Στην παρούσα διατριβή, ερευνάται αν οι διακυμάνσεις της τριχοειδούς πίεσης είναι δυνατό να παράσχουν ποσοτική πληροφορία που αφορά τη χωρική κατανομή της διαβροχής σε πορώδη μέσα κλασματικής διαβροχής. Για το σκοπό αυτό πραγματοποιήθηκαν πειράματα εκτόπισης της ελαϊκής φάσης από υδατική υπό σταθερή παροχή σε πορώδη μέσα κλασματικής διαβροχής. Τα πορώδη μέσα κλασματικής διαβροχής κατασκευάστηκαν με τυχαία ανάμιξη γυάλινων και πλαστικών (PTFE) σφαιρών, απαράλλαχτης διαμέτρου, έτσι ώστε η γεωμετρία των πόρων να διατηρηθεί αναλλοίωτη. Η χωρική κατανομή των διαφορετικών ειδών σφαιρών διέφερε ακόμη και όταν τα σχετικά τους κλάσματα ήταν ίδια. Κατά τη διάρκεια των πειραμάτων λαμβάνονταν μετρήσεις της μεταβατικής απόκρισης της τριχοειδούς πίεσης και στιγμιότυπα της εκτόπισης ανά τακτά χρονικά διαστήματα. Αρχικά πραγματοποιήθηκαν πειράματα εκτόπισης σε πορώδη μέσα που ήταν ενδιάμεσα υδατοδιαβρεκτά και ισχυρά ελαιοδιαβρεκτά. Τα ληφθέντα σήματα τριχοειδούς πίεσης, αναλύθηκαν με τη μέθοδο των κυματιδίων (wavelet) και συσχετίσθηκαν με τα γεγονότα ροής που ελάμβαναν χώρα. Η διαβροχή των περιοχών των πορωδών μέσων που εισδύονταν από υδατική φάση περιγράφηκε μέσω ενός εμπειρικού δείκτη διαβροχής ο οποίος συσχετίστηκε με τα φάσματα λεπτομέρειας που προέκυψαν από την ανάλυση των σημάτων. Στην περίπτωση ομοιόμορφης και ενδιάμεσης υδατοδιαβροχής ευνοούνται γεγονότα ροής που συνοδεύονται από σημαντικές διακυμάνσεις της τριχοειδούς πίεσης ώστε να καθίσταται δύσκολη η παραπάνω συσχέτιση. Για το λόγο αυτό πραγματοποιήθηκαν πειράματα εκτόπισης με χρήση ενός δεύτερου ζεύγους ρευστών. Τα πορώδη μέσα κλασματικής διαβροχής ως προς το δεύτερο ζεύγος ρευστών ήταν υδατοδιαβρεκτά και ισχυρά ελαιοδιαβρεκτά. Στην περίπτωση του δεύτερου ζεύγους ρευστών, τα σήματα τριχοειδούς πίεσης χαρακτηρίζονταν από αργές και μικρές σε ύψος διακυμάνσεις. Αυτή η διαφορετικότητα επέβαλλε τη βελτίωση της μεθόδου ανάλυσης των σημάτων ώστε να μπορεί να εφαρμοστεί σε όλα τα σήματα που ελήφθησαν στα πειράματα εκτόπισης της παρούσας εργασίας. Υιοθετήθηκαν πλέον δύο εμπειρικοί δείκτες διαβροχής: ο πρώτος δείκτης, Λ, δηλώνει τη διαβροχή της ενεργούς διεπιφάνειας και ο δεύτερος δηλώνει τη διαβροχή της επιφάνειας του πορώδους μέσου που γεμίζει με υδατική φάση όταν κινηθεί η προαναφερθείσα διεπιφάνεια. Οι δύο δείκτες διαβροχής συσχετίστηκαν με την «ενέργεια» των σημάτων, τη «συχνότητα» των φασμάτων λεπτομερειών του βέλτιστου επιπέδου ανάλυσης των σημάτων και τις χρονομέσες τιμές τριχοειδούς πίεσης. / A transparent porous medium of controlled fractional wettability is fabricated by mixing water-wet glass microspheres with strongly oil-wet polytetrafluouroethylene microspheres and packing them between two transparent glass plates. The displacement experiments performed for two pairs of fluids: a) silicon oil and water and b) paraffin oil and water. The growth pattern is video recorded and the transient response of the pressure drop across the pore network is measured for various fractions of oil-wet particles. The measured global capillary pressure fluctuates as the result of the variation of the equilibrium curvature of menisci between local maxima and local minima. By using wavelet transform on the capillary pressure signal, the best level detail spectrum arises and its peaks indict the parts of the original signal with the most important fluctuations, each of those is analyzed again. The best level detail coefficients give the “energy” of the analyzed part of the capillary pressure signal while the number of the most important fluctuations of the best level detail spectrum to the time interval they took place gives the “frequency” of the best level detail spectrum. The time averaged capillary pressure, the “energy” and the “frequency” are associated with the frontal wettability of the interface separating the two fluids before the invasion step and one number which denotes the regional wettability of the invaded area.

