Surface Friction Force Research Articles

활주로 고무 퇴적물 제거를 위한 포장 파손 저감형 사전처리제 개발 연구

항공기 착륙 시 발생하는 고무퇴적물은 젖은 노면에서의 표면 마찰력을 감소시키는 주원인으로 안전한 항공기 착륙을 위해 주기적인 제거를 실시하고 있다. 제거작업에 주로 사용되는 고압살수 방법은 고압의 물로 직접 표면을 타격함에 따라 표면 재료 유실의 원인이 되고 있다. 본 연구에서는 고무 제거시 살수 압을 상대적으로 낮추어 표면 파손을 저감시키고, 저수압에도 효율적으로 고무퇴적물을 제거할 수 있는 사전 처리제 개발을 진행하였다. 이를 위해 사전 처리제에 적합한 기초재료를 선정하여 성능 평가, 침투율 평가, 현장 적용성 평가를 진행하였다. 이를 토대로 기초재료의 성능 개선에 필요한 첨가제의 비율을 1차적으로 선정하였고, 포장 영향성 평가를 통해 최적배합을 도출하여 고무제거 사전처리제 개발을 완료하였다. Rubber deposited during aircraft landing is known as the main cause of reducing surface friction force on wet surfaces. Thus, rubber deposits are removed at regular intervals for sae airplane landing. The high-pressure waterblast method, widely used for the removal of rubber deposits, is regarded as the main cause for the loss of surface material because in this method, water hits the surface directly at a high pressure. In this study, a rubber removal primer is developed to reduce surface damage by lowering the pressure of waterblast relatively during the removal of rubber deposits such that the deposits are removed efficiently even with a lower water pressure. To achieve this, basic materials appropriate for the primer were selected and their performance, penetration rate, and site applicability were evaluated. Based on the evaluations, the proportion of additive required for improving the performance of the basic materials was first determined. Then, the optimum mix ratio was derived through the evaluation of the effect on pavements, and the development of the rubber removal primer was completed.

Influence of Alkali Ions on Tribological Properties of Silicon Surface

Tribological properties of surfaces (friction, adhesion and wear) provide challenging limitations to the design of reliable machines on the micro- and nanometer scale as the surface to volume area increases and volume, mass and inertia of the mobile parts decrease. This study reports on the reduction in the friction force of silicon surfaces after the alkali metal ion exposure in the form of aqueous solutions. A scanning force microscope equipped with a liquid cell was used to investigate the friction force and the pull-off force of a flat silicon surface immersed in water and in different alkali metal chlorides solutions: LiCl, NaCl and CsCl. The concentration ranged from 0.1 up to 1000 µmol/l. The changes in the free surface energy of the initial surface and of the modified surfaces after drying were determined from contact angle measurements and from the acid–base adhesion theory. In both cases, in the liquid environment and after drying of the exposed silicon substrates in air, the friction force is reduced by approximately 50 %. Our results provide new, fundamental insight into the exchange of surface termination layers in particular for tribology. Also it is suggested to use the procedure as a low-cost alternative to improve the tribological properties of the silicon surface in particular in applications where lubricating fluids are not appropriate, e.g., in nanomachines and devices.

Experimental and finite element studies of thin bonded and hybrid carbon fibre double lap joints used in aircraft structures

Finite element analysis (FEA) is performed to verify the static and fatigue strength of mechanically fastened, bonded and hybrid double lap joints. These joints are made from thin carbon fibre/epoxy laminates applied in aircraft structures. Several configurations are considered, including variations in rivet array and the addition of bondline defects. Adhesive nonlinear material properties, rivet surface contacts and frictional forces were included in the three-dimensional (3D) Finite Element (FE) models. The Multicontinuum Theory (MCT) is used to simulate the progressive failure process and the stress state for all specimens, whilst the strain energy release rate (SERR) as a function of crack length for bonded and hybrid specimens are also compared. Results have shown the FE models are able to accurately predict the bonded, riveted and hybrid joint strengths. The position of the first row of fasteners is critical in determining the crack growth rate. As the crack enters the fasteners' clamping zone there is a significant drop in SERR resulting in a much slower crack growth rate, therefore increasing the fatigue resistance of the hybrid joint configuration.

