Exploring wear at the nanoscale with circular mode atomic force microscopy

• Olivier Noel,
• Aleksandar Vencl and
• Pierre-Emmanuel Mazeran

Beilstein J. Nanotechnol. 2017, 8, 2662–2668, doi:10.3762/bjnano.8.266

• . Consequently, the shear stress applied to the contact appears to be not high enough to wear the material. The wear depths determined from the wear profiles (Figure 3D for example) are in the nanometer range. One can calculate from Figure 5 in the steady-state regime for an applied load of 3 µN that about 100

Numerical investigation of the tribological performance of micro-dimple textured surfaces under hydrodynamic lubrication

• Kangmei Li,
• Dalei Jing,
• Jun Hu,
• Xiaohong Ding and
• Zhenqiang Yao

Beilstein J. Nanotechnol. 2017, 8, 2324–2338, doi:10.3762/bjnano.8.232

• wall of the calculation domain, that is, the area of the micro-dimple unit. A high dimensionless average film carrying force indicates a good load-carrying capacity of the friction pair. In a similar way, as shown in Equation 9, the film shear force is calculated by integrating the shear stress along

• the y-axis on the upper wall over the total calculation domain: where Fy is shear force and τ′ is the shear stress. The dimensionless form of the average film shear force can be obtained by The friction coefficient is defined as the ratio of the dimensionless average film shear force to the

Stick–slip boundary friction mode as a second-order phase transition with an inhomogeneous distribution of elastic stress in the contact area

• Iakov A. Lyashenko,
• Vadym N. Borysiuk and
• Valentin L. Popov

Beilstein J. Nanotechnol. 2017, 8, 1889–1896, doi:10.3762/bjnano.8.189

• of the friction block through an elastic spring, the frequency of the melting/solidification phase transitions increases with time. Keywords: boundary friction; dimensionality reduction; numerical simulation; shear stress and strain; stick–slip motion; tribology; Introduction The boundary friction

• radial coordinate r: Knowing the distribution of strain ε(r) and order parameter φ(r) we can obtain the distribution of the stress in the lubricant according to Equation 2: The distribution of the displacements in Equation 11 is defined by shear stress. In our further investigations we will use the

Studying friction while playing the violin: exploring the stick–slip phenomenon

• Santiago Casado

Beilstein J. Nanotechnol. 2017, 8, 159–166, doi:10.3762/bjnano.8.16

• effect originates from the periodic rupture of junctions created between two rubbing surfaces due to the increasing shear stress at the interface. It is ultimately responsible for the behavior of many braking systems, earthquakes, and unpleasant squeaky sounds caused by the scratching of two surfaces. In

Structural and tribometric characterization of biomimetically inspired synthetic "insect adhesives"

• Matthias W. Speidel,
• Malte Kleemeier,
• Andreas Hartwig,
• Klaus Rischka,
• Angelika Ellermann,
• Rolf Daniels and
• Oliver Betz

Beilstein J. Nanotechnol. 2017, 8, 45–63, doi:10.3762/bjnano.8.6

• adhesive fluid-mediated insect locomotion, attachment forces are largely determined by the viscosity of the fluid, because of its influence on the shear stress generated during friction. High viscosity fluids should therefore be avoided during locomotion, because this would be counterproductive for the

• detachment process. In our experiments, in order to ensure that the shear stress of the bulk emulsions was assessed in a hydrostatic or hydrodynamic sliding regime (preventing solid–solid contact between the sliding surfaces or solidification processes that might occur in confined liquids), the load employed

• relatively high adhesiveness, the two presumed water-in-oil (w/o) emulsions SA4 and SG4 of the second generation exhibited similarly low shear stresses. Such behaviour (low shear stress at relatively high

Graphene–polymer coating for the realization of strain sensors

• Carmela Bonavolontà,
• Carla Aramo,
• Massimo Valentino,
• Giampiero Pepe,
• Sergio De Nicola,
• Gianfranco Carotenuto,
• Angela Longo,
• Mariano Palomba,
• Simone Boccardi and
• Carosena Meola

Beilstein J. Nanotechnol. 2017, 8, 21–27, doi:10.3762/bjnano.8.3

• poly(methyl methacrylate) (PMMA). The good adhesion to the PMMA surface, combined with the shear stress, allows a uniform and continuous spreading of the graphite nanocrystals, resulting in a very uniform graphene multilayer coating on the substrate surface. The fabrication process is simple and yields