The research topic of liquid drop interaction with solid surfaces is being actively pursued to gain in-depth understanding of several practical cases such as the impingement of fuel spray droplets on surfaces like combustion chamber walls and piston top of an I.C. engine, heat transfer via spray impingement, ink-jet printing, etc. In most of the cases, the physical and flow properties of the liquid drop/spray may be fixed whereas it may be possible to tune the physical and chemical properties of the solid surface thereby enabling to control the interaction process. The present work belongs to the study of liquid drop-solid surface interaction process with special focus on the physical characteristics of solid surface. The thesis reports an experimental study of the dynamics of millimetric water drops impacted onto the junction of dual-textured substrates made of stainless steel. The dual-textured substrates consisted of hydrophobic (textured) and hydrophilic (smooth) portions. The entire textured portion comprised of parallel groove-like structures separated by solid posts/pillars. Two dual-textured substrates, which differ only in the geometry of their textured portions, were employed. Surface topography features of the dual-textured substrates were characterized using scanning electron microscopy (SEM) and optical surface profilometer. The wetting behavior of the textured and smooth portions of the substrates, quantified in terms of the equilibrium, advancing, and receding contact angles adopted by a water drop on the surface portions, was characterized experimentally through the methods of sessile drop formation, captive needle volume addition, and drop evaporation under ambient conditions. Free-falling water drops were impacted from a height onto the junction between the hydrophobic (textured) and hydrophilic (smooth) portions of the dual-textured substrates. A set of twelve different impact experiments were conducted on each of the target substrates with drop impact velocity (Uo) ranging from 0.37 to 1.50 m/sec. The dynamics of drop impact were captured using a high speed camera with frame rate ranging from 3000 to 10000 frames per second. From the captured frames, the temporal variations of the impacting drop parameters were measured using a MATLAB-assisted program. A systematic analysis of experimental data revealed the existence of four distinct regimes of drop dynamics on the dual-textured substrate: (a) early inertia driven drop spreading, (b) primary drop receding, (c) secondary spreading on the hydrophilic portion, and (d) final equilibrium regimes. It is shown that the drop impact dynamics during the early inertia driven impact regime remains unaffected by the dual-texture feature of the substrate. A larger retraction speed of impacting drop liquid observed on the hydrophobic portion of the substrate makes the drop liquid on the higher wettability/hydrophilic portion to advance further (secondary drop spreading). The net horizontal drop velocity towards the hydrophilic portion of the dual-textured substrate decreases with increasing drop impact velocity. The available experimental results suggest that the movement of bulk drop liquid away from the impact point during drop impact on the dual-textured substrate is larger for the impact of low inertia drops. A semi-empirical model, based on the balance of the wettability gradient, contact angle hysteresis, and viscous forces acting on impacted drop liquid on the substrate, is formulated to predict the movement of bulk drop liquid away from the impact point (ξ). A satisfactory comparison between the model predictions and the experimental measurements is reported for the variation of ξ with Uo.