Preparation and nanotribological properties of polyelectrolyte multilayers with in situ Au nanoparticles

Abstract Polyelectrolyte multilayers with in situ Au nanoparticles were prepared by alternate immersion of a substrate in poly(allylamine hydrochloride) (PAH)-AuCl4− complexes solution and poly(acrylic acid) solution for layer-by-layer self assemble process followed by reduction of the metal cations Au3+ through immersion into a fresh NaBH4 solution. UV–vis spectrum, atomic force microscopy (AFM), X-ray photoelectron spectra (XPS), and transmission electron microscope (TEM) were used to confirm the construction of multilayers and synthesis of the Au nanoparticles. The nanotribological behaviors also have been studied using AFM. The polyelectrolyte multilayers with in situ Au nanoparticles exhibited a lower surface adhesion and friction force than the pure polyelectrolyte multilayers due to the nanoparticles improved the mutilayers surface structure and possess a good load-carrying capacity in nanoscale.

Comparison of photocatalytic activity and surface friction force variation on Ti-doped hydroxyapatite and anatase under UV illumination

Abstract Photocatalytic activity and surface friction variation were evaluated on Ti-doped hydroxyapatite (Ti-HAp) and anatase-type TiO 2 powders under UV illumination. Although the adsorption capability of Ti-HAp against gaseous 2-propanol (IPA) in the dark was greater than that of anatase, photocatalytic decomposition activity and water adsorption capability of Ti-HAp under UV illumination were inferior to those of anatase. Experiments using powder/epoxy composites revealed that Ti-HAp does not exhibit photocatalytic wettability conversion to a hydrophilic state, which was confirmed on anatase. The surface friction force variation of anatase under UV illumination was similar to previously reported trend for rutile ceramics. That of Ti-HAp exhibited a different trend against anatase, suggesting that its surface was originally more hydrophobic than anatase or cantilever.

THE FRICTION MECHANISM BETWEEN SURFACES WITH REGULAR MICRO GROOVES UNDER BOUNDARY LUBRICATION

The results of research related to the influence of partially regular microrelief parameters on the adhesion component of the friction factor under boundary lubrication are presented. It has been shown that micro grooves are effective under boundary friction on precision surfaces with low roughness when lack of film and probability of seizure appear. The deformation component of the friction force of surfaces with micro grooves has been studied. The time of micro running-in was the key factor while assessing the dependence of the deformation component on friction when taking into account the depth of micro grooves and their relative area. The research was conducted using a tribometer according to the friction model entitled “shaft & flexible steel tape”.

모발 개선을 위한 Transglutaminase의 적용

단백질을 연결시키는 효소인 transglutaminase는 모발에서 다양한 효과를 나타낼 수 있는 가능성이 있는데 이중에는 모발의 단단함을 증가시키는 작용도 포함된다. 여러 transglutaminase 효소 중 Streptomyces mobaraensis로부터 분리된 미생물 유래 효소를 손상된 모발에 사용한 후 인장강도를 평가한 결과 초기에 비해 15.64%까지 증가되는 것이 확인되었다. 이러한 효과는 transglutaminas가 샴푸를 사용하여 세정하는 과정에서의 모발 손상을 복구시킬 수 있다는 것을 의미한다. 또한 transglutaminase를 이용해 모발 표면의 특성을 개선 시킴으로써 모발의 윤기를 증가시키고 표면의 마찰력을 감소시키는데 유용하게 이용될 수 있었다. The use of protein-crosslinking enzyme, transglutaminase, as a biocatalyst in the processing of hair offers a variety of exciting and realistic possibilities which include improving the rigidity of hair fibers. Among the transglutaminases from many different living organisms, the microbial enzyme prepared from Streptomyces mobaraensis, significantly increased the tensile strength of hair by 15.64% compared to a control when it was applied to damaged hair. This indicates that transglutaminase can restore the negative effects of washing hair with shampoo. Also transglutaminase improved the characteristics of hair surface, which could be useful for increase of luster and reduction of friction force of hair surfaces.

