Non-wetting surfaces mainly categorized into superhydrophobic (SHS), lubricant-infused (LIS) and solid-infused surfaces (SIS), by virtue of their superior water repellant properties have wide applications in several energy and environmental systems. In this dissertation, the role of non-wetting surfaces toward the enhancement of condensation effectiveness is analyzed by taking into consideration the tube side and shell side individual interfacial energy transport processes namely, drag reduction, convection heat transfer enhancement, fouling mitigation and dropwise condensation heat transfer. First, an analytical solution is developed for effective slip length and, in turn, drag reduction and friction factor on structured non-wetting surfaces. Secondly, by combining the solution for effective slip length on structured non-wetting surfaces and the fractal characterization of generic multiscale rough surfaces, a theoretical analysis of drag reduction, friction factor, and convection heat transfer enhancement is conducted for scalable non-wetting surfaces. Next, fractal representation of rough surfaces is used to theoretical derive the dropwise condensation heat transfer performance on SHS and novel SIS surfaces. The aspect of dynamic fouling mitigation properties of non-wetting surfaces is explored by conducting systematic experiments. Using Taguchi design of experiments, this work for the first time presents a closed formed relationship of fouling mitigation quantified in terms of asymptotic fouling resistance with Reynolds number, foulant concentration and viscosity of the infusion material that represents the different surface types in a unified manner. Furthermore, it was observed that LIS and SIS offer excellent fouling mitigation compared to SHS and conventional smooth surfaces, however only SIS owing to the presence of solid-like infusion materials is observed to be robust for practical applications. / Doctor of Philosophy / Inspired by the naturally occurring water repellant lotus leaf and pitcher plant, metallic surfaces have undergone engineering modifications to their native wetting properties. By generating roughness features ranging from nanometer to micrometer length scales, subjecting them to low surface energy treatments and by choosing an appropriate water repellant infusion material, the water repellant properties seen on lotus leaf and pitcher plant can be engineered. Such water repellant (non-wetting) surface fabrication methods are widely available in the literature however very few are scalable to surface types (e.g. copper, aluminum etc.), surface size (millimeters to meters) and shape (plain, curved, inside of tubes etc.). In this work, considering scalable fabrication methods such as electrodeposition and chemical etching, a systematic analysis is conducted on enhancement of four interfacial processes that are a part of many industrial applications. First, the extent of water repellency by structured non-wetting surfaces for the flow of fluid (water) quantified in terms of effective slip length of flow is analytically derived. Using this theory and a self-similar (fractal) nature of the more generic rough surface designs, a theoretical analysis into the drag reduction, convection heat transfer enhancement on non-wetting surfaces is conducted. Next, using the fractal nature of the rough superhydrophobic surfaces (SHS) a theoretical investigation into dropwise condensation performance is used to derive bounds on condensation heat transfer enhancement. Through systematic experimental investigations, it is shown that a solid-infused surface (SIS) and lubricant-infused surfaces (LIS) which, respectively, incorporate a polymer and a slippery lubricant in the interstitial region of metallic asperities, exhibit superior dynamic mineral fouling mitigation performance compared to SHS and conventional smooth surfaces. In addition, it is demonstrated that SIS is a far robust and durable choice when compared to LIS for use in the long run.