Water management is a serious issue that affects the performance and durability of PEM fuel cells. It is known, from previous experimental investigations, that surface wettability has influence on water behaviour and fuel cell performance. This finding has lead researchers to develop numerical tools for further investigation of the liquid water behaviour in gas channels. The Volume-of-Fluid (VOF) method has been used in a wide range of studies for its advantage of showing the multi-phase interface in a Computational Fluid Dynamics (CFD) simulation to understand liquid water behaviour in gas channels. In this thesis, numerical study has been carried out to examine the behaviour of liquid water in gas channels. The dynamic movement of the liquid water in the channel and the associated pressure drop, water saturation and water coverage of the GDL have been investigated. Firstly, flow diffusion into the GDL was examined to determine its effect on liquid droplet behaviour in a small section of a gas channel. Furthermore, the effects of the percentage of flow diffusion, GDL wettability, pore size, and water inlet velocity were investigated. Fluid diffusion into GDL found to have insignificant impact on liquid water behaviour so further investigations has been carried with a solid GDL surface. Secondly, gas channel geometry effect on liquid water behaviour was studied. Square, semicircle, triangle, trapezoid with a long base and trapezoid with a short base were compared to find suitable cross section geometry to carry wall wettability investigations. Among the examined geometries, the square cross section showed reasonable results for both scenarios of geometry design, fixed Reynolds number and fixed GDL interface. The effect of wall wettability was assessed by comparing nine different wall/GDL wettability combinations for straight and bend channels. Wall wettability found to have an impact on liquid water behaviour but not as much as GDL wettability. It affects liquid water saturation in the channel by a great deal by accumulating water in the channel edges affecting water behaviour. This was also proven in the last test case of a long channel where water accumulation was investigated by running the calculation until the percentage of water saturation is stabilized. It is also concluded that changing wall wettability from hydrophobic to hydrophilic doubles the percentage of channel occupied by liquid water and increases the time to reach steady state.

Résumé: Le développement de l’industrie des polymères fourni de plus en plus de choix pour la formulation de matériaux pour les couvre-planchers. Les caoutchoucs, le PVC et le linoleum sont les polymères habituellement utilisés dans l’industrie des couvre-planchers. Ce projet répond à un problème de facilité de nettoyage des couvre-planchers de caoutchouc qui sont reconnus pour être mous, collants et ayant une surface rugueuse. L’INTRODUCTION couvrira l’état actuel de la recherche sur les couvre-planchers, surtout en regard au problème de la «nettoyabilité». La théorie pertinente et les informations générales sur les polymères, les composites polymériques et la science des surfaces seront introduites au CHAPITRE 1. Ensuite, le CHAPITRE 2 couvrira la méthode utilisée pour déterminer la nettoyabilité, l’évaluation des résultats ainsi que l’équipement utilise. Le CHAPITRE 3, discutera des premières expériences sur l’effet de la mouillabilité, la rugosité et la dureté sur la facilité de nettoyage des polymères purs. Plusieurs polymères ayant des surfaces plus ou moins hydrophobes seront investigués afin d’observer leur effet sur la nettoyabilité. L’effet de la rugosité sur la nettoyabilité sera investigué en imprimant une rugosité définie lors du moulage des échantillons; l’influence de la dureté sera également étudiée. Ensuite, un modèle de salissage/nettoyage sera établi à partir de nos résultats et observations afin de rationaliser les facteurs, ou « règles », qui détrminent la facilité de nettoyage des surfaces. Finalement, la réticulation au peroxyde sera étudiée comme une méthode de modification des polymères dans le but d’améliorer leur nettoyabilité; un mécanisme découlant des résultats de ces études sera présenté. Le CHAPITRE 4 étendra cette recherche aux mélanges de polymères; ces derniers servent habituellement à optimiser la performance des polymères purs. Dans ce chapitre, les mêmes tests discutés dans le CHAPITRE 3 seront utilisés pour vérifier le modèle de nettoyabilité établi ci-haut. De plus, l’influence de la non-miscibilité des mélanges de polymères sera discutée du point de vue de la thermodynamique (DSC) et de la morphologie (MEB). L’utilisation de la réticulation par peroxyde sera étudié dans les mélanges EPDM/ (E-ran-MAA(Zn)-ran-BuMA) afin d’améliorer la compatibilité de ces polymères. Les effets du dosage en agent de réticulation et du temps de cuisson seront également examinés. Finalement, un compatibilisant pré-réticulé a été développé pour les mélanges ternaires EPDM/ (E-ran-MAA(Zn)-ran-BuMA)/ HSR; son effet sur la nettoyabilité et