Effect of ion-implantation on surface characteristics of nickel titanium and titanium molybdenum alloy arch wires

To evaluate the changes in surface roughness and frictional features of 'ion-implanted nickel titanium (NiTi) and titanium molybdenum alloy (TMA) arch wires' from its conventional types in an in-vitro laboratory set up. 'Ion-implanted NiTi and low friction TMA arch wires' were assessed for surface roughness with scanning electron microscopy (SEM) and 3 dimensional (3D) optical profilometry. Frictional forces were studied in a universal testing machine. Surface roughness of arch wires were determined as Root Mean Square (RMS) values in nanometers and Frictional Forces (FF) in grams. Mean values of RMS and FF were compared by Student's 't' test and one way analysis of variance (ANOVA). SEM images showed a smooth topography for ion-implanted versions. 3D optical profilometry demonstrated reduction of RMS values by 58.43% for ion-implanted NiTi (795.95 to 330.87 nm) and 48.90% for TMA groups (463.28 to 236.35 nm) from controls. Nonetheless, the corresponding decrease in FF was only 29.18% for NiTi and 22.04% for TMA, suggesting partial correction of surface roughness and disproportionate reduction in frictional forces with ion-implantation. Though the reductions were highly significant at P < 0.001, relations between surface roughness and frictional forces remained non conclusive even after ion-implantation. The study proved that ion-implantation can significantly reduce the surface roughness of NiTi and TMA wires but could not make a similar reduction in frictional forces. This can be attributed to the inherent differences in stiffness and surface reactivity of NiTi and TMA wires when used in combination with stainless steel brackets, which needs further investigations.

Friction and Wear of Porcine Articular Joint and Effects of Selective Digestions

In this work, we explored the possible existence of a wear mechanism developing under mild conditions using surface force apparatus (SFA). By selectively digesting different components (type II collagen, Hyaluronic acid (HA), glycosaminoglycans (GAGs)) of the cartilage, we also establish correlation between the structural properties of cartilage surface and the tribological properties.We observed stick-slip friction in articular cartilage for the first time under mild conditions. To visualize load and speed regimes of stick-slip friction occurrence we introduced ‘Dynamic (friction) phase diagram'. Prolonged exposure of the cartilage surfaces to stick-slip sliding results in an increase of surface roughness similar to HA and GAGs digested cartilage suggesting that stick-slip motion is able to induce severe morphological changes of cartilage superficial zone. We also found that digestion of the different components of cartilage alters the morphology of the superficial zone in very different ways. HA and GAGs digestions increased surface roughness while collagen digestion decreased the surface roughness compared to normal cartilage. Friction forces increased up to 2, 5 and 10 times after HA, collagen and GAGs digestion, respectively, indicating no direct correlation between surface roughness and friction forces.

Nanostructures and surface nanomechanical properties of polyacrylonitrile/graphene oxide composite nanofibers by electrospinning

AbstractIn this work, polyacrylonitrile (PAN)/graphene oxide (GO) composite nanofibers were prepared by a facile compounding and electrospinning processes. A small amount of GO powders were first dispersed in N,N‐dimethylformamide by sonication, and then, PAN powders were added to prepare an electrospinning solution. The surface morphology was analyzed by atomic force microscopy and transmission electron microscopy, whereas the chemical properties of the PAN and PAN/GO composite nanofibers were compared by infrared (IR) spectroscopy. Also, lateral force microscopy and force–distance curves (FDC) were employed to investigate the surface properties, such as friction force and elasticity. The experimental results indicate that with increasing GO concentration, the surface friction force and adhesive force increased, so the nanofibers showed promise for applications as supports for enzyme immobilization. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Enhancement of polylactide nucleation by montmorillonites intercalated with a green seaweed byproduct