• surface, combined with the shear stress, allowed for the uniform and continuous spreading of the graphite nanocrystals on the substrate surface with formation of a very uniform graphene multilayer coating. The electrical response to the mechanical deformation of a strain sensor is generally quantified by

• ) film to achieve a very uniform coating of the substrate surface. The adhesion to the PMMA surface, combined with the applied shear stress, allowed a uniform and continuous spreading of the graphite nanocrystals on the substrate surface with formation of a very uniform graphene multilayer coating. The

When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs

• Niall Crawford,
• Thomas Endlein,
• Jonathan T. Pham,
• Mathis Riehle and
• W. Jon P. Barnes

Beilstein J. Nanotechnol. 2016, 7, 2116–2131, doi:10.3762/bjnano.7.201

• frictional shear stress (Figure 2A). Forces initially increased with roughness, with the largest shear stresses being measured on the 6 µm surface (30.1 ± 13.8 kPa; z = −5.1672, p < 0.00014). Shear stress values on the 15 µm surfaces were 18.48 ± 6.1 kPa, higher than the smooth values (z = −5.5663, p

• < 0.00014), but lower than the forces on the 6 µm surface. The shear stress measured on the largest roughnesses tested were at a consistent level of ca. 16 kPa, still higher than those measured on the smooth surface (e.g., comparing smooth to 100 µm, z = −5.5072, p < 0.00014). Adhesive forces (Figure 2B

• variation of rough surfaces made from PDMS were tested, where the only parameter changed between surfaces is the gap between the asperities on the surface. Force per unit area measurements on these rough surfaces were compared to forces measured on a smooth PDMS surface (Figure 3). Shear stress values (n

A new approach to grain boundary engineering for nanocrystalline materials

• Shigeaki Kobayashi,
• Sadahiro Tsurekawa and
• Tadao Watanabe

Beilstein J. Nanotechnol. 2016, 7, 1829–1849, doi:10.3762/bjnano.7.176

• probably deformed by shear stress as in the case of a single crystal, because the persistent slip bands (PSBs) can continuously transfer across the low-angle boundaries [97]. The fatigue cracks preferentially nucleated along random boundaries whose boundary plane may almost correspond to the direction of

The self-similarity theory of high pressure torsion

• Yan Beygelzimer,
• Roman Kulagin,
• Laszlo S. Toth and
• Yulia Ivanisenko

Beilstein J. Nanotechnol. 2016, 7, 1267–1277, doi:10.3762/bjnano.7.117

• self-similar solution, according to which the following relations hold for the velocity vector for the strain rate tensor the von Mises strain and the shear stress where the exponent n is equal to the exponent in the hardening law of the material, while the function u = u(r,z) is the solution of

• ). Finally, for shear stress and torque, the exponent is equal to the exponent of the hardening law (see Equation 39 and Equation 40). The second-order differential Equation 32 cannot be solved analytically. Therefore, numerical simulations are needed to identify self-similar solutions. In this section, we

• angles (henceforth, scaling range), the HPT parameters are proportional to (β/β0)q, where β0 is an arbitrary angle that belongs to the scaling range (e.g., its median), q = 0 for velocity and strain rate, q = 1 for shear strain and for von Mises strain, q = n for shear stress and torque (where n is the

Tight junction between endothelial cells: the interaction between nanoparticles and blood vessels

• Yue Zhang and
• Wan-Xi Yang

Beilstein J. Nanotechnol. 2016, 7, 675–684, doi:10.3762/bjnano.7.60

• blood vessels, which are the sites of phosphorylation of tight junction proteins (claudins, occludins, and ZO (Zonula occludens)) proteins, oxidative stress and shear stress. We propose a connection between the presence of nanoparticles and the regulation of the tight junction, which might be the key

• : (1) phosphorylation, (2) expression level of occludins and (3) shear stress. Research about the phosphorylation of occludins in rat brain capillaries after embolism showed that an increased level of tyrosine phosphorylation in occludins might play an important role regarding the disruption of the

• bile duct ligation researchers suggested a relationship between the time-dependent down-regulation of the occludin expression and a time-dependent increase of superoxide radical levels in the brain [68]. Another factor, shear stress, different from normal stressors, exerts a perpendicular force on the