sur la morphologie du mélange sera exposé. / Abstract: The development of industrial polymers provides more choices to the design of flooring materials. Rubbers, PVC and linoeleum are the most used polymers in the flooring industry. This project stems from the problem of cleanability (ease of cleaning) of the surface of rubber tile flooring which is known as a soft, sticky and rough surface. In the introduction, the current situation of research on the polymer flooring industry, especially the study on the cleaning problem will be introduced. The relevant theory and general information on polymers, polymer composites and surface science will be introduced in CHAPTER 1. In CHAPTER 2 different approaches, protocols and equipment to evaluate cleanability will be presented. The initial experiments and results (CHAPTER 3) will involve various fundamental concepts on surface wettability, roughness and hardness, as these properties can all influence the surface soiling and cleanability. In single-polymer systems, dozens of polymer materials with a hydrophobic or hydrophilic surface were investigated to observe their soiling and cleaning properties. The effect of roughness was also studied by surface printing method which is used to control the surface topography. Likewise, the influence of surface hardness on cleanability was also investigated with different polymer materials. From the above results and observations, a surface soiling/cleaning model is proposed in attempt to simplify the ― rules ‖ which determine the surface cleanability. Finally, peroxide crosslinking was investigated as a matrix modification method to improve the surface cleanability. The second part of the experiments and results (CHAPTER 4) extends to investigations of polymer blends, in attempt to optimize the performance of single-polymer materials. In this chapter, the surface cleaning model and its relevant rules are examined by the wettability, roughness and hardness tests discussed in CHAPTER 3. The influence of immiscibility on cleaning performance will be discussed in polymer blends from the point of view of thermodynamics (DSC) and morphology (SEM). In order to improve the compatibility in polymer blends, peroxide crosslinking was performed in EPDM/ (E-ran-MAA(Zn)-ran-BuMA) blends. The dosage of curing (cross-linking) agent and curing time were investigated to observe the influence of these experimental conditions on cleanability. Finally, a blend compatibilizer was designed to improve the compatibility of the EPDM/ (E-ran-MAA(Zn)-ran-BuMA)/HSR blends.The compatibilizer prepared by partial pre-crosslinking of EPDM (Nordel) and E-ran-MAA(Zn)-ran-BuMA (Surlyn) was incorpo rated in polymer composites and its influence on cleanability was studied and explained on the basis of changes in morphology of the blend polymer matrix.

No description available.

The control of cell adhesion to synthetic polymers is a key factor in tissue engineering, resting on the ability to direct specific cell types to adhere and proliferate in order to stimulate tissue reconstruction. But often the surface properties are compromised for the sake of the bulk properties, leading to surfaces that do not support sufficiently the level of bioactivity required and accordingly the polymeric biomaterial will fail clinically. Laser treatment offers a unique means of enhancing the osteoblast cell response of the surface of a polymeric biomaterial, whilst keeping the already sufficient bulk properties intact. To this end, infra-red (IR) and ultraviolet (UV) lasers have been employed to modify the wettability characteristics of nylon 6,6, as wetting is often the primary factor dictating the adhesion and bonding potential of materials, as a route to enhancing the surface in terms of osteoblast cell response. What is more, modifying wettability characteristics in this way is a highly attractive means of estimating the biofunctionality of a polymer. IR (CO2) and UV (F2 and KrF excimer) lasers were employed to carry out two different processes: laser whole area irradiative processing and laser-induced patterning. With both CO2 and the excimer lasers changes in the wettability characteristics could be effected with subsequent enhancement of osteoblast cell response. This was also the case with both laser-induced patterning and laser whole area irradiative processing. Essentially, an approach has been established whereby the osteoblast cell response on the surfaces of laser treated nylon 6,6 can be predicted through the laser-induced wettability characteristics modification, particularly for the laser whole area irradiative processed nylon 6,6. This ultimately allows one to determine the osteoblast cell response of the laser surface treated nylon 6,6 surfaces directly from the laser operating parameters. In concurrence with established wetting theory the laser whole area irradiative processing of the nylon 6,6 surfaces caused increased surface roughness, increased surface oxygen content, increased polar component, γP , and increased total surface energy, γT ; thereby