AbstractPolylactide (PLA) nanocomposites with improved mechanical and barrier properties are of growing industrial interest and therefore required green modified montmorillonites (gm‐MMTs) to meet the expectation of totally biosourced material. In this study, ulvans that are polysaccharides and glycoproteins extracted from seaweed are used as surfactants to achieve intercalated clays. The effect of this gm‐MMT (ALL350) on the crystallization kinetics of PLA was compared to Cloisite 30B, and pristine MMT was taken as a reference. Rheology, differential scanning calorimetry, and transmission electronic microscopy experiments were performed to better understand the effects that dominate the so‐called nucleating effect observed in PLA nanocomposites. It was found that two major driving forces explain the efficiency of the ALL350 that enhances PLA nucleation. The first one is the decrease of the interfacial energy and the second is a reduction of the complex viscosity that acts on the induction period. Reduction of both the interfacial energy and the surface friction forces between PLA chains and polysaccharides‐treated clay platelets is assumed to facilitate the induction process. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effect of Cavitation on Tribological Performances for Textured Surfaces

The influence of cavitation in a lubricant between textured surfaces on tribological performances of the surfaces was investigated based on an extended Reynolds equation and other associated equations. The tribological performances of the surfaces holding dimples with divergent-convergent shape were analyzed with the cavitation effect consideration at different dimple numbers. In doing so, the elastic deformation of the surface is evaluated using continuous convolution fast Fourier transform (CC-FFT). Some mechanisms are revealed about the cavitation effect on the friction coefficient, friction force, load-carrying capacity and cavitated area of the textured surfaces.

Surface and friction forces between grafted polysaccharide layers in the absence and presence of surfactant

We analyzed the interaction between chemically grafted polysaccharide layers in aqueous solutions. To fabricate such layers, an end-terminated dextran silane coupling agent was synthesized and the polydextran was grafted to oxidized silicon wafers and to silica particles. This resulted in the formation of a 28nm thick layer (in air) and a grafted amount of 40mg/m2 as determined by ellipsometry. The physical properties of the grafted layer were investigated in aqueous solutions by atomic force microscope imaging and colloidal probe force measurements. Surface and friction forces were measured between one bare and one polydextran coated silica surface. A notable feature was a bridging attraction due to affinity between dextran and the silica surface. Surface interactions and friction forces were also investigated between two surfaces coated with grafted polydextran. Repulsive forces were predominant, but nevertheless a high friction force was observed. The repulsive forces were enhanced by addition of sodium dodecyl sulfate (SDS) that associates with the tethered polydextran layers. SDS also decreased the friction force. Our data suggests that energy dissipation due to shear-induced structural changes within the grafted layer is of prime importance for the high friction forces observed, in particular deformation of protrusions in the surface layer.

Annealing improves tribological property of poly(octadecene-alt-maleic anhydride) self-assembled film

A poly(octadecene-alt-maleic anhydride) (POMA) film was covalently immobilized on N-[3-(trimethoxylsilyl)propyl]ethylenediamine self-assembled monolayer modified silicon surface. Attenuated total reflectance Fourier transform infrared spectra were used to confirm the chemical bonding. Water contact angles and ellipsometric thicknesses were measured before and after annealing treatment. Atomic force microscopy was applied for top morphology, surface adhesion force and friction force. Anti-wear properties of the films were also evaluated on a ball-on-plate tribometer. It was found that annealing treatment which would evoke a conformation transform thermodynamically, was a critical step in the preparation of anti-wear films, especially for polymer ones. The correlation between structure and tribological property was revealed, which has profound meaning in designing excellent anti-wear nano-coatings used in microelectronic mechanical systems (MEMS).

Scratch direction and threshold force in nanoscale scratching using atomic force microscopes

The nanoscaled tip in an AFM (atomic force microscope) has become an effective scratching tool for material removing in nanofabrication. In this article, the characteristics of using a diamond-coated pyramidal tip to scratch Ni–Fe thin film surfaces was experimentally investigated with the focus on the evaluation of the influence of the scratch or scan direction on the final shape of the scratched geometry as well as the applied scratch force. Results indicated that both the scratched profile and the scratch force were greatly affected by the scratch direction. It has been found that, to minimize the formation of protuberances along the groove sides and to have a better control of the scratched geometry, the tip face should be perpendicular to the scratching direction, which is also known as orthogonal cutting condition. To demonstrate the present findings, three groove patterns have been scratched with the tip face perpendicular to the scratching direction and very little amount of protuberances was observed. The threshold scratch force was also predicted based on the Hertz contact theory. Without considering the surface friction and adhesive forces between the tip and substrate, the threshold force predicted was twice smaller than the measurement value. Finally, recommendations for technical improvement and research focuses are provided.

