerator holding time on the degree of decarbonation a 250 °F and 5.25 gallons per minute feed, the greater the holding time, at 14 and 28 minutes, the greater the carbon dioxide removal, i.e., 46 end 50 per cent, respectively. The effect of air on the degree of decarbonation at 250 °F, 5.25 gallons per minute feed, and 28 minutes aerator tank holding time, was that it gave the greater degree of carbon dioxide removal, but without air, the effect was that the greater the feedwater tank holding time, the less the carbon dioxide removal. The difference between the two air rates tried was negligible; 5 cubic feet per minute removed 51 to 54 per cent, whereas 20 cubic feet per minute only removed 44 to 52 per cent. With no air, however, a feedwater tank holding time of 25 minutes removed 50.8 per cent, 45 minutes removed 43.5 per cent, 66 minutes removed 39.5 per cent, and 106 minutes removed 38.5 per cent. Therefore, from the results of the calibration, it is concluded that the optimum operating conditions for the pretreatment plant are a feed temperature of 250 °F, a feed rate of 5.25 gallons per minute, a feedwater tank holding time of 25 minutes, an aerator tank holding time of 28 minutes, and an air rate of 5 cubic feet per minute which will remove 50.8 per cent of the carbon dioxide in the sea water. In the blank determination, the feed by-passed the pretreatment plant and went directly to the evaporator, which was operated at a feed rate of 5 gallons per minute, 150 °F, 2.5 pounds per square inch, gage of steam to the first effect, 97 pounds per square inch, gage of steam to the air ejector, 26.5 inches of vacuum, 70 gallons per minute of circulating water, and 1.5-thirty seconds overboard brine density. In 135 hours of operation, 19,400 gallons of fresh water were produced which had a salinity of less than 0.5 grain per gallon. Scale was formed at a rate of 0.23 pound per 1000 gallons of distillate produced, and whose composition wan 91.1 per cent calcium carbonate, 2.6 per cent magnesium hydroxide, 2.7 per cent calcium sulfate hemihydrate, 2.7 per cent silica dioxide, and 1.1 per cent ferric oxide. From the operation of these tests, it is concluded that both the pretreatment plant and the distilling unit operated satisfactorily within the limits of their design. / Master of Science

Dans la littérature, que ce soit pour un explosif secondaire ou un matériau composite, une balance en oxygène (BO) proche de 0% est assimilée à de bonnes performances énergétiques (vitesse de détonation, chaleur de décomposition, etc…). L’objectif majeur de cette thèse est d’améliorer les performances énergétiques d’explosifs secondaires courants (RDX, HMX, CL-20) par l’ajout d’un oxydant (DNA) afin d’obtenir un matériau composite avec une BO de -1%. Le mélange intime de ces deux composés est permis par un procédé d’évaporation flash de spray, utilisé habituellement pour réduire la taille de particules des explosifs. Les matériaux composites ont été cristallisés dans les trois cas avec succès, avec la présence d’explosif submicrométrique et de DNA nanostructuré. Un tel résultat a été permis grâce à une meilleure compréhension du procédé, et en conséquence l’ajustement des conditions expérimentales. L’étude de la réactivité de ces matériaux composites montre dans certains cas une désensibilisation, une diminution de la distance de la déflagration à la détonation, ou encore une augmentation de la vitesse de détonation, comparée aux explosifs correspondants. / In literature, for secondary explosive or composite material, an oxygen balance (OB) close to 0% is often linked to good energetic performances (detonation velocity, heat of decomposition, etc.). The main objective of this thesis is to enhance energetic performances of current secondary explosives (RDX, HMX, CL-20) by adding oxidizer (ADN) to obtain a composite material with an OB of -1%. The spray flash evaporation process, usually used for particle size reduction of explosives, enables to obtain an intimate mixture of these two compounds. Composite materials were successfully crystallized in three cases, resulting of submicrometric explosives and nanostructured ADN particles. These results were obtained thanks to a preliminary study for better process understanding and the optimization of experimental conditions. Reactivity studies show some desensitization, shorter distance from deflagration to detonation, and/or higher detonation velocity, compared to corresponding explosives.

Gao, Xuehua. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 83-96). / Abstracts in English and Chinese. / List of Figures --- p.viii / List of Tables --- p.x / Symbols --- p.xi / Acronyms --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background and Motivation --- p.1 / Chapter 1.2 --- Study Site: Pearl River Basin --- p.3 / Chapter 1.3 --- Study Objectives --- p.4 / Chapter Chapter 2 --- Literature Review --- p.5 / Chapter 2.1 --- Methods for Determining ETa --- p.6 / Chapter 2.2 --- Limitations of Current Studies on ETa --- p.15 / Chapter Chapter 3 --- Methodology and Data --- p.17 / Chapter 3.1 --- Modelling Framework and Procedure --- p.17 / Chapter 3.2 --- Complementary Relationship Models --- p.19 / Chapter 3.3 --- Long-Term Water Balance Models --- p.22 / Chapter 3.4 --- Spatial Interpolation --- p.25 / Chapter 3.5 --- Trend Analysis --- p.26 / Chapter 3.6 --- Meteorological and Hydrological Data Sets --- p.29 / Chapter Chapter 4 --- Estimation of Actual Evapotranspiration --- p.40 / Chapter 4.1 --- Selection of Water Balance Model --- p.40 / Chapter 4.2 --- Selection of Complementary Relationship Model --- p.46 / Chapter 4.3 --- Calibration of Granger & Grey´ةs Model --- p.48 / Chapter 4.4 --- Estimation of A ctual Evapotranspiration --- p.48 / Chapter 4.5 --- Validation of Granger & Grey ´ةs Model --- p.49 / Chapter Chapter 5 --- Spatio-Temporal Variations of Actual Evapotranspiration --- p.50 / Chapter 5.1 --- Annual ETa --- p.50 / Chapter 5.2 --- Seasonal ETa --- p.56 / Chapter 5.3 --- Summary --- p.63 / Chapter 5.4 --- Discussion of the Changing Climatic Factors --- p.64 / Chapter Chapter 6 --- Sensitivity Analysis of Actual Evapotranspiration to Climatic Variables --- p.66 / Chapter 6.1 --- Sensitivity Curves and Sensitivity Coefficients --- p.66 / Chapter 6.2 --- Procedures and Results --- p.61 / Chapter 6.3 --- Implications of Sensitivity Coefficients for Water Resources Management --- p.77 / Chapter Chapter 7 --- Conclusion --- p.79 / Chapter 7.7 --- Summary --- p.79 / Chapter 7.2 --- Conclusion --- p.80 / Chapter 7.3 --- Implication --- p.81 / Chapter 7.4 --- Limitation and Future Work --- p.82 / References --- p.83 / ","