scholarly journals PHASE DYNAMICS AND KINETICS OF THIN LUBRICANT FILM DRIVEN BY CORRELATED TEMPERATURE FLUCTUATIONS

2007 ◽  
Vol 07 (02) ◽  
pp. L111-L133 ◽  
Author(s):  
ALEXEI V. KHOMENKO ◽  
IAKOV A. LYASHENKO
Keyword(s):  
Sliding Friction ◽  
Temperature Fluctuations ◽  
Lubricant Film ◽  
Stick Slip ◽  
Flat Surfaces ◽  
Phase Dynamics ◽  
Damped Oscillations ◽  
Atomically Flat ◽  
Kinetics Of ◽  
Stable Sliding

The melting of an ultrathin lubricant film is studied at friction between atomically flat surfaces. We take into account fluctuations of lubricant temperature, which are defined by the Ornstein-Uhlenbeck process. Phase diagrams and portraits are calculated for second- and first-order transitions (the melting of an amorphous and that of a crystalline lubricants, respectively). It is shown that, in the former case, a stick-slip friction domain, separating the regions of dry and sliding friction, appears. In the latter case, three domains of stick-slip friction arise, which are characterized by the transitions between dry, metastable and stable sliding friction. The increase in the correlation time of lubricant temperature fluctuations leads to increasing in the rubbing-surface temperature needed for realization of sliding friction. The stationary states, corresponding to dry, stable and metastable sliding friction, are reached as a result of damped oscillations.

scholarly journals Squeezing and stick–slip friction behaviors of lubricants in boundary lubrication

2018 ◽  
Vol 115 (26) ◽  
pp. 6560-6565 ◽  
Author(s):  
Rong-Guang Xu ◽  
Yongsheng Leng
Keyword(s):  
Phase Transition ◽  
Boundary Lubrication ◽  
Sliding Friction ◽  
Surface Force ◽  
Lubricant Film ◽  
Force Balance ◽  
Surface Boundary ◽  
Stick Slip ◽  
Squeeze Out ◽  
Dynamics Simulations

The fundamental questions of how lubricant molecules organize into a layered structure under nanometers confinement and what is the interplay between layering and friction are still not well answered in the field of nanotribology. While the phase transition of lubricants during a squeeze-out process under compression is a long-standing controversial debate (i.e., liquid-like to solid-like phase transition versus amorphous glass-like transition), recent different interpretations to the stick–slip friction of lubricants in boundary lubrication present new challenges in this field. We carry out molecular dynamics simulations of a model lubricant film (cyclohexane) confined between molecularly smooth surfaces (mica)––a prototypical model system studied in surface force apparatus or surface force balance experiments. Through fully atomistic simulations, we find that repulsive force between two solid surfaces starts at about seven lubricant layers (n= 7) and the lubricant film undergoes a sudden liquid-like to solid-like phase transition atn< 6 monolayers thickness. Shear of solidified lubricant films at three- or four-monolayer thickness results in stick–slip friction. The sliding friction simulation shows that instead of shear melting of the film during the slip of the surface, boundary slips at solid–lubricant interfaces happen, while the solidified structure of the lubricant film is well maintained during repeated stick–slip friction cycles. Moreover, no dilation of the lubricant film during the slip is observed, which is surprisingly consistent with recent surface force balance experimental measurements.

scholarly journals Statistics of Sliding on Periodic and Atomically Flat Surfaces

2021 ◽  
Vol 7 ◽  
Author(s):  
Maja Srbulovic ◽  
Konstantinos Gkagkas ◽  
Carsten Gachot ◽  
András Vernes
Keyword(s):  
Equations Of Motion ◽  
Two Dimensions ◽  
Analytical Models ◽  
Fourier Series Expansion ◽  
Stick Slip ◽  
Time Resolved ◽  
Flat Surfaces ◽  
Atomic Force ◽  
Reaction Forces ◽  
Atomically Flat