Wettability conversion and surface friction force variation of polycrystalline rutile ceramics under UV illumination

Photoinduced surface friction variations of the polished surface of polycrystalline rutile ceramics under UV illumination in different atmospheres was evaluated using FFM. When UV was irradiated onto the rutile surface, the surface friction force first increased and then decreased. Once the water contact angle of the rutile surface reached the lower limit, the surface friction force increased gradually. Increased friction force on the surface in the early stage of UV illumination was attributable to decomposition of the surface organic contaminant and the resultant increase of surface energy from the fitting of calculated contact angles to practical values. However, the friction force decrease and gradual increase after a certain period of UV illumination are attributed to the lubrication effect and either a capillary effect or the increased adsorbed water layer by humidity control. From the force curve measurement on the highly hydrophilic rutile single crystal (1 0 0), the repulsion force was detected from 2 to 3 nm separation distance.

Frictional properties of VA‐mode alignment‐film surfaces studied by frictional force microscopy

Abstract— The surface‐friction characteristics of the post‐bake temperature were compared to that of the rubbing condition on VA‐mode alignment films (AFs) using frictional force microscopy (FFM). The surface roughness and the surface frictional force increased when the temperature was elevated. However, the frictional asymmetry could not be detected by the frictional loop due to the instability of the side‐chain molecular arrangement. For the inter‐influences of the total friction and surface roughness, the density of the side chain was changed and it was intentionally rubbed for evaluation. The results showed that the total friction was higher when the rubbing was stronger and side‐chain density lower, and the surface roughness also increased in the same manner. This can be explained by the potential interaction due to the curved structure of the side‐chain surface that establishes the probe that is scanned and the top surface layer. In order to confirm the influence of the pre‐tilt angle on the tilt of the side chain, a test cell was produced under the same conditions and evaluated. The results showed that the pre‐tilt‐angle decreased according to the difference in density of the side chain and strength of rubbing after injecting liquid‐crystal (LC).

AFM surface morphology and friction force studies of microscale domain structures of binary phospholipids

We have studied friction forces on binary mixtures of phospholipid monolayer films. The phospholipid monolayer films have been prepared via the Langmuir–Blodgett (LB) technique on mica. The two-component phospholipids are distearoylphosphatidylcholine (DSPC) and dilauroylphosphatidylcholine (DLPC). At 25 °C the LB monolayer films give the gel-state DSPC domains surrounded by the liquid crystalline DLPC matrix. The friction forces measured on the DSPC domain region are significantly greater than those on the DLPC matrix region at this temperature. An increased temperature results in a decreased friction of the DSPC domain region, and above the gel-to-liquid crystalline phase transition temperature of DSPC, the difference in the friction forces measured on the two phospholipids becomes negligible. This means that the phase state is a key factor in determining friction forces on the phospholipid monolayer films.

Lubrication by organized soft matter

The AFM-colloidal probe technique has been used to explore surface interactions and friction forces between polyelectrolyte-coated surfaces immersed in aqueous solutions in the absence and presence ...

Surface analysis and frictional force measurement of the shear surface at the residual state of clay by AFM.

In this research paper the residual strength of clay is deemed to correspond to the total value of the strength of the soil particles used in the specimen. The frictional force of the soil particles was measured by using Atomic Force Microscope (AFM); then the frictional force and the residual strength of the specimen were compared. The surface profile of the shear surface in residual state, the friction coefficient, the velocity de­ pendency of frictional force and the adsorptive force of clay adsorbed water were measured by AFM in micro area. As a result, although the shear surface appeared flat to the naked eye, it actually turned out to be rough. The increase of the frictional force in micro area was proportional to the increase in the vertical stress, and the increase rate or angle of friction [ <p] was very small: less than 5°. The adsorptive force of adsorbed water was 4.1 X 1 o2 nN for Kunipia F, 8.9 X 1 o-I nN for Kaolin KH from the Force Curve. Since the angle of shear re­ sistance of the specimen in macro [<p',] was around 20°, the shear strength of macro and micro were not equal. Even when the micro strength was simply integrated, it didn't equal the macro strength.