Medical implants constitute an essential advancement in modern medicine, often restoring or replacing functionality to failed organs. Whether a medical implant is temporary or permanent, medical implants carry the risk of implant failure due to an infection. Implant-associated infections (IAI) are challenging to treat and often result in increased medical costs, prolonged hospital stays, implant failure, and, in some instances, severe infections that can lead to amputations, sepsis, or mortality. Eradicating an IAI can be challenging since bacteria can form biofilms on the implant’s surface. The biofilms comprise an extracellular matrix protecting the bacterial cells against systemic antibiotics and the host’s immune system. Treating an IAI usually entails a broad range of antibiotic treatment and surgical procedures for tissue debridement or implant replacement. For the reasons stated above, scientists and engineers continue to develop technologies to protect the surface of medical implants against infections. Amongst the new technologies, Liquid-Infused Surfaces (LIS) are renowned for their repellent and anti-fouling properties created by tethering a stable liquid layer onto the surface. However, many challenges remain to adopt this technology for implantable devices. For instance, the high repellent properties can hinder implant-tissue interaction and discourage proper integration with the body. Furthermore, the stable liquid layer is contingent on the surface properties of the coated material. In other words, the long-term stability of these coatings may be compromised if the surface chemistry is covered by biological processes such as biofilm formation from adherent bacteria. This thesis aims to expand on the applications of LIS coatings and enhance their properties for implantable materials. This thesis reviews different types of antibiotic surface coatings and further examines LIS technologies as a viable antibacterial coating for medical implants. Then, three novel multifunctional LIS coatings are presented. The first developed coating enhanced the antibacterial properties of the coating by adding bactericidal agents within the LIS coating. The developed antibiotic liquid-infused coating not only repelled bacteria but also lysed bacteria upon contact. The second coating was designed to promote tissue integration. This multifunctional coating promoted cell deposition and proliferation while remaining repellent toward bacteria, while the conventional LIS coating displayed poor cell availability. Lastly, a collagen-bacteriophage conjugated liquid-infused coating was developed to promote tissue integration while having a two-tier layer of antibacterial protection. This coating was tested in a mouse sepsis model and prevented mortality of all mice, with other groups as high as 90% mortality. These coatings constitute essential steppingstones to bring LIS technology to medical implants. / Dissertation / Doctor of Philosophy (PhD) / Implant-associated infections (IAI) remain a significant problem in modern medicine. IAIs are challenging to treat and often result in increased medical costs, prolonged hospital stays, implant failure, and, in some instances, severe infections that can lead to sepsis or mortality. For these reasons, new technologies have been developed to protect the surface of medical implants against infections. Amongst the new technologies, Liquid-Infused Surfaces (LIS) are renowned for their repellent and anti-fouling properties created by tethering a stable liquid layer onto the surface. This thesis aims to expand on the applications of LIS coatings and enhance their properties for implantable materials. This thesis reviews different types of antibiotic surface coatings, examines LIS technologies, and presents three novel multifunctional LIS coatings. The newly developed coatings enhance the LIS coatings through the addition of antibacterial properties and biomolecules to promote tissue integration.

The goal of this study is to quantify the transient performance of microfabricated superhydrophobic surfaces when used in underwater applications. A mathematical framework is developed and used to predict the stability, longevity, and drag reduction benefits of submerged superhydrophobic surfaces with two- or three-dimensional micro-textures. In addition, a novel design is proposed to improve the drag-reduction benefits of lubricant-infused surfaces, by placing a layer of trapped air underneath the lubricant layer. The new design is referred to as lubricant–infused surfaces with trapped air, and it is designed to eliminate the long-lasting longevity problem of submerged superhydrophobic surfaces. The effectiveness of liquid-infused surface with trapped air design was examined via numerical simulation, and it was found to outperform its liquid-infused surface counterpart by about 37%.

Lorsqu'un liquide mouillant touche un solide, on observe un ménisque de taille millimétrique. Si le solide est rugueux à une échelle submillimétrique, le liquide peut progresser le long des aspérités sur une distance qui est potentiellement illimitée si le solide est horizontal. Nous modélisons la rugosité avec des piliers cylindriques et montrons que quelques cylindres seulement suffisent à transporter et guider précisément un liquide. Nous étudions la dynamique macroscopique et microscopique de l'invasion. Nous examinons ensuite combien de liquide s'accumule dans une variété de textures et proposons un nouveau type de détergence pour extraire le liquide de la rugosité. Nous prenons aussi la gravité en compte et l'utilisons d'abord pour démontrer que plusieurs fronts liquides peuvent être observés simultanément dans des porosités multi-échelles. Nous nous intéressons enfin aux ponts capillaires millimétriques et nous dédions notre dernier chapitre à leur dynamique de croissance radiale. / When a wetting liquid contacts a solid, we observe a liquid meniscus of millimetric size. If the solid is rough at a submillimetric scale, the liquid may progress along the asperities for a potentially unlimited distance if the solid is horizontal. We model the roughness with a regular texture and show that a low number of surface features is sufficient to transport and precisely guide a liquid. We study the macroscopic and microscopic dynamics of the invasion. We examine then how much liquid accumulates in a variety of texture and propose a new kind of detergency to remove the liquid from the roughness. We also consider the influence of gravity and use it to demonstrate that multiple liquid fronts can be observed simultaneously in porosities of different scales. Then we turn our attention to millimetric capillary bridges and dedicate our last chapter to explain their dynamics of radial growth with the Cox-Voinov model.

