Smart thermal management by which ultra-high heat fluxes (i.e., q''> 100 W/cm²) are dissipated efficiently, is increasingly desirable for many applications in aerospace, electronic packaging, metallurgy, as the existing cooling solutions are highly constrained. For example, the cooling strategy for aircraft must be executed in such a way that will operate independently of orientation while also screen out external heat loads coming from the neighboring electronic boxes and/or external sources. Therefore, it is crucial to develop heat transfer devices which could effectively dump heat away while additionally shield against external heat loads. Thermal diodes, by definition, accomplish this desirable unidirectional heat transfer functionality. Nonetheless, the existing thermal diodes are currently constrained by either a low diodicity (i.e., heat transfer ratio), gravitational dependence, a one-dimensional configuration, or poor durability. Further example for the necessity of smart thermal management would be in firefighting and nuclear reactor safety. Above a critical temperature referred to as the ``Leidenfrost temperature'', the highly effective nucleate boiling is completely replaced by insulating film boiling, causing a dramatic decrease in the essential cooling rate of water pool boiling and spray quenching. In chapter 2, after noting the mechanism and shortcomings of each existing solid-state and phase-change thermal diode, we develop a unique thermal diode, called bridging-droplet thermal diode, which operates independent of orientation, is planar and durable. Our diode is comprised of two opposing copper plates separated by an insulating gasket of micrometric thickness; one plate contains a superhydrophilic wick structure while the other is smooth and hydrophobic. In the forward mode of operation, water evaporates from the heated wicked plate and condenses on the opposing hydrophobic plate. The large contact angle of the dropwise condensate enables bridging across the gap to replenish the wicked evaporator, providing sustained phase-change heat transfer. Conversely, in the reverse mode the heat source is now on the hydrophobic plate, resulting in dryout and excellent thermal insulation across the gap. An orientation-independent heat transfer ratio (i.e. diodicity (η)) of approximately 85 was experimentally measured. In chapter 3, after highlighting that our experimental proof-of-concept discussed in chapter 2, was limited to only a narrow parameter space, we develop a comprehensive thermal circuit model for both the forward and reverse modes of operation to theoretically characterize the bridging-droplet thermal diode over a broad parameter space. Parameters that are varied include the gap height, input heat flux, effective thermal conductivity of the wetted wick structure, height of the wicking micropillars, wettability of the opposing smooth surface, and heat sink temperature. Our findings show that a vapor space height of Hᵥ≈ 250 μm, short and densely packed micropillars, a higher applied heat flux in the forward mode, and a hotter heat sink temperature result in optimal diodicities of η~ 100. In chapter 4, we discuss that the Leidenfrost effect has been a two-phase phenomenon thus far: either an evaporating liquid or a sublimating solid levitates on its vapor. Here, we demonstrate that an ice disk placed on a sufficiently hot surface exhibits a three-phase Leidenfrost effect, where both liquid and vapor films emanate from under the levitating ice. Curiously, the critical Leidenfrost temperature was over three times hotter for ice than for a water drop. As a result, the effective heat flux was an order of magnitude larger when quenching aluminum with ice rather than water over a wide temperature range of 150--550 °C. An analytical model reveals the mechanism for the delayed film boiling: the majority of the surface's heat is conducted across the levitating meltwater film due to its 100 °C temperature differential, leaving little heat for evaporation. In chapter 5, we note that nucleate boiling achieves dissipative heat fluxes as high as q''~ 100 W/cm² and is widely used for power plants, spray quenching metal alloys, desalination, and electronics cooling. However, above a Leidenfrost temperature of about 150 °C for water, an insulating vapor film massively degrades the heat flux by two orders of magnitude. Here, we demonstrate that robust nucleate boiling can be maintained even at temperatures as high as 400 °C by using ice particles in place of water droplets. Ice pellets are periodically released onto a superheated stage and compared to spray quenching at an equivalent mass flow rate. Ice quenching was twice as fast as spray quenching at low superheats, and at large superheats, only ice quenching is successful. Our results demonstrate that ice quenching can maintain groundbreaking heat fluxes of q''~ 100--1,000,W/cm² over a broad range of superheats, far superior than classical spray quenching. / Doctor of Philosophy / Smart thermal management by which enormous heat generated in avionics, electronic packaging, wildfire, etc are removed efficiently, is increasingly desirable as the current cooling solutions are highly constrained. For example, in the context of aircraft, equipment must be cooled down independent of aircraft orientation while also they are shielded from neighboring and/or external heat sources. In firefighting where the temperature of wildfire flames could get beyond 500 °C, dumping large volume of water from aircraft may not be adequate to quench the fire over a reasonable time frame as the liquid water loses its cooling effectiveness above a critical temperature. In chapter 2, after a brief review of existing cooling devices and their corresponding shortcomings commonly used in aircraft and electronic packaging, we develop a unique device for cooling of aircraft which operates independent of aircraft orientation, is durable over time, and can cool down surfaces irrespective of their dimensions. In chapter 3, after highlighting that our proof-of-concept of a new cooling device in chapter 2, was limited to only a finite number of experiments, we theoretically model the operating mechanism of our device to check for the criteria where our device works most efficient. In chapter 4, we discover that by placing an ice disk on a sufficiently hot surface, effective boiling where large amount of heat can be dumped away from the surface to the coolant, is extended to a very large surface temperature. To be specific, liquid water on smooth aluminum loses its cooling efficiency around 150 °C, while cooling the same surface with ice is still effective up to 550 °C. In chapter 5, we report that quenching with ice is twice as fast as quenching with liquid water at low surface temperatures (i.e., 150--300 °C), and at larger surface temperatures (i.e., beyond 300 °C), only ice quenching is successful. Comparing our ice quenching results against current cooling technologies, we note that ice quenching is superior.

