Capillarity is often exploited in self-cleaning, drag reducing and fluid absorption/storage (sanitary products) purposes just to name a few. Formulating the underlying physics of capillarity helps future design and development of optimized structures. This work reports on developing computational models to quantify the capillary pressure and capillary forces on the fibrous surfaces. To this end, the current study utilizes a novel mass-spring-damper approach to incorporate the mechanical properties of the fibers in generating virtual fibrous structures that can best represent fibrous membranes. Such virtual fibrous structures are then subjected to a pressure estimation model, developed for the first time in this work, to estimate the liquid entry pressure (LEP) for a hydrophobic fibrous membrane. As for accurate prediction (and not just estimation) of the capillary pressure, this work also presents an energy minimization method, implemented in the Surface Evolver code, for tracking the air–water interface intrusion in a hydrophobic fibrous membrane comprised of orthogonally oriented fibers. This novel interface tracking algorithm is used to investigate the effects of the membrane’s microstructure and wetting properties on its resistance to water intrusion (i.e., LEP). The simulation method developed in this work is computationally affordable and it is accurate in its predictions of the air–water interface shape and position inside the membrane as a function of pressure. Application of the simulation method in studying effects of fiber diameter or contact angle heterogeneity on water intrusion pressure is reported for demonstration purposes. Capillary forces between fibrous surfaces are also studied experimentally and numerically via the liquid bridge between two parallel plates coated with electrospun fibers. In the experiment, a droplet was placed on one of the polystyrene- or polyurethane-coated plates and then compressed, stretched, or sheared using the other plate and the force was measured using a sensitive scale. In the simulation, the liquid bridge was mathematically defined for the Surface Evolver finite element code to predict its 3-D shape and resistance to normal and shearing forces, respectively, in presence of the contact angle hysteresis effect. Despite the inherent non-uniformity of the fibrous surfaces used in the experiments and the simplifying assumptions considered for the simulations, reasonable agreement was observed between the experiments and simulations. Results reveal that both normal and shear force on the plates increase by increasing the liquid volume, or decreasing the spacing between the plates.

In this thesis detailed investigations of the phase behavior of poly(n-alkyl methacrylate-b-methyl methacrylate) diblock copolymers and its influence on the wettability of the polymer surfaces were carried out. For this investigation two polymethacrylic systems differing only in the alkyl rest of one block: poly(pentyl methacrylate-b-methyl methacrylate) and poly(propyl methacrylate-b-methyl methacrylate) have been chosen in order to prove how this substituent affects the phase behavior of whole system. The PnAlkMA-b-PMMA diblock copolymers in a wide range of molar masses, and with varied block length ratios were synthesized by living anionic polymerization. The syntheses were carried out in tetrahydrofuran (THF), at –78 °C, by using sec-buthyllithium as initiator, in the presence of lithium chloride (LiCl). Under these conditions highly syndiotactic products, rr ~ 0.82, with very narrow molar mass distribution, Mw/Mn ~ 1.1, were obtained. The phase behavior of PnAlkMA-b-PMMA diblock copolymers in bulk was investigated by means of DSC and SAXS measurements. The DSC analysis revealed that the PPMA-b-PMMA with weight fractions of PPMA, fPPMA, from 0.28 up to 0.86 showed two separate Tg’s, indicative of a phase separated system. However, by comparing the Tg’s of the diblock copolymers with the Tg’s of the corresponding homopolymers we found that in a few cases, mostly for samples with the high molar masses, they were slightly shifted. This finding pointed out the existence of two mixed phases, and hence partial miscibility between the both blocks was assumed. The SAXS patterns reflected for most diblock copolymers lamellae morphologies even in the case of very asymmetric composition, for instance with volume fraction of PPMA, 0.86 It was assumed that this behavior is caused by the chemical similarity of both blocks as well as by the differences in their molar volumes. The SAXS findings were further confirmed by the AFM measurements on the cutted “bulk” samples. From the solubility concept of Van Krevelen we obtained that the interaction parameter of PPMA-b-PMMA is rather low, 0.065, compared to the other well-known diblock copolymers. The calculated spinodals are characterized by a high asymmetry. The investigation of the phase behavior of PPMA-b-PMMA in thin films showed that the morphology as well as the topography of the thin films were strongly