Beams are ubiquitous in our everyday life and can be found in a variety of length scales, from large supports of buildings to carbon nanotubes. Similarly, bubbles can also span a variety of scales, ranging from tiny bubbles in a glass filled with champagne to the giant soap bubbles formed by artists to attract crowds. Yet, the behavior of beams and bubbles can often occur so fast that the dynamics go unnoticed. This dissertation aims to understand the mechanics of beams and bubbles in four different examples. We combine table-top experiments with mathematical models to predict how each system will behave when exposed to different extreme conditions. We start by examining the retraction of a rubber band once it has been stretched and released. This process is similar to plucking a string, where the dynamics are governed by tensile and inertial forces, resulting in a trapezoidal shape during retraction. However when a rubber band is stretched and released, a region of high-curvature develops. Our experiments and mathematical model highlight that bending forces can be significant and give rise to a curved self-similar shape to the retracting rubber band. The next example involves the competition of surface tension and twisting on a flexible rod. Most studies in the field of elasto-capillarity have focused on how surface tension can bend an elastic structure, leaving the possibility of twisting unexplored. Here we utilize particles with discrete wettabilities -- or Janus particles -- at liquid interfaces that can be used to twist a flexible cylinder. The third system is focused around the spreading behavior of bubbles on submerged surfaces coated with a layer of oil. These liquid-infused surfaces have remarkable applications due to their ability to minimize contact line pinning. However, this property has mostly been exploited using liquid drops. We here study the early spreading behavior of a bubble once it has made contact with the liquid-infused surface. The final chapter is centered around the collapse of bubbles resting on the surface of an ultra viscous liquid. When a bubble on such a surface is ruptured, the bubble film collapses vertically downwards, leading scientists to believe that gravity is driving the collapse. Yet, interfacial forces are dominant in highly curved liquid surfaces and exceed gravitational forces. By turning the setup upside-down, we show that surface tension is indeed responsible for the collapse and the subsequent wrinkling instability that develops.

Non-wetting surfaces offer enhanced capabilities over bare metal substrates for condensation with or without phase change. This trait can be utilized to broaden strategies in combating water scarcity in water stressed areas. Slippery lubricant infused surfaces have the ability to shed water droplets with lower nucleation times, taking advantage of more of the limited amount of time available to collect dew and fog than traditional surfaces. However, existing studies focus on short durations with scant information available on the longer-term performance or durability of the materials in application environments. To address this knowledge gap, dew harvesting studies were conducted over a 96 hour period on a lubricant infused surface vis-à-vis regular surface of the same material. Three phases of performance are identified and discussed with regard to the water harvesting potential. The second part of the thesis addresses water condensation under conditions where freezing is a potential issue. Non-wetting surfaces have been shown to be a promising method of limiting the formation of ice from sessile droplets. This study explores the effect of surface roughness on the freeze time of sessile water droplets. Superhydrophobic and hydrophobic, lubricant infused, copper surfaces were created via electrodeposition and chemical etching in conjunction with chemical treatments to achieve non-wetting surfaces of varying surface textures. Freezing characteristics on the surfaces are studied experimentally and, for the first time, computationally, wherein the surface is described using a fractal surface topography. The effect of surface engineering on the freezing dynamics and comparison between the experimental and the computational studies are elucidated. / Master of Science / The use of durable, water repelling surfaces that are also thermally conductive provide an opportunity to help alleviate strain from a growing world crisis, water scarcity. Lubricant infused surfaces shed water from their surface by providing a slippery layer for the droplets to slide on, as opposed to bare metal which water tends to cling to. This behavior makes lubricant infused surfaces attractive as a water harvesting method. However, these surfaces degrade over time and must be maintained to perform at their maximum capability, collecting water for 40 minutes more than a bare surface. This thesis focuses on the performance of these surfaces over a 96-hour operating period to characterize the effect lubricant drainage has on the water collection behavior. Freezing water droplets, commonly referred to as icing, poses concerns for safety and operational ability in industries like renewable energy generation, where icing limits efficiency. Non-wetting surfaces have a unique ability to inherently slow down the phase change of a water droplet to ice due to the lower contact area of droplets resting on the surface. This thesis examines superhydrophobic and lubricant infused surfaces of varying degrees of roughness to explore the effect that the contact angle and different surface structures have on the freezing rate of water on the surface. The experimental results are compared to numerical simulations, which is useful in designing systems that would implement this passive icing mitigation technique.