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.)."

The defect structure, atomic structure, and energy of the interphase boundaries between an fcc matrix and a lath-shaped bcc precipitate in Ni-45 wt% Cr were investigated. The interfacial structure on the side facet of the precipitate consists of regular structural ledges and misfit dislocations. No regular defect structure can be found on the habit plane, or broad face, of the lath except for atomic-scale structural ledges. High resolution electron microscopy (HREM) observations show the (12¯1)_f habit plane is coherent and is a good matching interface. Based upon conventional transmission electron microscopy (TEM) observations, the orientation of the habit plane results from advancing growth ledges on the conjugate plane of the Kurdjumov-Sachs orientation relationship. Using embedded atom method (EAM) simulations, the interfacial energy of the (12¯1)_f habit plane is calculated and the simulated interphase structure is compared with the HREM observations. The simulated interface represents a major portion of the observed interface. The calculated interfacial energy of the (12¯1)_f habit plane is 210 mJ/m², lower than typical grain boundary energies indicating this habit plane is a low-energy interphase boundary. A non-Bain lattice correspondence is identified and employed to predict the (12¯1)_f habit plane successfully, although a Bain correspondence is more successful at predicting the elongation direction for the precipitate. Geometric matching is proposed to be responsible for determining the orientation of the precipitate habit plane and the growth direction. Lattice correspondence-based approaches such as the invariant line model and the phenomenological theory of martensitic crystallography can mimic aspects of geometric matching, but they do not accurately reflect the transformation mechanism during precipitation of bcc laths from an fcc parent. / Ph. D.