affected by the film thickness, when the films were prepared from a non-selective solvent (THF) onto silicon wafers. Well-recognizable nanostructures with long-range order were mainly found in thin films of diblock copolymers with high molar masses, above 100,000 g/mol, and with a high amount of PPMA. The lateral domain spacing obtained for these films from AFM corresponded well with that found in bulk. The study of the influence of the thermal as well as vapor annealing on the morphology and topography of the thin films provided additional information about the phase behavior of PPMA-b-PMMA diblock copolymers in thin films. Finally, the wettability of the investigated PPMA-b-PMMA surfaces was established by means of contact angle measurements. The measured contact angles were in most cases even on nicely nanostructured surfaces very similar to the contact angle of PPMA, indicating preferential segregation of PPMA to the film surface. Additional XPS measurements also showed an enrichment of the PPMA at the surface, independent of the morphology observed by AFM, and thereby confirmed the ADSA finding. In the next part of this work, investigations of the phase behavior of PPrMA-b-PMMA diblock copolymers were presented. In the contrary to the previous system the PPrMA-b-PMMA showed mostly a single Tg, which was further found to be depend on the weight fraction of PPrMA, fPPrMA. The SAXS data revealed that the PPrMA-b-PMMA diblock copolymers were phase separated in bulk, however the obtained scattering patterns exhibited mostly broad, not-well discernible higher-order peaks. Nevertheless, it was possible to identify the formed morphologies and depending on the volume fraction of PPrMA, hexagonally packed cylinders and lamellae were detected. The PPrMA-b-PMMA is characterized by a significantly lower value of the interaction parameter, 0.022, than the PPMA-b-PMMA system. This difference clearly reflects the weakening of the interactions between the components with decrease of the length of the alkyl side chain. The thin films of PPrMA-b-PMMA diblock copolymers appeared mostly smooth and featureless, independent of the film thickness. From the contact angle and XPS measurements we obtained, that unlike the PPMA-b-PMMA, both components were always present on the top of the surface. / In der vorliegenden Arbeit wurden Untersuchungen zum Entmischungsverhalten von Poly(n-alkylmethacrylat-b-methylmethacrylat) Diblockcopolymeren und deren Einfluss auf die Benetzbarkeit der Polymeroberflächen dargestellt. Diese Untersuchungen wurden anhand der Poly(pentylmethacrylat-b-methylmethacrylat) und Poly(propylmethacrylat-b-methylmethacrylat) durchgeführt. Die Diblockcopolymere in einem weiten Molmassenbereich, mit enger Molmassenverteilung, abgestuften Zusammensetzung wurden erfolgreich mittels anionischer Polymerization synthetisiert. Die Synthese erfolgte in THF bei (-78 °C) in Gegenwart von Lithiumchlorid. Als Initiator wurde sec. Butyllithium genutzt. Das Phasenverhalten der Diblockcopolymere im Festkörper wurde mittels DSC und SAXS untersucht. Für die meiste PPMA-b-PMMA Diblockcopolymere wurden mittels DSC zwei getrennte Tg gefunden, die aber im Vergleich zu den Tg von den entsprechenden Homopolymeren leicht verschoben waren. Es wurde also eine partielle Mischbarkeit der Blöcke festgestellt. Mittels SAXS-Untersuchungen wurde für die Mehrzahl der Diblckcopolymere in einem weiten Zusammensetzungsbereich bis zum 0.86 Volumenanteil von PPMA, eine lamellare Anordnung beobachten. Diese Befunde wurden nachfolgend mit AFM–Untersuchungen an dünnen Polymerfolien bestätigt. Das mit der Mean-Filed-Methode berechnete Phasendiagramm zeigte eine Asymmetrie, die durch die Unterschiede in den molaren Volumina des Blöckes verursacht war. Es wurde aber eine gute Übereinstimmung mit der experimentell erhaltenen Daten gefunden. Der berechnete für das System Wechselwirkungsparameter beträgt 0,065. Die AFM-Untersuchungen zum Entmischungsverhalten in dünnen Filmen haben gezeigt, dass die Topographie als auch Morphologie des Films war von der Filmdicke beeinflusst. Die Polymerfilme wurden mittels dipcoating der Si-Wafer präpariert. Dazu wurden Polymerlösungen in THF verwendet. Reguläre Nanostrukturen, deren Abstände mit dem im Festkörper gefundenen sehr gut übereinstimmten, wurden bei den Proben mit höherem Anteil von PPMA erhalten. Es wurden auch der Einfluss der Temperatur und der Dampfbehandlung auf die Morphologie und Topographie des Films untersucht. Die Benetzbarkeit der untersuchte PPMA-b-PMMA Filme wurde mit der Kontaktwinkelmessungen (ADSA) bestimmt. Als Messflüssigkeit wurde Milipore Wasser genutzt. Für die Mehrzahl der Diblockcopolymere wurden Kontaktwinkel im Bereich um 95° ermitteln, unabhängig von der Zusammensetzung der Diblockcopolymere und der vorhandenen Nanostruktur. Dies entspricht dem Kontaktwinkel von PPMA Homopolymer. Die Benetzbarkeit der PPMA-b-PMMA Filme wurde also durch die Oberflächensegregation des Niedrigenergieblocks (PPMA) bestimmt. Dies wurde danach durch zusätzliche