Development of repellent surfaces which can supress bacteria adhesion, blood contamination and thrombosis, and non-specific adhesion on diagnostic devices has been a topic of intense research as these characteristics are in high demand. This thesis focused on design and development of omniphobic surfaces based on hierarchical structures and their application for preventing pathogenic contamination and biosensing. First, a flexible hierarchical heat-shrinkable wrap featuring micro and nanostructures, was developed with straightforward scalable methods which can be applied to existing surfaces. These surfaces reduced biofilm formation of World Health Organization-designated priority pathogens as well as minimized risk of spreading contamination from intermediate surfaces. This is due to the broad liquid repellency and the presence of reduced anchor points for bacterial adhesion on the hierarchical surfaces. Next, the developed surfaces were applied to minimize blood contamination and clot formation as well as facile integration of hydrophilic patterns. This led to droplet compartmentalization and was utilized for detection of Interleukin 6 in a rapid dip-based assay. Furthermore, in a review article the need for anti-viral or virus repellent surfaces and future perspectives were discussed as the global COVID-19 pandemic surged and attracted interest toward innovative technologies for suppressing the spread of pathogens. To address the pressing issue of non-specific adhesion in diagnostics devices, an omniphobic liquid infused electrochemical biosensor was developed. This was achieved by electroplating gold nanostructures on fluorosilanized gold electrodes. These electrodes demonstrated rapid and specific detection of Escherichia coli within an hour in complex biological liquids (blood, urine, etc.) without dilutions or amplification steps from clinical patient samples which are major bottle necks when rapid detection systems are sought for at the point of care. / Thesis / Doctor of Philosophy (PhD) / Repellent surfaces have a variety of applications in healthcare, for coating medical devices (e.g. indwelling implants, stethoscopes, and other external devices.), coating hospital surfaces for blood and pathogen repellency, and for developing anti-fouling diagnostic devices. Furthermore, they can be applied in the food sector for limiting contaminations, and in public areas on high-touch surfaces to eliminate the spread of infection. Therefore, there is a need for repellent surface which can be easily applied to surfaces with various form factors while having an easy fabrication method. Featuring hierarchical structures on a heat-shrinkable material, a repellent wrap was designed to be integrated on existing surfaces and repel pathogens and suppress the spread of infection as an intermediate surface. Similar concept was used for designing blood repellent surfaces which were patterned with hydrophilic regions for a rapid dip-based biosensing platform. Finally, surface textures on conductive materials with liquid infused repellent coatings were investigated for electrochemical biosensing in complex biological liquids.

Spontaneous expulsion of various forms and types of matter from their solid substrates has always been an integral part of interfacial physics problems. A thorough understanding of such interactions between a solid surface and different soft materials not only expands our theoretical knowledge, but also has applications in self-cleaning, omniphobic surfaces and phase-change heat transfer. Although there is a renewed interest in the design of robust functional surfaces which can passively remove highly viscous liquids or dew, or retard ice accretion or frost formation, the physics of several dewetting and/or deicing mechanisms are yet to be fully understood. Even though we know how jumping-droplet condensation offers significantly better heat transfer performance than regular dropwise condensation and can liberate foreign particles, fundamental questions on the effect of surface orientation on jumping-droplet condensation or how it helps in large-scale fungal disease epidemic in plants are still unanswered. Thus, we first try to fill the knowledge gap in jumping-droplet condensation by characterizing their orientation-dependence and their role in a large-scale pathogenic rust disease dissemination among wheat. Unfortunately, understanding of such dewetting mechanisms does not necessarily translates to prevention or removal of ice and frost on subzero surfaces. Use of superhydrophobic structures or hygroscopic materials to retard the growth of frost was found to be limiting. Therefore the search for an efficient, inexpensive, and environmentally favorable anti-icing or de-icing mechanism is still underway. Here we give a framework for making a novel de-icing construct by analyzing a peculiar jumping frost phenomena where frost particles spontaneously jump off the surface when a polar liquid is brought above. Lastly, we demonstrate a simple and cost-effective technique to design a slippery liquid-infused surface from low-density hydrocarbon-based polymers, which is able to effectively remove a wide variety of soft materials. The main all-encompassing theme of this dissertation is to enhance our understanding of several dewetting phenomena, which might enable better design and/or mitigation strategies to control the expulsion of various forms of matter from a wide variety of surfaces. / Doctor of Philosophy / A few years back, a laundry detergent company in India came up with a famous ad campaign; it showed kids coming home from school with dirt all over their clothes to face the wrath of their parents. Rather than casually disparaging their mischievousness, the ad would make us think with their tagline: "Agar daag (Lit. stain, Fig. mess) lagne se kuch achha hota hain, toh daag achhe hain na? (Fig. If something good comes out of a mess, is it a mess?)". While this presents to us an excellent philosophical