The measurement of the work of adhesion is of significant technical interest in a variety of applications, ranging from a basic understanding of material behavior to the practical aspects associated with making strong, durable adhesive bonds. The objective of this thesis is to investigate a novel technique using an elastica loop to measure the work of adhesion between solid materials. Considering the range and resolution of the measured parameters, a specially designed apparatus with a precise displacement control system, an analytical balance, an optical system, and a computer control and data acquisition interface is constructed. An elastica loop made of poly(dimethylsiloxane) [PDMS] is attached directly to a stepper motor in the apparatus. To perform the measurement, the loop is brought into contact with various substrates as controlled by the computer interface, and information including the contact patterns, contact lengths, and contact forces is obtained. Experimental results indicate that due to anticlastic bending, the contact first occurs at the edges of the loop, and then spreads across the width as the displacement continues to increase. The patterns observed show that the loop is eventually flattened in the contact region and the effect of anticlastic bending of the loop is reduced. Compared to the contact diameters observed in the classical JKR tests, the contact length obtained using this elastica loop technique is, in general, larger, which provides potential for applications of this technique in measuring interfacial energies between solid materials with high moduli. The contact procedure is also simulated to investigate the anticlastic bending effect using finite element analysis with ABAQUS. The numerical simulation is conducted using a special geometrically nonlinear, elastic, contact mechanics algorithm with appropriate displacement increments. Comparisons of the numerical simulation results, experimental data, and the analytical solution are made. / Master of Science

In this thesis the impact of inverted cones on a liquid surface is studied. It is known that with the right combination of velocity, geometry, and surface treatment, a cavity of air can be formed behind an impacting body and extended for a considerable distance. Other investigators have shown that the time and depth of the cone when this cavity collapses and seals follows a different power law for flat objects such as disks, then it does for slender objects such as cylinders. Intuitively it can be expected that a more slender body will have less drag and that the streamlined shape will not push the fluid out of it's way at impact to the same extent as a more blunt body, therefore forming a smaller cavity behind it. With a smaller initial cavity, the time and depth of it's eventual collapse can be expected to be less than that of a much more blunt object, such as a flat disk. To study this, a numerical model has been developed to simulate cones with the same base radius but different angles impacting on a liquid surface over a range of velocities, showing how the seal depth, time at cavity seal, and drag forces change. In order to ensure the numerical model is accurate, it is compared with experimental data including high speed video and measurements made of the force with time. It is expected that the results will fall inside the power law exponents reported by other authors for very blunt objects such as disks on one end of the spectrum, and long slender cylinders on the other. Furthermore, we expect that the drag force exerted on the cones will become lower as the L/D of the cone is increased. / Master of Science

Chloride ion induced corrosion of reinforcing steel in concrete bridge decks has become a major problem in the United States. Latex modified concrete (LMC), low slump dense concrete (LSDC) and hot-mix asphalt membranes (HMAM) overlays are currently some of the most used rehabilitation methods. Epoxy coated reinforcing steel (ECR) was developed and promoted as a long term corrosion protection method by the Federal Highway Administration (FHWA). However, recent evidence has suggested that ECR will not provide adequate long term corrosion protection. The Reynolds Metals Company has developed an aluminum bridge deck system as a proposed alternative to conventional reinforced steel bridge deck systems. The deck consists of a polymer concrete overlay and an aluminum substrate. The purpose of this investigation is to evaluate the bond durability between the overlay and the aluminum substrate after conditioning specimens in various temperature and humidity conditions. The average critical strain energy release rate, Gcr, for each specimen was measured using a modified mixed mode flexure (MMF) test. In this investigation the strain energy release rate is a measure of the fracture toughness of the interface between the polymer concrete overlay and the aluminum substrate. The different environmental conditionings all had a significant effect on the bond durability. Specimens conditioned at 30 degrees C [86 degrees F], 45 degrees C [113 degrees F] and 60 degrees C [140 degrees F] at 98 % relative humidity all showed a decrease in interfacial bond strength after conditioning. A decrease in the interfacial bond strength was also observed for the specimens conditioned in freezing and thawing cycles as well as specimens conditioned in a salt water soak. Of the exposure conditions used in this investigation, the only one that showed an increase in the bond strength was drying the specimens continuously in an oven at 60 degrees C [140 degrees F]. / Master of Science