Among the so-called analytical models of friction, the most popular and widely used one, the Prandtl-Tomlinson model in one and two dimensions is considered here to numerically describe the sliding of the tip within an atomic force microscope over a periodic and atomically flat surface. Because in these PT-models, the Newtonian equations of motion for the AFM-tip are Langevin-type coupled stochastic differential equations the resulting friction and reaction forces must be statistically correctly determined and interpreted. For this, it is firstly shown that the friction and reaction forces as averages of the time-resolved ones over the sliding part, are normally (Gaussian) distributed. Then based on this, an efficient numerical scheme is developed and implemented to accurately estimate the means and standard deviations of friction and reaction forces without performing too many repetitions for the same sliding experiments. The used corrugation potential is the simplest one obtained from the Fourier series expansion of the two-dimensional (2D) periodic potential, e.g., for an fcc(111) surface, which permits sliding on both commensurate and incommensurate paths. In this manner, it is proven that the PT-models predict both frictional regimes, namely the structural superlubricity and stick-slip along (in)commensurate sliding paths, if the ratio of mean corrugation and elastic energies is properly set.

scholarly journals MULTIFRACTAL ANALYSIS OF STRESS TIME SERIES DURING ULTRATHIN LUBRICANT FILM MELTING

2010 ◽  
Vol 09 (01) ◽  
pp. 19-35 ◽  
Author(s):  
ALEXEI V. KHOMENKO ◽  
IAKOV A. LYASHENKO ◽  
VADIM N. BORISYUK
Keyword(s):  
Time Series ◽  
Power Law ◽  
Lubricant Film ◽  
Fluctuation Analysis ◽  
Power Law Distribution ◽  
Stick Slip ◽  
Multifractal Detrended Fluctuation Analysis ◽  
Flat Surfaces ◽  
Self Similar ◽  
Detrended Fluctuation

Melting of an ultrathin lubricant film confined between two atomically flat surfaces is studied using the rheological model for viscoelastic matter approximation. Phase diagram with domains, corresponding to sliding, dry, and two types of stick-slip friction regimes has been built taking into account additive noises of stress, strain, and temperature of the lubricant. The stress time series have been obtained for all regimes of friction using the Stratonovich interpretation. It has been shown that self-similar regime of lubricant melting is observed when intensity of temperature noise is much larger than intensities of strain and stress noises. This regime is defined by homogenous distribution, at which characteristic stress scale is absent. We study stress time series obtained for all friction regimes using multifractal detrended fluctuation analysis. It has been shown that multifractality of these series is caused by different correlations that are present in the system and also by a power-law distribution. Since the power-law distribution is related to small stresses, this case corresponds to self-similar solid-like lubricant.

Self-Organized Criticality in Nanotribology

2003 ◽  
Vol 782 ◽  
Author(s):  
Micha Adler ◽  
John Ferrante ◽  
Alan Schilowitz ◽  
Dalia Yablon ◽  
Fredy Zypman
Keyword(s):  
Dry Friction ◽  
Sliding Friction ◽  
Stick Slip ◽  
Slip Mechanism ◽  
Flat Surfaces ◽  
Self Organized ◽  
Atomic Force ◽  
Lateral Forces ◽  
Self Organized Criticality ◽  
Sliding Distance

ABSTRACTWe present experimental results on dry friction, which are consistent with the hypothesis that the stick-slip mechanism for energy release is described by self-organized criticality. The data, obtained with an Atomic Force Microscope set to measure lateral forces– examines the variation of the friction force as a function of time – or sliding distance. The materials studied were nominally flat surfaces of mica, quartz, silica and steel. An analysis of the data shows that the probability distribution of slip sizes follows a power law. Our data strongly supports the existence of self-organized criticality for nano-stick-slip in dry sliding friction.

