Showing papers by "Eduard Arzt published in 2010"

Gecko-inspired surfaces: a path to strong and reversible dry adhesives.

Abstract: The amazing adhesion of gecko pads to almost any kind of surfaces has inspired a very active research direction over the last decade: the investigation of how geckos achieve this feat and how this knowledge can be turned into new strategies to reversibly join surfaces. This article reviews the fabrication approaches used so far for the creation of micro- and nanostructured fibrillar surfaces with adhesive properties. In the light of the pertinent contact mechanics, the adhesive properties are presented and discussed. The decisive design parameters are fiber radius and aspect ratio, tilt angle, hierarchical arrangement and the effect of the backing layer. Also first responsive systems that allow thermal switching between nonadhesive and adhesive states are described. These structures show a high potential of application, providing the remaining issues of robustness, reliability, and large-area manufacture can be solved.

Functional Adhesive Surfaces with “Gecko” Effect: The Concept of Contact Splitting

Abstract: Nature has developed reversibly adhesive surfaces whose stickiness has attracted much research attention over the last decade. The central lesson from nature is that “patterned” or “fibrillar” surfaces can produce higher adhesion forces to flat and rough substrates than smooth surfaces. This paper critically examines the principles behind fibrillar adhesion from a contact mechanics perspective, where much progress has been made in recent years. The benefits derived from “contact splitting” into fibrils are separated into extrinsic/intrinsic contributions from fibril deformation, adaptability to rough surfaces, size effects due to surface-to-volume ratio, uniformity of stress distribution, and defect-controlled adhesion. Another section covers essential considerations for reliable and reproducible adhesion testing, where better standardization is still required. It is argued that, in view of the large number of parameters, a thorough understanding of adhesion effects is required to enable the fabrication of reliable adhesive surfaces based on biological examples.

Adhesion Characteristics of PDMS Surfaces During Repeated Pull‐Off Force Measurements

Abstract: To mimic the adhesive effects of gecko toes, artificial surfaces have been manufactured recently using polydimethylsiloxanes (PDMS). However, the effects of repeated contacts on the adhesive properties remain largely unexplored. In this paper we report on the effect of repeated pull-off force measurements on the adhesion behavior of PDMS (polymer kit Sylgard 184, Dow Corning) tested with a borosilicate glass probe. A decrease in pull-off force with increase in number of test cycles is found until a plateau is reached. The initial value and the rate of change in pull-off force strongly depend on the sample preparation procedure, including curing time and cross-linking. It is proposed that the behavior is due to steady coverage of the probe with free oligomers. The results are crucial for developing reusable, durable, and residue-free bioinspired adhesives.

Strength effects in micropillars of a dispersion strengthened superalloy

Abstract: The present paper investigates the uniaxial compression behavior of highly alloyed, focused ion beam (FIB) manufactured micropillars, ranging from 200 up to 4000 nm in diameter. The material used was the Ni-based oxide-dispersion strengthened (ODS) alloy Inconel MA6000. Stress–strain curves show a change in slip behavior comparable to those observed in pure fcc metals. Contrary to pure Ni pillar experiments, high critical resolved shear stress (CRSS) values were found independent of pillar diameter. This suggests that the deformation behavior is primarily controlled by the internal obstacle spacing, overwhelming any pillar-size-dependent mechanisms such as dislocation source action or starvation.

Nanofibrillar Patterns by Plasma Etching: The Influence of Polymer Crystallinity and Orientation in Surface Morphology

Abstract: This manuscript explores the possibility of exploiting polymer morphology (thermal or flow-induced) as materials inherent template, and domain-selective plasma etching as pattern developer, to obtain nanopatterned surfaces with different and controlled geometries, with a particular focus on nanofibrillar patterns. Oxidative plasma treatment of PET films has rendered patterned surfaces with different geometries depending on the crystallinity and orientation of the PET sample and plasma treatment time (or etching ratio). Homogeneous patterns with either randomly distributed or aligned nanofibrils with diameters between 20 and 40 nm and lengths up to 1 μm (after extensive etching) were observed depending on the sample pretreatment. Our results demonstrate the potential of oxidative plasmas as templateless nanopatterning technique and reveal a complex interplay between plasma etching parameters and polymer microstructure driving the pattern formation mechanism. These results open the possibility of fabricatin...