No / Widefield surface plasmon resonance (WSPR) microscopy provides high resolution imaging of interfacial interactions. We report the application of the WSPR imaging system in the study of the interaction between keratinocytes and liquid crystals (LC). Imaging of fixed keratinocytes cultured on gold coated surface plasmon substrates functionalized with a thin film of liquid crystals was performed in air using a 1.45 NA objective based system. Focal adhesion of the cells adhered to glass and LC were further studied using immunofluorescence staining of the vinculin. The imaging system was also simulated with 2 × 2 scattering matrix to investigate the optical reflection of the resonant plasmonic wave via the glass/gold/cell and glass/gold/LC/cell layers. WSPR imaging indicated that keratinocytes are less spread and formed distinct topography of cell–liquid crystal couplings when cultured on liquid crystal coated substrates. The simulation indicates that glass/LC shifted the surface plasmon excitation angle to 75.39° as compared to glass/air interface at 44°. The WSPR microcopy reveals that the cells remodelled their topography of adhesion at different interfaces.

The interfacial fracture performance of dicyandiamide cured epoxy/steel adhesive systems was thoroughly investigated. Fracture mechanics based testing was utilized to study several variables which were believed to influence the epoxy/steel interphase region, specifically the elasomeric toughener concentration, the dicyandiamide concentration, and the cure temperature. Bulk mechanical measurements were conducted to provide background information for comparison with the fracture data, and surface analyses were carried out on the neat adhesives and failed fracture specimens to provide insight into the locus and causes of failure. The addition of toughener drastically impacted the morphological, bulk mechanical, and adhesive properties in these latent cure systems. Modulus values decreased and bulk fracture toughness values increased with increasing toughener content. Static double cantilever beam (DCB), fatigue DCB, and notched coating adhesion (NCA) interfacial fracture performances all increased. X-ray photoelectron spectroscopy (XPS) and tunneling electron microscopy (TEM) analyses of the failed specimens revealed that chemical changes were more prominent at the epoxy/steel interphase than in the bulk of the materials. Morphological variations were also apparent with toughener level variations, but for a single formulation no differences between the bulk and intephase morphologies were seen. Evaluations were conducted on a series of elastomer modified model epoxy formulations cured with varying amounts of dicyandiamide. The modulus and bulk fracture toughness values were shown to be independent of dicyandiamide concentration, whereas the adhesive performance was greatly influenced. For increases in the concentration of dicyandiamide, single lap shear (SLS) failure strength values increased while quasi-static DCB and NCA test performances decreased. Fatigue DCB results showed improved adhesive performance at both high and low levels of dicyandiamide content. The results of the failure surface evaluations suggest that dicyandiamide variations produce significant chemical changes only in the epoxy/steel interphase region, and not in the bulk. Analyses were conducted on all of the above systems using two additional cure temperatures. The purpose of this work was to alter the dicyandiamide solubility, and possibly the dicy/epoxy reaction mechanisms, and to determine what influence these changes had on the interfacial fracture performance. In general it was found that performance increased as the cure temperature was increased. / Ph. D.

The target of the ‘Green Overlays’ research was a cost effective, minimal disruption, sustainable and environmentally friendly alternative to the wholesale demolition, removal and complete reconstruction of the existing structural concrete pavement. The important problem of flexural resistance for strengthening concrete pavements with structural overlays has been scrutinised. A new mix design method for steel fibre reinforced, roller compacted, polymer modified, bonded concrete overlay has been proposed. The mixes developed were characterized of high flexural strength and high bond strength with the old concrete substrate. ‘Placeability’ and ‘compactability’ of the mix were two dominant issues during laboratory investigation. An innovative approach for establishing the relationship between Stress and Crack Face Opening Displacement for steel fibre reinforced concrete beams under flexure was developed. In addition, a new and simple method for calculating the interfacial Strain Energy Release Rate of both, a two-dimensional specimen and a three-dimensional model of the overlay pavement system were developed. This method can be readily and easily used by practicing engineers. Finally, a new test specimen and its loading configuration for measuring interfacial fracture toughness for concrete overlay pavements were established. The interfacial fracture toughness of a composite concrete beam, consisted of steel fibre-reinforced roller compacted polymer modified concrete bonded on conventional concrete and undergoing flexure, was assessed. In summary, this thesis presents four key findings: A new mix design method for steel fibre-reinforced roller compacted polymer modified concrete bonded on conventional concrete. A new method for establishing the fibre bridging law by an inverse analysis approach. A new, simplified method for calculating strain energy release rate at the interface of a composite beam. A new, innovative technique for calculating strain energy release rate at the interface of an overlaid pavement. The thesis contains a plethora of graphs, data-tables, examples and formulae, suitable for future researchers.