XPS Messungen bestätigt. Im Vergleich zu PPMA-b-PMMA, die nachfolgend untersuchte PPrMA-b-PMMA Diblockcopolymere wiesen eine höhere Tendenz zur Mischbarkeit auf. Anhand der DSC–Untersuchungen wurde hier vorübergehend eine Misch-Tg gefunden. Nur bei der Probe mit symmetrischer Zusammensetzung wurden zwei getrennte Tg beobachtet. Die Streukurven von diesem System waren sehr schwach ausgeprägt. Dadurch die Indizierung der vorhandenen Morphologien war nicht eindeutlich. Der berechnete Wechselwirkungsparameter beträgt 0,022. Bei den AFM-Untersuchungen zum Entmischungsverhalten in dünnen PPrMA-b-PMMA Filmen wurden entweder keine oder sehr schwach geordnete Nanostruktur gefunden. Im Gegensatz zu dem vorherigen System, die Benetzbarkeit der PPrMA-b-PMMA Filme war durch die Zusammensetzung der Diblockcopolymere bedingt.

Magnesium and its alloys have been considered for load-bearing implant materials due to their similar mechanical properties to the natural bone, excellent biocompatibility, good bioactivity, and biodegradation. Nevertheless, the uncontrollable corrosion rate in biological environment restrains their application. Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is a widely used bio-ceramic which has bone-like mineral structure for bone fixation. Poor fracture toughness of HA makes it not suitable for load-bearing application as a bulk. Thus, HA is introduced into metallic surface in various forms for improving biocompatibility. Recently friction stir processing (FSP) has emerged as a surface modification tool for surface/substrate grain refinement and homogenization of microstructure in biomaterial. In the pressent efforts, Mg-nHA composite surface on with 5-20 wt% HA on Mg substrate were fabricated by FSP for biodegradation and bioactivity study. The results of electrochemical measurement indicated that lower amount (~5% wt%) of Ca in Mg matrix can enhance surface localized corrosion resistance. The effects of microstructure,the presence of HA particle and Mg-Ca intermetallic phase precipitates on in vitro behavior of Mg alloy were investigated by TEM, SEM, EDX,XRD ,and XPS. The detailed observations will be discussed during presentation.

The erosion or dissolution of stainless steel grade 304 as base metal by molten brazing fillermetal was investigated using one nickel and two iron based filler metals. The difference betweentwo iron filler metal is 5 % Manganese content in one of the filler metal. The Wettability of fillermetal is effected by oxidation of base or filler metal for which high vacuum or non reacting gasis used as a furnace atmosphere to reduce the partial pressure of oxygen. The furnace parameterseffecting erosion of base metal was observed e.g. peak temperature and brazing time. The effectof filler mass was also observed. The erosion depth was measured by light optical microscope.All the three filler metal shows different erosion behavior in nitrogen atmosphere compare tohigh vacuum. In high vacuum some of the elements evaporates at brazing temperature whichchanges the properties of filler metal. This change of composition in filler metal was observed byEDX analysis. SEM analysis was used to identify different element rich phases.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21887号 / エネ博第388号 / 新制||エネ||75(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 齊藤 泰司, 教授 横峯 健彦, 准教授 伊藤 啓 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Additive Manufacturing (AM) has revolutionized manufacturing processes by enabling the realization of custom products with intricate geometric features that were either too complex or even intractable for subtractive manufacturing processes. Yet, functional surfaces generated in AM have to be often finish machined because of their relatively inferior roughness. The first phase of this research worked around this limitation by tailoring the topography of an AM surface in-process to entail textures that further enhance certain functionalities in a process called Additive Texturing (AT). In this context, the Selective Laser Melting (SLM) process ability to realize intricate surface microfeatures was explored experimentally, evaluating its geometrical limitations. Utilizing such limitations, various patterns comprising pillars, channels, and re-entrant structures were printed to control the wetting behaviour of SLM stainless steel. AT's efficacy is demonstrated in its capability to generate hydrophobic AM surfaces with water contact angles exceeding 140°. Similarly, other texturing patterns comprising dimples, linear, V-shaped, and X-shaped grooves were investigated to tailor the tribological response of textured surfaces under dry sliding conditions. Evidently, a specific wear rate and coefficient of friction reduction of 80% and 60%, respectively, demonstrated another potential for AT. The undesirable tensile Residual Stresses (RS) that inevitably accumulate during the SLM process's rapid heating and cooling cycles were investigated in the second phase of this research. Laser Peening (LP) was utilized to post-process the printed samples to eliminate the initial tensile RS and induce near 500 Mpa compressive RS. Moreover, the LP parameters were explored and optimized to enhance RS, surface roughness, hardness, and wear resistance. / Thesis / Doctor of Philosophy (PhD)