Discrete contact mechanics of a fibrillar surface with backing layer interactions

Abstract: The contact mechanics of a fibrillar micro-fabricated surface structure made of poly(dimethyl siloxane) (PDMS) is studied. The attachment and detachment of individual fibrils to and from a spherical indenter upon approach and retraction are detected as jumps in force and stiffness. A quantitative model describes the stiffness values by taking into account the deformation of the fibrils and the backing layer. The results emphasize the importance of long-range interactions in the contact mechanics of elastic materials and confirm some of the important concepts underlying the development of fibrillar adhesive materials.

Effect of pre-straining on the size effect in molybdenum pillars

Abstract: The effect of prior deformation on mechanical behavior as a function of size is investigated for body-centered cubic (bcc) molybdenum (Mo) pillars. Experiments were performed using focused ion beam (FIB) manufactured [0 0 1] and [2 3 5] Mo micro/nanopillars, which were compressed, re-FIB machined, and compressed again. Unlike in bulk materials, pre-straining has a negligible effect on stress–strain behavior of the pillars, suggesting that dislocation storage does not occur in small-scale bcc specimens. The prevailing mechanism behind the size effect is attributed to dislocation nucleation mechanisms.

Bi‐Stable Adhesion of a Surface with a Dimple

Abstract: In this paper, we propose a new adhesive system of dimpled surfaces. The principle is derived from a contact mechanics model. The material is assumed to be linear elastic and isotropic, and attraction between the surfaces of the half-spaces is modeled via the concept of a specific adhesion energy. It is found that large and small detachments are unstable and will either grow or shrink spontaneously when their sizes are perturbed. It is shown that this phenomenon can lead to a new bi-stable adhesive system in which weak adhesion can be converted to strong adhesion by the application of pressure.

Nanoindentation studies on crosslinking and curing effects of PDMS

Abstract: Nanoindentation testing was used to investigate the mechanical properties of PDMS focusing on two aspects: Firstly, the results give a comprehensive overview of the mechanical behavior of PDMS Sylgard 184 which guides the property tailoring for many different application fields, where the mechanical behavior needs to be considered, but is not readily accessible. Secondly, the ability to measure the slight differences in the mechanical properties of these PDMS samples emphasized the high sensitivity of this technique and underlined its reliability for application on very compliant materials. The indentation results obtained in this study did not deviate from complementary tensile test data more than 5%. It was found that the elastic moduli of differently crosslinked samples cover a range of 2 orders of magnitude; for one and the same PDMS the modulus may increase 10-fold as a function of curing time.

Modeling the effects of nanoparticles on neuronal cells: From ionic channels to network dynamics

Abstract: Engineered nanoparticles (NPs) offer great application potential in various fields, for example the chemical industry, energy management or medical sciences. Nanoparticles are increasingly being incorporated into daily products. But what happens, if living organisms are exposed to those NPs? Their ability to move seemingly barrier-free in organic tissue could be both beneficial and harmful. Even though research concerning nanotoxicity has already begun, there are still many open questions to be addressed. In this report, we propose a computational model applying the steady-state Hodgkin-Huxley-equations and the Differential Evolution Algorithm for fitting the model to the data of patch-clamp measurements carried out by our group: Coated silvernanoparticles (Ag-Nano) in different concentrations were applied to single chromaffin cells while measuring the ionic currents in the whole-cell configuration. Compared to controls, significant differences in sodium-currents were observed after the application of NPs. Using the computational model, we could evaluate the parameters which model the change in behavior of neuronal cells due to the addition of Ag-Nano. This can ultimately give insight to underlying mechanisms. An integration to model the dynamic behavior of neuronal networks exposed to NP is easily conceivable using this technique.