conundrum, in reality, we always find ways to get rid of foreign materials from surfaces of everyday use. Using water or dirt-repellent coatings on our shoes/clothes/car windshields or in worst case, spending hours trying to clean frost off our cars is something we are all familiar with. Finding innovative ways to remove unwanted materials from surfaces is not limited to humans, but also exhibited by various natural organisms. The excellent water repellency of lotus leaves, antifogging abilities of mosquito eyes or cicada wings, and slipperiness of pitcher plants are just few examples of natural self-cleaning surfaces designed to keep foreign materials or dew droplets off the surface. Sometimes we take a leaf or two out of these natural designs to help our cause. Surfaces with extreme water repellency are called superhydrophobic (hydro: water, phobos: fear). For a long time, gravity was considered to be the only passive droplet removal mechanism on these surfaces. About ten years ago, researchers found out that when two or more small dew droplets come together on these surfaces, they jump off the surface. Compared to the gravity removal, much smaller droplets can be removed via this method resulting in better anti-fogging qualities and heat transfer performance on the surface. As the jumping droplet event itself is independent of gravity, it was long assumed that the performance of these surfaces would not be dependent on their orientation. These jumped droplets can also take off with contaminating particles by partially or fully engulfing them. A recent study has brilliantly showed how rust spores are liberated from the superhydrophobic wheat leaves via jumping dew droplets. This fundamentally new mode of pathogen transport is yet to be fully understood at the same scale as we know wind or rain-induced fungal spore transport. In this work, we try to fill the knowledge gap by answering questions such as whether the surfaces with the abilities of gravity-independent jumping-induced droplet removal ironically fail to gravity and how far can spore(s) travel engulfed in a jumped droplet. But it is not just water droplets (or particles collected by water droplets) on a surface that we want to get rid off. The solid phase of water, i.e., ice or frost, when formed on regular surfaces, is actually harder to remove. The common ice-preventing surfaces are generally unable to stop complete frost formation and forces us to use salt or other moisture attracting chemicals to remove ice from a surface, knowing very well what is the economic and environmental cost of these chemicals. Here, we have introduced a novel de-icing mechanism by holding only a drop of water over a sheet of frost. The simplicity of our experimental setup may remind you the home physics experiments we all did in our childhood. We finish our discussion by designing a slippery surface from regular polymer films used in food packaging. Although the idea behind these slippery surfaces has been around since 2011, polyethylene films have never been used to make such surfaces before. Here, we show through extensive characterization that by choosing a suitable lubricating oil and a polyethylene-based film, we can finally get all of our ketchup to slide out of their packets, without struggle. If the future design of superhydrophobic condensers, de-icing constructs, or slippery surfaces benefit from the work reported here, may be I can finally say with certainty, "Daag Achhe Hain (Dirt is good.)."

Nanocellulose is an interesting natural material thatis gaining interest in the field of materials science, particularly nanocomposites. Depending on the disintegration route, nanocellulose can be isolated either in the form of long and flexible fibres (nanofibrillated cellulose, NFC), or stiff, rod-like crystals (cellulose nanocrystals, CNC). Nanocellulose can be utilized in nanocomposites either as a reinforcement element or as a network matrix due to its ability to form a strong network. In this thesis, nanocellulose based materials are prepared by evaporation of a liquid medium. The key step in this processing route is a good dispersion of the nanoparticles in the selected matrix. Therefore the importance of surface modification in order to ensure favourable nanocellulose dispersion is clarified in avariety of materials systems. In Paper I, poly(methyl methacrylate) (PMMA) based fibres prepared by electrospinning were reinforced with nanofibrillated cellulose. Native NFC appeared to show a good compatibility with PMMA matrix in the electrospinning solution and resulting fibres. Furthermore, a new method for mechanical testing of mats with random fibre orientation as well as aligned fibres was developed. In Paper II, commingled nanopaper structures with carbon nanotubes (CNTs) were prepared. Several surfactants were used to disperse hydrophobic CNTs in water. A nonylphenol phosphate ester (NPPE) was found to work well for both dispersing CNTs in water and providing compatibility with NFC through electrostatic repulsion between the phosphate ester groups of the surfactant and the carboxylate groups of NFC. In Paper III, a new water based route for functionalization of cellulose nanocrystals was developed. In this approach, inspired by organo-modified layered silicates, quaternary ammonium salts were adsorbed. It was demonstrated that different functionalities (alkyl, phenyl, glycidylor diallyl) can be introduced onto the cellulose and the dispersibility in organic solvents was studied. Subsequently, in Paper IV, nanocomposites with poly(vinyl acetate) (PVAc)were prepared. The effect of modification on the degree of dispersion of the CNC within the matrix was studied as well as the strong effects on the properties of the resulting nanocomposites. In Paper V, taking advantage of the entangled NFC network and the possibility to tailor the pore size and surface chemistry, lubricant-infused slippery films and coatings based on NFC were prepared for the first time. / <p>QC 20131016</p>