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / The developed oil-water separation membranes used in membrane technology are currently inefficient due to their poor morphological and topographical properties during nanoparticle coating. Researchers have developed different wettable membrane surfaces using jet spray coating. Most of these developed membranes are inadequate due to poor morphological and topographical properties normally observed as clusters, creating a rougher membrane surface that hinders wettability. This has resulted in the existing membrane fouling and degradation during the oil/water separation process and again due to different responses to corrosion and rusting. In the current study, membrane clusters were minimised on the ceramic membranes to create a smoother surface, improving membrane wettability. These clusters were minmised at optimal coating force, optimal coating distance and optimal coating angle. Part one of the study was to model and simulate different parameters that decreased clusters using the jet-spray coating. A theoretical model was derived from the first principles and all the external and internal forces that impact membrane clusters were considered during the model derivation. These forces are the force due to applied pressure from the spray gun, the force of nano-particles, the force of viscosity, the upward force on solid wall due to nanoparticles, the downward force on solid wall due to nanoparticles and the reaction force on the solid wall due to nanoparticles. The tools of stochastic theory and the concept of fluid dynamics were used in the modelling process. The total coating force from the jet spray gun nozzle was increased from 0,2x107 kN to 2,4x107 kN, which gave optimal coating force. The coating distance from the jet spray gun nozzle to the membrane surface was increased from 10 mm to 24 mm, which gave optimal coating distance. The jet spray angle in the spray region was also increased from 1⁰ to 9⁰ with reference from the vertical axis to the membrane surface, which gave optimal coating angle. This lead to optimal spread of nanoparticles on the membrane surface thus resulting to optimal cluster minimisation during the coating process. This decreased cluster sizes during nanoparticle coating, resulting in a smooth membrane surface, thus leading to lowered surface energy on the membrane. Part two of the study was to fabricate the ceramic membrane with fewer clusters on the surface for improved wettability using the jet-spray coating. It was important to produce the ceramic membrane surfaces with minimised membrane clusters by considering the optimal parameters revealed to minimise these membrane clusters during coating. Nanoparticle coating was performed under a controlled laboratory environment, and the optimal parameters that were studied to minimise membrane clusters were revealed. These parameters are coating force, coating distance and coating angle. More coating rounds were applied on ceramic samples and clusters were minimised during these coating rounds. The coated samples were analyzed by a scanning electron microscope and the nanoparticles on the membrane surfaces were characterised for optimal performance during oil-water separation. The scattering, orientation, morphology, spatial distribution, surface roughness, surface smoothness, contact angles, surface density of the particles, pore size network, mean size of the coated nanoparticle on the membrane surface after different coating rounds were characterised and analysed to minimise membrane cluster during nanoparticle coating. It was shown that more clusters were observed in 1st LP, 2nd LP, 3rd LP and 4th LP coating rounds when compared to 1st HP, 2nd HP, 3rd HP and 4th HP coating rounds. It was also shown that material surface roughness increased the formation of clusters in membrane surface as more clusters were observed in rough membrane surface when compared to the smooth membrane surface. The microstructure revealed a smoother membrane surface where membrane clusters were minimised. Part three of the study was to compare the newly designed ceramic membrane with the previously designed ceramic membrane from previous the literature. The correlation was done on the experimental results obtained in this study with the experimental results obtained from the previous literature. Different coating rounds were performed from the current study and the previous literature to design nanostructured ceramic membranes with fewer clusters on the surface. The results in the last coating round in this study, revealed a smooth membrane with a homogeneous substrate with fewer clusters and small sizes compared to other coating rounds.

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