L’objectif de cette étude a été de formuler et caractériser des émulsions simples huile/eau d’intérêt pharmaceutique stabilisées par de la β-lactoglobuline (β-lg), de la gomme arabique (GA), de la gomme xanthane (GX) et des mélanges β-lg:GA et β-lg:GX. Les concentrations massiques totales des dispersions de biopolymères étaient de 1 % et ont été augmentées à 2,5 % si les émulsions formulées n’étaient pas stables. Le mélange β-lg:GA a été réalisé à pH 4,2 afin de permettre la formation de complexes par interactions électrostatiques attractives entre la β-lg et la GA. Deux ratios β-lg:GA ont été étudiés : 2:1 et 1:2. Enfin, le mélange β-lg:GX a été effectué à pH 7, où les deux biopolymères étant chargés négativement ne se complexent pas et à un ratio de 1:1. Une étude de stabilité des émulsions a été menée sur 6 mois. Les stabilités obtenues ont pu être classées par ordre croissant : GA 2,5 % < β-lg:GA 2,5 % < β-lg 2,5 % < GX 1 % = β-lg:GX 1 %. Plusieurs mécanismes de stabilisation ont été mis en évidence grâce à l’étude des propriétés interfaciales des biopolymères, à l’étude des propriétés rhéologiques des émulsions et à des observations au microscope confocal à balayage laser des émulsions après marquage des biopolymères à la fluorescence. La β-lg et la GA sont toutes deux capables de s’adsorber à l’interface des globules huileux alors que la GX augmente la viscosité de la phase continue. L’association β-lg:GA conduit à la formation d’une double couche interfaciale stabilisante. Enfin, l’association β-lg:GX combine les mécanismes de stabilisation de la protéine, par adsorption interfaciale et de la gomme, par augmentation de la viscosité de la phase continue. / The main objective of this study was to formulate and characterize oil-in-water simple emulsions of pharmaceutical interest stabilized by β-lactoglobulin (β-lg), gum arabic (GA), xanthan gum (XG), and mixtures of β-lg:GA and β-lg:XG. The total biopolymer final concentration in the dispersions was 1 (w/w) % and could be raised to 2.5 (w/w) % if the formulated emulsions were not stable. β-lg:GA mixing was performed at pH 4.2 to allow attractive electrostatic interactions between the two biopolymers and thus the formation of complexes. Two protein:polysaccharide ratios were investigated: 2:1 and 1:2. Conversely, β8lg:XG mixing was performed at pH 7, where both biopolymers are negatively charged, in order to avoid the complex formation, and with a 1:1 ratio. A stability study was conducted for emulsions over a 6-month period. The obtained stabilities could be classified increasingly: GA 2.5 % < β-lg:GA 2.5 % < β-lg 2.5 % < XG 1 % = β-lg:XG 1 %. Several stabilization mechanisms were evidenced by the study of the biopolymer interfacial properties, the study of emulsion rheology and by confocal laser scanning microscopy observations with labeled fluorescent biopolymers. β-lg and GA were both able to adsorb at the interface of oil globule. XG enhanced the continuous phase viscosity. β-lg:GA mixing led to the formation of a stabilizing interfacial double layer. Finally, β-lg:XG association combined the stabilization mechanisms of both biopolymers, respectively: interfacial adsorption and enhancement of the continuous phase viscosity.