Klinische und diagnostische Befunde bei Exposition gegenüber Nanopartikeln und neuen Materialien

Abstract: Innovative Technologien bedurfen einer adaquaten arbeitsmedizinischen Risikobewertung mit Ableitung geeigneter Arbeitsschutzmasnahmen. Dies ist auch fur die Nanotechnologie zu fordern.

Low cycle fatigue and creep–fatigue interaction in short fibre reinforced aluminium alloy composite

Abstract: The high temperature low cycle fatigue resistance and the creep–fatigue interaction (CFI) behaviour in terms of the effects of prior fatigue exposure on the subsequent creep behaviour are evaluated and reported for a short alumina fibre (Saffil) reinforced aluminium alloy (Al–12Si–CuMgNi) matrix composite at 623 K. The prior fatigue to study the CFI behaviour was imparted in the form of low cycle fatigue loading in a fully reversed, total strain controlled loading up to a quarter of fatigue life at a total strain amplitude of 0·006 (the plastic strain amplitude at half-life is 0·004), corresponding to a plastic strain energy per cycle value of 0·46 MJ m–3. Subsequently, isothermal tensile creep tests were conducted at 623 K to evaluate the minimum creep rate, rupture time and strain to failure as a function of applied creep stress. Also examined were the fracture features as well as the nature and extent of damage that occurs during low cycle fatigue and creep–fatigue loading. The results obtaine...

Verfahren zur Herstellung von feinstrukturierten Oberflächen

Abstract: Die Erfindung betrifft ein Verfahren zur Herstellung von feinstrukturierten Oberflachen insbesondere in Kunststoffen und ein Verfahren zur Herstellung von Matrizen zur Herstellung von feinstrukturierten Oberflachen.

Device having controllable adhesion

Abstract: A combination includes a first device and a second device, wherein both devices comprise at least one surface and the surface of the first device comprises at least one recess. At least one contact surface is formed when the surface of the first device attaches to the surface of the second device. By applying external pressure, the adhesion force between the two devices can be switched back and forth between at least two states.

Vorrichtung mit steuerbarer adhäsion

Abstract: Die Erfindung betrifft eine Kombination einer ersten Vorrichtung und einer zweiten Vorrichtung, wobei beide Vorrichtungen mindestens eine Oberflache aufweisen, und die Oberflache der ersten Vorrichtung mindestens eine Vertiefung aufweist; und sich bei Anlagerung der Oberflache der ersten Vorrichtung an die Oberflache der zweiten Vorrichtung mindestens eine Kontaktflache ausbildet. Durch das Anlegen von auserem Druck kann die Adhasionskraft zwischen den beiden Vorrichtungen zwischen mindestens zwei Zustanden hin- und her geschaltet werden.

Micropatterned Polymer Surfaces and Cellular Response of Dictyostelium

Abstract: Gecko inspired adhesives are surfaces with many microscale pillars that form Van der Waals forces with other surfaces. They differ from conventional tape in that adhesion is reversible and has the potential for switchability. These properties make gecko adhesives interesting for various biomedical applications. The two objectives of this project were to investigate the formation of biofilms on such surfaces and how the surfaces affect cell development. The developmental stages of the model organism Dictyostelium discoideum were observed by time lapse photography using light and environmental scanning electron microscopy. This study shows that micropatterned surfaces can be used as a biophysical tool to interfere with multicellular tissue formation in multiple ways.

Auf dem Weg in die industrielle Anwendung

Abstract: „Von der Natur lernen“ ist ein viel zitiertes Ziel moderner Materialforschung. Doch Nachahmen allein reicht nicht: Ein multidisziplinarer Ansatz, bestehend aus Biologie, Physik, Chemie, Materialwissenschaft und theoretischer Mechanik ist notwendig, um die in der Evolution erfolgreichen Prinzipien zu verstehen und auf technische Systeme zu ubertragen. So konnten neue Haftoberflachen entwickelt werden, fur die sich bereits ein groser industrieller Einsatzbedarf abzeichnet — vom Haushaltsartikel bis zum medizinischen Implantat.