Stiffness of sphere–plate contacts at MHz frequencies: dependence on normal load, oscillation amplitude, and ambient medium

• Jana Vlachová,
• Rebekka König and
• Diethelm Johannsmann

Beilstein J. Nanotechnol. 2015, 6, 845–856, doi:10.3762/bjnano.6.87

• can be explained by nanoroughness. In other words, contact splitting (i.e., a transport of shear stress across many small contacts, rather than a few large ones) can be exploited to reduce partial slip. Keywords: contact mechanics; contact splitting; contact stiffness; partial slip; quartz crystal

Entropy effects in the collective dynamic behavior of alkyl monolayers tethered to Si(111)

• Christian Godet

Beilstein J. Nanotechnol. 2015, 6, 583–594, doi:10.3762/bjnano.6.60

• insulating OML with thickness dOML and dielectric permittivity εI: This electrostatic force leads to compressive and shear stress components, respectively, normal and parallel to the substrate. Furthermore, each molecule is considered as a rigid elastic rod, tilted at some angle with respect to the normal to

• molecular monolayer is described by a normal compressive load. Bottom: the mechanical response to the induced shear stress may lead to global chain axis tilting (left panel) or formation of gauche defects preferentially localized at chain ends (right panel). Imaginary electrical modulus M″(ω) of the Hg/acid

A surface acoustic wave-driven micropump for particle uptake investigation under physiological flow conditions in very small volumes

• Florian G. Strobl,
• Dominik Breyer,
• Phillip Link,
• Adriano A. Torrano,
• Christoph Bräuchle,
• Matthias F. Schneider and
• Achim Wixforth

Beilstein J. Nanotechnol. 2015, 6, 414–419, doi:10.3762/bjnano.6.41

• surrounding for these cells, which are exposed in vivo to shear rates of up to 3000 s−1 [6]. It was recently shown that the glycocalix of endothelial cells is substantially reorganized under shear [7] and several effects of shear stress on cellular uptake mechanisms have been reported [8][9][10]. One solution

• . The chip is mounted onto a culture slide by a metal frame. b) Sketch of the chip. A focusing interdigital transducer induces acoustic streaming with the main flow component pointing downwards, incident at the bottom in an angle of approximately 23° and inducing shear stress on the surface. c

On the structure of grain/interphase boundaries and interfaces

• K. Anantha Padmanabhan and
• Herbert Gleiter

Beilstein J. Nanotechnol. 2014, 5, 1603–1615, doi:10.3762/bjnano.5.172

Surface topography and contact mechanics of dry and wet human skin

• Alexander E. Kovalev,
• Kirstin Dening,
• Bo N. J. Persson and
• Stanislav N. Gorb

Beilstein J. Nanotechnol. 2014, 5, 1341–1348, doi:10.3762/bjnano.5.147

• skin. The measured friction coefficient between a glass ball and dry and wet skin can be explained assuming that a frictional shear stress σf ≈ 13 MPa and σf ≈ 5 MPa, respectively, act in the area of real contact during sliding. These frictional shear stresses are typical for sliding on surfaces of

• sliding on different surfaces [19], during which for sliding velocities of the order of cm/s the frictional shear stress is typically of the order of 2–8 MPa. Capillary adhesion In this section we evaluate different factors determining the tribological behaviour of wet skin, which is described in [3

• be explained assuming that a frictional shear stress σf ≈ 10 MPa acts in the area of real contact during sliding. This frictional shear stress is typical for sliding on elastomeric surfaces, and for nanometer thick confined fluid films. The big increase in friction, which has been observed for glass

Physical principles of fluid-mediated insect attachment - Shouldn’t insects slip?

• Jan-Henning Dirks

Beilstein J. Nanotechnol. 2014, 5, 1160–1166, doi:10.3762/bjnano.5.127

• mm2 [16], the maximal possible shear stress before sliding occurs (with cos α1 − cos α2 ≤ 2) would be only approx. 0.38 kPa. This value (and the corresponding value for smaller contact areas) is several orders of magnitude smaller than the shear stresses measured in smooth adhesive pads of the stick

Manipulation of nanoparticles of different shapes inside a scanning electron microscope

• Boris Polyakov,
• Sergei Vlassov,
• Leonid M. Dorogin,
• Jelena Butikova,
• Mikk Antsov,
• Sven Oras,
• Rünno Lõhmus and
• Ilmar Kink

