This study focuses on fabrication of dry adhesives mimicking gecko adhesion. We also look into the origin of the supreme adhesion of geckos, which have inspired the fabrication of fibrillar dry adhesives during the last decade or so. In principle, the superior material properties of ??-keratin (the main material comprising the fibrillar feature on gecko toe pads) along with the hierarchical high aspect-ratio fibrillar structure of geckos??? foot pad have enabled geckos to stick readily and rapidly to almost any surface in both dry and wet conditions. In this research, non-sticky fluoropolymer (Teflon AF) resembling ??-keratin rigidity and having an extremely low surface energy and dielectric constant was applied to fabricate a novel dry adhesive consisting of extremely high aspect-ratio nanopillars (200 nm in diameter) terminated with a fluffy top nanolayer. Both the nanopillars and the terminating layer were fabricated concurrently by replica-molding using a nanoporous anodic aluminum oxide membrane as the mold. In particular, upon infiltration of Teflon AF melt into the anodic aluminum oxide nanopores, the polymer melt fingered over the pore walls. The fingerlike structure formed during infiltration, subsequently collapsed after removal of the mold, developing a unique sheet-like nanostructure on top of the base nanopillars. Concurrent fabrication of the terminating nanostructure helps the fabrication of extremely high aspect-ratio (27.5???225) nanopillars which, up to an aspect-ratio of 185, neither collapse at the tip nor bundle. In order to fabricate nanopillars of different topographical properties, in our first approach, the height of the nanopillars as well as the size and density of the terminating nanostructure are carefully controlled by adjusting the processing temperature. Following that, a novel replica-molding technique for fabrication of bi-level Teflon AF nanopillars is reported. The developed technique relies on the concurrent heating and cooling of the Teflon AF melt which filled vertically-aligned alumina nanochannels. Unlike conventional polymer infiltration methods which consist of filling the mold by only heating the polymer above its glass transition temperature, in our novel method, the polymer melt is also simultaneously cooled down during the infiltration process. Concurrent cooling of the Teflon AF melt allows control over the interfacial instabilities of the polymer thin film, which forms ahead of the polymer melt upon its infiltration into the alumina nanochannels. Doing so, the geometrical properties of the subsequently developed peculiar fluffy nanostructure ??? after removal of the mold ??? on top of the extremely high aspect-ratio Teflon AF nanopillars (~25 ??m tall) are modified. In this project, we have also shown that the adhesion of the fabricated dry adhesives for the most part arises from electrostatic interactions of the applied polymer. In other words, Teflon AF, having an exceptional potential for developing electric charges at its surface upon contact with other materials via the so-called contact electrification phenomenon, can develop significant electrostatic interactions at its surface upon contact. In the current thesis, tribological results were discussed in detail to clarify the contribution of the structural properties of the fabricated dry adhesives toward their remarkable adhesion and friction forces generated via contact electrification. Nanopillars of specific geometrical properties have achieved remarkable adhesion and friction strengths, up to ~2.1 N/cm2 and 17 N/cm2, respectively (up to ~2.1 and 1.7 times larger than those of a gecko toe pad). It is commonly accepted that the adhesive performance of other synthetic bio-inspired dry adhesives is due to the formation of van der Waals interactions at the tip or side of the dry adhesives fibrils with the substrate they are brought into contact with. However, what has been usually neglected in this connection is that electrostatic interactions may also be developed at the contact between any two materials via the familiar contact electrification phenomenon. Although contact electrification is common and can have a large influence on interfacial interaction forces, its impact on adhesive properties of synthetic dry adhesives has been overlooked. Our results on adhesion of bi-level Teflon AF nanopillars, which can generate strong adhesion forces relying on electrostatic interactions arising from contact electrification, have brought to light again the idea that charging the surface of dry adhesives, specifically polymeric ones, can play a very crucial role in their adhesive behavior. From this perspective, the main reasons that have caused this lack of attention to this concept and the possible contributions of contact electrification to interfacial interactions of polymeric dry adhesives, other than bi-level Teflon AF nanopillars, are also thoroughly discussed in this thesis. Besides synthetic fibrillar dry adhesives, the possibility of the occurrence of contact electrification and its contribution to the supreme dry adhesion of geckos have also been overlooked for several decades. In this research, by the simultaneous measurement of electric charges and adhesion forces that gecko toe pads develop on two distinct substrates (a sticky and a non-sticky one), we have shown that the toe pads generate significantly large amounts of electric charge on both substrates. More importantly, we have found that there is a direct correlation between the contact electrification-driven electrostatic forces and the measured adhesion forces. Otherwise stated, we have shown that what makes the difference that geckos stick strongly to one surface and not to the other are the electrostatic interactions arising from contact electrification, and not van der Waals interactions, which have been considered as the prime source of adhesion of geckos for many years.

