Axial piston pumps and motors are widely used in heavy-duty applications and play a fundamental role in hydrostatic and power split drives. The mechanical power losses in hydraulic piston pumps come from the friction between parts in relative motion. The improvement, albeit marginal, in overall efficiency of these components may significantly impact the global efficiency of the machine. The friction between slipper and swash plate is a functional key in an axial piston pump, especially when the pump (at low rotational speed or at partial displacement) works in the critical areas where the efficiency is low. The application of special surface treatments have been exploited in pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers. The potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Due to the difficulty to reproduce the real working conditions of axial piston pump slippers, it has been made a hydraulic test bench properly designed in order to compare the performance of nano-coated slippers with respect to standard ones. The nano-coated and standard slippers have been subjected to the following working conditions: a test at variable pressure and constant rotational speed, a test at constant pressure and variable rotational speed. The comparison between standard and nanocoated slippers, for both working conditions, shows clearly that more than 20% of friction reduction can be achieved using the proposed nano-coating methodology.

Self-cleaning, anti-corrosion, anti-icing, dropwise-condensation, and drag-reduction are some applications in which superhydrophobic surfaces are implemented. To date, all the studies associated with superhydrophobic surfaces have been dedicated to understanding the liquid interaction with surfaces that are macroscopically smooth. The current study investigates the solid-liquid interaction of such surfaces which are fully decorated with macroscopic ridges (ribbed surfaces). In particular, the drop motion and impact on our newly designed non-wettable ribbed surface have been investigated in this work. Our experimental investigations have shown that liquid drops move faster on the ribbed surfaces due to lower friction induced by such a surface pattern. Moreover, an impacting droplet shows shorter contact time on ribbed surfaces. This concludes that ribbed surface pattern can be an efficient alternative design for the related applications. Besides the experimental studies, the theoretical analyses done in this work have led to, firstly a scaling model to predict descent velocity of a rolling viscous drops on an inclined non-wettable surface more accurately. Secondly, for curved superhydrophobic surfaces a scaling model which correlates the contact time of the impacting drop to its impact velocity has been developed. At the end, the knowledge obtained from this work has led to a special surface design which exhibits a contact time shorter than the inertial-capillary time scale, an unprecedented phenomenon.

The aim of this study has been to prepare and characterise oil resistant cellulosic materials, ranging from model surfaces to papers and aerogels. The cellulosic materials were made oil resistant by chemical and topographic modifications, based on surface energy, surface roughness and barrier approaches. Detailed wetting studies of the prepared cellulosic materials were made using contact angle measurements and standardised penetration tests with different alkanes and oil mixtures. A significant part of the activities were devoted to the development of model cellulosic surfaces with different degrees of crystalline ordering for the wetting studies. Crystalline cellulose I, II and amorphous cellulose surfaces were prepared by spin-coating of cellulose nanocrystal or microfibrillated cellulose (MFC) dispersions, with Langmuir-Schaefer (LS) films or by a layer-by-layer (LbL) deposition technique. The formation of multilayers consisting of polyethyleneimine (PEI)/anionic MFC or cationic MFC/anionic MFC was further studied and optimized in terms of total layer thickness and adsorbed amount by combining Dual Polarization Interferometry (DPI) or Stagnation Point Adsorption Reflectrometry (SPAR) with a Quartz Crystal Microbalance with Dissipation (QCM-D). The smooth cellulosic surfaces prepared had different molecular and mesostructure properties and different surface energies as shown by X-ray diffraction, Atomic Force Microscopy (AFM) imaging, ellipsometry measurements and contact angle measurements. The cellulose model surfaces were found to be ideal for detailed wetting studies, and after the surface has been coated or covalently modified with various amounts of fluorosurfactants, the fluorinated cellulose films were used to follow the spreading mechanisms of different oil mixtures. The viscosity and surface tension of the oil mixtures, as well as the dispersive surface energy of the cellulose surfaces, were found to be essential parameters governing the spreading kinetics. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the measured contact angle of the oil mixtures. Silicon surfaces possessing structural porous characteristics were fabricated by a plasma etching process. The structured silicon surfaces were coated with sulfate-stabilized cellulose I nanocrystals using the LbL technique. These artificial intrinsically oleophilic cellulose surfaces were made highly oleophobic when coated with a thin layer of fluorinated silanes. By comparison with flat cellulose surfaces, which are oleophilic, it is demonstrated that the surface energy and the surface texture are essential factors preventing oil from spreading on the surface and, thus, inducing the observed macroscopic oleophobic properties. The use of the MFC for surface coating on base papers demonstrated very promising characteristics as packaging materials. Environmental-Scanning Electron Microscopy (E-SEM) micrographs indicated that the MFC layer reduced the sheet porosity, i.e. the dense structure formed by the nanofibers resulted in superior oil barrier properties. Attempts were made to link the procedure for preparation of the MFC dispersions to the resulting microstructure of the coatings, and film porosity and the film moisture content to the resulting permeability properties. Finally, MFC aerogels were successfully prepared by freeze-drying. The surface texture of the porous aerogels was carefully controlled by adjusting the concentration of the MFC dispersion used for the freeze-drying. The different scales of roughness of the MFC aerogels were utilised, together with the very low surface energy created by fluorination of the aerogel, to induce highly oleophobic properties. / QC 20100623