Beilstein J. Nanotechnol. 2014, 5, 133–140, doi:10.3762/bjnano.5.13

• calculated the friction force values, Ffriction, by using a simple relation: where τ is the interfacial shear stress/strength and A is the contact area [26]. The shear strength is defined as an ultimate shear stress τ before the object is displaced, and can be estimated by using the relation τtheo = G*/Z

• between the theoretical shear strength and the combined shear modulus, where ν is the Poisson ratio and G1,2 = E1,2/2(1 + ν1,2) [27][28]. Z is an empirical coefficient that depends on the material and ranges from 5 to 30 [29]. To calculate interfacial shear stress/strength τ for Au NPs the following

Static analysis of rectangular nanoplates using trigonometric shear deformation theory based on nonlocal elasticity theory

• Mohammad Rahim Nami and
• Maziar Janghorban

Beilstein J. Nanotechnol. 2013, 4, 968–973, doi:10.3762/bjnano.4.109

• shear correction factors unnecessary. Thai and Vo [11] proposed a new sinusoidal shear deformation theory for bending, buckling, and vibration of functionally graded plates. The theory accounted for sinusoidal distribution of transverse shear stress. Unlike the conventional sinusoidal shear deformation

Deformation-induced grain growth and twinning in nanocrystalline palladium thin films

• Aaron Kobler,
• Jochen Lohmiller,
• Jonathan Schäfer,
• Michael Kerber,
• Anna Castrup,
• Ankush Kashiwar,
• Patric A. Gruber,
• Karsten Albe,
• Horst Hahn and
• Christian Kübel

Beilstein J. Nanotechnol. 2013, 4, 554–566, doi:10.3762/bjnano.4.64

• Schmid-factor (the highest resolved shear stress). Here, randomly oriented twin boundaries can act as barriers to dislocation motion. In nano-twinned Pd, however, partial dislocations nucleate preferentially at twin boundaries. The twin boundaries then act as nucleation site and do not hinder successive

Plasticity of Cu nanoparticles: Dislocation-dendrite-induced strain hardening and a limit for displacive plasticity

• Antti Tolvanen and
• Karsten Albe

Beilstein J. Nanotechnol. 2013, 4, 173–179, doi:10.3762/bjnano.4.17

• cannot capture even the qualitative differences of the observed modes of plasticity. The only apparent difference, in addition to the hydrostatic pressure, is the initial stress distribution as seen in Figure 2d. At the lower orifice radii the shear stress is localised at the particle surface, and thus

Conducting composite materials from the biopolymer kappa-carrageenan and carbon nanotubes

• Ali Aldalbahi,
• Jin Chu,
• Peter Feng and
• Marc in het Panhuis

Beilstein J. Nanotechnol. 2012, 3, 415–427, doi:10.3762/bjnano.3.48

• around 0.5% w/v, which is characteristic of dilute to semidilute transition. The relation between shear stress and shear rate for IC solutions at different concentrations is shown in Figure 1b. It can be seen that KC solutions exhibit a yield point, i.e., the viscous KC solutions start to flow only when

• rheometer (Anton Paar–Physica MCR 301) with a 50 mm diameter probe head (cone angle 1°) at 21 °C. KC–CNT dispersions and KC solutions were analysed by using flow curves (viscosity and shear stress versus shear rate). The dynamic modulus was measured by using oscillatory strain sweeps at constant frequency

• that the change of gas concentration was instantaneous, which is a prerequisite condition for the accurate measurements of response and recovery time of the sensor. Effect of increasing concentration on (a) the viscosity and (b) the shear stress versus shear rate of KC solutions. The lines in (a) and

Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

• Bharat Bhushan

Beilstein J. Nanotechnol. 2011, 2, 66–84, doi:10.3762/bjnano.2.9

• and hierarchical structure. Bechert et al. [19] showed that a turbulent boundary layer on the shark skin surface with ribs can help to reduce turbulent shear stress (also see Dean and Bhushan [22]). The results of experimental measurements on shark skin replica showed that a reduction of pressure drop

• generally known that surfaces with a streamlined body can produce dramatic reductions of the fluid pressure drag with only a slight increase in shear stress in air flow [60]. It is also known that as the Reynolds number increases, the pressure drop becomes very large, resulting in larger pressure drag. The