No description available.

As rail transportation is significantly more virtuous than airplanes or cars in terms of greenhousegases emissions, its development is being encouraged in several European countries, includingSweden. In addition, the development of railway lines on which trains can travel at higher speeds ismade in Sweden with the integration of existing infrastructure. On railway bridges, an increased trainspeed potentially leads to an increase in vibrations during passage, for which the structure may not bedesigned. It is therefore essential to know the dynamic properties of the structures used.Several studies highlight the influence of friction phenomena in sliding bearings on the dynamicproperties of bridges equipped with them. This Master Thesis is based on previous works that led tothe development of a finite element modelling the friction mechanisms that occur in these bearings.The friction occurring between a PTFE sliding plate and a steel surface is thus modelled using the Bouc-Wen model, a model for hysteresis phenomena. The finite element was developed as a Fortransubroutine, which can be integrated into the finite element calculation software Abaqus as a "userdefinedelement". It allows friction to be modelled along the longitudinal direction of the bridge onlyand can therefore only be used in two-dimensional models. The user-defined element is also based ona model that takes into account the influence of contact pressure and sliding velocity on the steel-PTFEcoefficient of friction. As several studies indicate, contact temperature can also have a significantinfluence on the value of the coefficient of friction but is not taken into account in the current model.In this project, the previously developed finite element was therefore generalized to account forfriction in both directions of the sliding plate by the means of a two-dimensional generalization of theBouc-Wen model. Based on experimental data available in scientific literature, the model forcalculating the coefficient of friction was also extended to take into account the influence of thecontact temperature. In addition, a model to update the contact temperature based on the theory ofsurface heating of semi-infinite bodies has been incorporated. Finally, this thesis presents theintegration of this updated finite element on three-dimensional models of the Banafjäl Bridge, locatedin northern Sweden. Simulations to estimate the fundamental frequencies and resonance modes ofthe structure as well as the temperature increase that can occur in a bearing during the passage of atrain were carried out on this model.

Le développement de méthodologies permettant de fonctionnaliser aisément les surfaces est un domaine en plein essor. Nous avons synthétisé et caractérisé de nouveaux complexes de cuivre(II)-carboxylates hautement fluorophiles qui ont été utilisés pour modifier des surfaces. Ces complexes possèdent à l'état solide une très grande affinité pour l'eau, l'hydratation induisant un changement radical des propriétés magnétiques du solide. Ces complexes fluorophiles s'adsorbent très fortement sur le Téflon ou sur le verre pour conduire à des surfaces hydrophiles et coordinantes. En utilisant la chimie de coordination, les surfaces ont ensuite été fonctionnalisées. Des monocouches et des couches minces de porphyrines ont été obtenues sur le verre et sur le téflon puis caractérisées, notamment grâce à leurs propriétés optiques. / The development of methodologies to easily functionalize surfaces is a fast growing field. We have synthesized and characterized new highly fluorophilic copper(II)-carboxylate complexes that have been employed to modify surfaces. In the solid state, these complexes exhibit a high affinity for water, the hydration process inducing dramatic modifications of their magnetic properties. These fluorophilic complexes are strongly adsorbed on teflon or glass to afford hydrophilic and coordinating surfaces. Using coordination chemistry, the surfaces can than be functionalized. Porphyrins monolayers and thin layers have been prepared on glass and teflon and characterized, in particular by their optical properties.

The present thesis deals with optimization of the formation of thin layers of metallic materials. In the theoretical part was elaborated overview of the implementation of the formation of thin- film structures, particularly using vacuum techniques. Chemical and physical vapor deposition. They were described methods of pretreatment of thin layers. The findings were discussed methods of controlling the pre-treated surface, quality control and mutual adhesion of coating layers. In the experimental part of the pre-treatment methods were selected and applied to selected substrates. Pretreatments were evaluated using a control surface by wetting angles and by atomic force microscopy. Then, the metal structure formed of copper on the pretreated substrates. Implementation by means of magnetron sputtering. Adhesion layers was checked by testing the surface lattice method. The quality was observed by scanning electron microscopy. The results were used to design the technological process of making metal layers.

No description available.