Axial piston pumps and motors are widely used in heavy-duty applications and play a fundamental role in hydrostatic and power split drives. The mechanical power losses in hydraulic piston pumps come from the friction between parts in relative motion. The improvement, albeit marginal, in overall efficiency of these components may significantly impact the global efficiency of the machine. The friction between slipper and swash plate is a functional key in an axial piston pump, especially when the pump (at low rotational speed or at partial displacement) works in the critical areas where the efficiency is low. The application of special surface treatments have been exploited in pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers. The potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Due to the difficulty to reproduce the real working conditions of axial piston pump slippers, it has been made a hydraulic test bench properly designed in order to compare the performance of nano-coated slippers with respect to standard ones. The nano-coated and standard slippers have been subjected to the following working conditions: a test at variable pressure and constant rotational speed, a test at constant pressure and variable rotational speed. The comparison between standard and nanocoated slippers, for both working conditions, shows clearly that more than 20% of friction reduction can be achieved using the proposed nano-coating methodology.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18096号 / 理博第3974号 / 新制||理||1573(附属図書館) / 30954 / 京都大学大学院理学研究科化学専攻 / (主査)准教授 中西 和樹, 教授 北川 宏, 教授 竹腰 清乃理 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Le travail de la thèse est focalisé sur l’ élaboration plasma d’un revêtement multicouches avec une couche supérieure anti-brouillard et une couche inférieure dite barrière sur un polycarbonate. L’ensemble des travaux est divisé en 3 parties: élaborations des deux monocouches barrière ou antibuée puis dépôt de la multicouche barrière - antibuée. La polymérisation plasma de la couche barrière est effectuée à partir d’un mélange de dioxygène et d’un précurseur organosilicié : l’hexaméthyledisiloxane ou le 2,4,6,8-tétraméthylcyclotétrasiloxane ou bien encore le triéthoxyfluorosilane. La caractérisation des couches minces obtenues repose sur la spectroscopie Infrarouge à Transformée de Fourier , la spectroscopie de photoélectrons X et la microscopie à force atomique. L’influence des conditions de dépôt plasma comme la puissance, la proportion monomère/dioxygène, le temps du dépôt sur la structure chimique et l’hydrophobicité de la surface des différents types de couches organosiliciées est étudiée. Les résultats de la perméation avec l’eau liquide ou le dioxygène montrent que la propriété barrière des couches organosiliciées non fluorées est meilleure que pour la couche fluorée. L’élaboration de copolymères anti-buée repose sur l’utilisation de combinaisons entre deux précurseurs hydrophile et hydrophobe en voie plasma pulsé. Les précurseurs tels que le 2-(diméthylamino)éthyl méthacrylate ou l’acide acrylique sont choisis pour leur hydrophile alors que le 1H,1H,2H-perfluoro-1-décène représente la partie oléophobe. La propriété anti-brouillard et sa stabilité à long terme après un vieillissement thermique ou en milieu humide est dépendante de leurs structure et morphologie. / The PhD work is focused on the deposition of a multilayer coating with an anti-fog top layer obtained thanks to the plasma copolymerization of hydrophilic and hydrophobic monomers and an intermediate barrier layer, also obtained by plasma deposition on polycarbonate. The work is divided into 3 parts: the independently preparations of the two monolayers, barrier and anti-fogging ones, then the barrier-antifog multilayer deposition. The characterization of the thin films obtained is based on Fourier Transform Infrared Spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy.The barrier plasma-layer is issued from by the mixture of dioxygen and one of these three organosilicon precursors : hexamethyledisiloxane ; 2,4,6,8-tetramethylcyclotetrasiloxane ; triethoxyfluorosilane. The influence of the plasma conditions such as discharge power, monomer/dioxygen ratio, deposition duration on the chemical structure and the hydrophobicity of the different types of the organosilicon layers was studied. The results of permeation with liquid water or dioxygen show that the barrier property of the organosilicon layer is more efficient than that of the fluorinated layer. Anti-fog plasma-copolymer is synthetized from two hydrophilic and hydrophobic precursors deposited by pulsed plasma mode. The precursors such as 2-(dimethylamino) ethyl methacrylate and acrylic acid were selected for the hydrophilic part while the 1H, 1H, 2H-perfluoro-1-decene will be associated to the oleophobic part. The dependence of the chemical structure and the morphology of the anti-fog layers is studied according to the hydrophilic/oleophobic distribution and the deposition time.

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