generating surfaces displaying reduced contact angle, θ, making the nylon 6,6 surfaces more hydrophilic. The laser-induced patterned samples differed from current theory insofar as the nylon 6,6 surfaces became less hydrophilic due to an increase in θ despite an increase in surface roughness, an increase in surface oxygen content, an increase in γP and an increase in γT . This phenomena can be explained by the transition in wetting regimes from a Wenzel regime to a mixed-state wetting regime. Nevertheless, collation of the wettability characteristics results revealed that θ was a strong correlative decreasing function of both γP and γT , indicating that surface energy played a large role in determining the wetting nature of the nylon 6,6. It was found that for all laser whole area irradiative processed nylon 6,6 surfaces the osteoblast cell response was an increasing correlative and therefore predictive function of θ and was a decreasing function of γP . To an extent, the surface oxygen content and surface roughness could be used indirectly to foretell the osteoblast cell response of the nylon 6,6 surfaces. This is on account of the CO2 and KrF excimer laser whole area irradiative processing bringing about increased surface toxicity, which above a certain level hindered the osteoblast cell response. For the laser-induced patterned nylon 6,6 samples there did not appear to be any particular correlative trend between the modified surface parameters and osteoblast cell response. This can be accounted for by the transition in wetting regimes. Another important factor is that cell morphologies were modulated over all samples which suggests that varying surface parameters on account of laser surface treatment gave rise to variations in cell signaling. It was determined that θ, γP and γT all had very strong correlative relationships with the cytotoxicity. The cytotoxicity reduced upon an increase in θ until a minimum constant was achieved, whereas the cytotoxicity remained constant at low γP and γT until a point at which the cytotoxicity began to increase. These results are noteworthy as they allow one to deduce that, with constant cytotoxicity levels, the osteoblast cell response appeared to be modulated by the wettability characteristics. But once the cytotoxicity increased, the toxicity began to dominate and so negated the identified positive wettability characteristic correlations with osteoblast cell response. Practically, the surface roughness and surface oxygen content could be implemented indirectly to estimate the cytotoxicity. Increase in cytotoxicity was the result of the laser processing with higher fluences generating excessive melting. As a result of this, it is possible to deduce that there was a maximum threshold fluence, beyond which the toxicity of the nylon 6,6 began to dominate, giving rise to a less enhanced osteoblast cell response. On account of the correlative trends which have been identified between the laser surface treatment, wettability characteristics and osteoblast cell response of nylon 6,6 it is likely for one to have the ability to estimate the osteoblast cell response in vitro. This is significant as it indicates that laser surface modification of polymeric materials could have tremendous potential for application within the field of regenerative medicine.

The time-dependent wettability of nickel nanorod arrays was studied by measuring their water contact angles as a function of "aging" time in air. The nickel nanorod arrays were deposited on silicon substrates by DC magnetron sputtering using an oblique angle of 85° with respect to the substrate normal. By changing the deposition time from 10 to 90 min., the diameter, height, and separation of the nanorods were varied. The water contact angles of each sample were then periodically measured from a minimum aging time of 30 min. after deposition and exposure to air, up to a maximum aging time of three months. The initial water contact angles for all samples were approximately equal to 8o, indicating that the nickel nanorod arrays were initially superhydrophilic. As the samples aged in air, however, they all showed increasing contact angles as a function of time that were nonlinear with different rates. The results can be grouped into two categories: thinner samples with shorter deposition times (10 to 55 min) demonstrated faster rates of increase in contact angle, and thicker samples with longer deposition times (60 and 90 min.) showed slower rates. The increase in contact angle with time indicates that the Ni nanorods become more hydrophobic with aging time in air. Surface chemical analysis demonstrates that this increase in hydrophobicity may be due to oxidization and hydrocarbon contamination, which depend on the nanorod morphology. X-ray photoelectron spectroscopy results indicate that thinner samples (10-55 min. deposition time) have more adsorbed carbon as compared to thicker samples (60 and 90 min.). It appears that the reactivity of the Ni nanorods with air ambient is enhanced for shorter, smaller-diameter nanorods.

In this thesis, both the wettability and the agglomeration characteristics of non-metallic inclusions in liquid iron/steel were studied by using both experimental results and thermodynamic considerations. The mechanisms of the wettability of different types of inclusions were discussed. Also, the agglomeration behaviors of the inclusions were analyzed. Firstly, the wettability of different types of inclusions (including Al2O3, MgO, Ti2O3, TiO2 and TiN) in contact with the liquid iron/steel was studied. For the TiNcase, there is no reaction formation at the interface between TiN and pureiron/steel. In the caseo f pure Fe, the oxygen increase is the main factor for a contact angle decrease. As for the steel case, a sharp decrease of the contact angle is due to the effects of both an increased oxygen content in the liquid steel and a formation of a Ti(N,C,O) phase at the interface. For the Al2O3 and MgO cases, the formation of a FeAl2O4 and a MgO-FeO reaction layer at the interface, respectively, lead to a contact angle decrease. In the case of the Ti2O3/pure Fe case, the reaction at the interface cannot be identified. For the Ti2O3/steel case, the formation of an Al2TiO5 reaction layer is the main reason for a steep decrease of the contact angle. In the TiO2 case, the melting region appears at the temperature below the melting point of pure iron. This is due to the strong formation of a solid solution TiOx-FeO. The main source of the oxygen for the solid solution formationis due to a TiO2 substrate decomposition and a low partial pressure of oxygen in the chamber. Regarding to the non-metallic particle additions (TiO2 and TiN) into the molten steel, the steel composition should be controlled to have a small Al content (&lt;0.005mass%) and a high Ti content (&gt;0.035mass%), so as togeta high number of Ti-rich oxide inclusions with a small size. This conclusionis supported from the view point of the van der Waals force, liquid-capillary force and wettability. Regarding the Ti/Al complex deoxidation in the melt, the “mainly occupied clustered inclusions” with spherical shape is due to a TiOx-FeO liquid inclusion precipitation after an addition of Ti as a pre-deoxidizer. The much lower cluster number in the Ti/Al case than that in the Al case is mainly due to a coagulation of single TiOx-FeO liquid inclusions. Also, the cluster formation in a complex Ti/Al deoxidation is started after an Al addition rather than after a Ti addition. Regarding the Al2O3 cluster formation in deoxidation, the cavity bridge forceis larger than the van der Waals force. However, the difference between them is smaller than 7 times. In the reoxidation process, the influence of the cavity bridge force due to the wettability decreased, and became similar to that of the liquid-capillary force. / <p>QC 20160301</p>

Orientador: Elaine Maria Cardoso / Resumo: O avanço de novas tecnologias, associado à minimização dos custos de fabricação e instala-ção, constitui um grande desafio para a área de refrigeração, uma vez que a geração de calor tem aumentado gradativamente nos últimos anos. Assim, a busca de novos fluidos com pro-priedades térmicas superiores aos comumente usados tornou-se indispensável para melhorar a eficiência energética. Nas últimas décadas os nanofluidos - dispersões de partículas de escala nanométrica (1 a 100nm) em um fluido-base - têm atraído especial interesse não somente da comunidade acadêmica, mas também da indústria em áreas como: a microeletrônica, microflu-ídica, transporte, manufatura, assistência médica, entre outras. O melhor desempenho térmico e a vasta gama de aplicações fazem dos nanofluidos potenciais substitutos dos refrigerantes utilizados em diversos segmentos da engenharia. Dentro desse contexto, o presente trabalho teve como objetivos: o estudo teórico e experimental da influência das propriedades termofísi-cas e concentração de nanofluidos, bem como, das características geométricas da superfície aquecedora sobre o ângulo de contato e a molhabilidade. Também, atenção foi dada à prepa-ração e caracterização dos nanofluidos (Al2O3-água e Fe2O3-água), por meio da análise expe-rimental da condutividade térmica e da viscosidade dinâmica para diferentes concentrações; uma bancada experimental, para aquisição de imagens de gota séssil, foi construída a fim de viabilizar as análises de ângulo de conta... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The advance of new technologies, associated to the minimization of manufacturing and installation costs, presents a great challenge for the refrigeration area, since the heat generation has increased in recent years. Thus, the search for new fluids with thermal properties higher than those commonly used has become indispensable to improve energy efficiency. In recent decades, nanofluids-dispersions of nanometer-scale particles (1 to 100 nm) in a base fluid - have attracted special interest not only from the academic community but also from industry in areas such as microelectronics, microfluidics, transport, manufacturing, medical assistance, among others. In this context, the present work had the following goals: the theoretical and experimental study of the influence of thermophysical properties and nanofluid concentration, as well as the geometric characteristics of the heating surface on the contact angle and wetta-bility. Attention was also given to the preparation and characterization of nanofluids (Al2O3-water and Fe2O3-water) by the experimental analysis of thermal conductivity and dynamic viscosity for different concentrations; an experimental apparatus for the acquisition of sessile droplet images was designed in order to analyze the contact angle and wettability; and a computational routine was developed to obtain the drop profile and the surface-fluid interaction for the different nanofluids and surfaces used. Based on database, it was possible to evaluate the pre... (Complete abstract click electronic access below) / Doutor

O presente trabalho envolve a análise experimental do efeito da deposição de nanopartículas por meio da ebulição em piscina na molhabilidade e na textura da superfície. Inicialmente, este estudo apresenta uma análise da literatura sobre métodos de avaliação do ângulo de contato, preparo de nanofluidos, procedimentos de avaliação da rugosidade e possíveis efeitos que a deposição de nanopartículas tem sobre a textura da superfície. Verificou-se para as superfícies recobertas com nanopartículas ângulos de contato próximos a zero e comportamento dinâmico para gotas de água depositadas sobre elas. Desta forma, optou-se por avaliar a molhabilidade qualitativamente através da análise da velocidade de espalhamento de uma gota depositada sobre a superfície recoberta. Caracterizou-se também a massa de nanopartículas depositadas, a morfologia e a rugosidade das superfícies. Efetuou-se o recobrimento das superfícies por meio da ebulição em piscina de nanofluidos a base de água deionizada contendo nanopartículas de Al2O3 (10, 20-30 e 40-80 nm), Cu (25 nm) e SiO2 (15 e 80 nm) para concentrações volumétricas de 0,001, 0,01, 0,1 e 0,5%, submetidos a tempos de ebulição de 15, 30, 45 e 180 minutos em superfícies de alumínio e aço inoxidável. Como resultado final deste estudo concluiu-se que a rugosidade superficial e a molhabilidade se elevam com a deposição das nanopartículas. Além disso, a molhabilidade aumenta com o incremento da área da superfície recoberta com aglomerados. / The present study concerns an investigation on the wettability and the surface texture behavior of flat aluminum and stainless steel plates covered with porous thin-films of nanoparticles obtained through pool boiling of nanofluids. Since the contact angle of the obtained surfaces is small and in many cases the deposited droplet exhibits a dynamic behavior, dynamic top-down analyses of spreading droplets were performed. Evaluations were performed of nanoparticles mass deposition on the sample, surface roughness and micro-structural with an SEM (Scanning Electron Microscopy). Experiments were performed for nanofluids containing nanoparticles of Al2O3 (10, 20-30 and 40-80 nm), Cu (25nm) and SiO2 (15 and 80 nm) for volumetric concentrations of 0.001, 0.01, 0.1 and 0.5% for pool boiling time set to 15, 30, 45 and 180 minutes over aluminum and stainless steel plates. As a final result of this study it was found that surface roughness and wettability increase with the deposition of the nanoparticles. In addition, the wettability increases with increasing of the surface area covered with clusters.