Quasi-Barrierless Submolecular Motion in Mechanically Interlocked Carbon Nanotubes

2020 ◽  
Author(s):  
Julia Villalva ◽  
Belén Nieto-Ortega ◽  
Manuel Melle-Franco ◽  
Emilio Pérez
Keyword(s):  
Density Functional ◽  
Close Contact ◽  
Tight Binding ◽  
Energetic Cost ◽  
Molecular Fragments ◽  
Activation Barriers ◽  
Flat Surfaces ◽  
Different Types ◽  
Atomically Flat ◽  
Derivatives Of

The motion of molecular fragments in close contact with atomically flat surfaces is still not fully understood. Does a more favourable interaction imply a larger barrier towards motion even if there are no obvious minima? Here, we use mechanically interlocked rotaxane-type derivatives of SWNTs (MINTs) featuring four different types of macrocycles with significantly different affinities for the SWNT thread as models to study this problem. Using molecular dynamics, we find that there is no direct correlation between the interaction energy of the macrocycle with the SWNT and its ability to move along or around it. Density functional tight-binding calculations reveal small (<2.5 Kcal·mol-1) activation barriers, the height of which correlates with the commensurability of the aromatic moieties in the macrocycle with the SWNT. Our results show that macrocycles in MINTs rotate and translate freely around and along SWNTs at room temperature, with an energetic cost lower than the rotation around the C−C bond in ethane.<br>

Influence of Momentary Annealing on the Nanoscale Surface Morphology of Room Temperature Pulsed Laser Deposited NiO(111) Epitaxial Thin Films on Atomically Stepped Sapphire (0001) Substrates

2013 ◽  
Vol 1507 ◽  
Author(s):  
Ryosuke Yamauchi ◽  
Geng Tan ◽  
Daishi Shiojiri ◽  
Nobuo Tsuchimine ◽  
Koji Koyama ◽  
...  
Keyword(s):  
Thin Films ◽  
Surface Morphology ◽  
Room Temperature ◽  
Pulsed Laser ◽  
Film Surface ◽  
Transient State ◽  
Epitaxial Thin Films ◽  
Flat Surfaces ◽  
Surface Nanostructure ◽  
Atomically Flat

ABSTRACTWe examined the influence of momentary annealing on the nanoscale surface morphology of NiO(111) epitaxial thin films deposited on atomically stepped sapphire (0001) substrates at room temperature in O2 at 1.3 × 10−3 and 1.3 × 10−6 Pa using a pulsed laser deposition (PLD) technique. The NiO films have atomically flat surfaces (RMS roughness: approximately 0.1–0.2 nm) reflecting the step-and-terrace structures of the substrates, regardless of the O2 deposition pressure. After rapid thermal annealing (RTA) of the NiO(111) epitaxial film deposited at 1.3 × 10−3 Pa O2, a periodic straight nanogroove array related to the atomic steps of the substrate was formed on the film surface for 60 s. In contrast, the fabrication of a transient state in the nanogroove array formation was achieved with RTA of less than 1 s. However, when the O2 atmosphere during PLD was 1.3 × 10−6 Pa, random crystal growth was observed and resulted in a disordered rough surface nanostructure after RTA.

Frictional Behavior of Textile Fabrics Part I: Sliding Phenomena of Fabrics on Metallic and Polymeric Solid Surfaces

1997 ◽  
Vol 67 (11) ◽  
pp. 793-802 ◽  
Author(s):  
Luis Virto ◽  
Arun Naik
Keyword(s):  
Sliding Friction ◽  
Solid Material ◽  
Solid Surfaces ◽  
Friction Behavior ◽  
Stick Slip ◽  
Compression Load ◽  
Physical Description ◽  
Frictional Behavior ◽  
Textile Fabrics ◽  
Polymeric Solid

This paper presents experimental results on the sliding of fabrics on metallic and polymeric solid surfaces, showing the influence of the compression load at the solid-fabric interface and the nature of the solid material, and the effect of sliding speed on the sliding friction coefficient. At the same time, a physical description of the sliding phenomenon is given. On the basis of these observations, a theoretical approach is developed to explain the sliding friction behavior of fabrics on solid surfaces. Part II will deal with the waving and stick-slip phenomena, which are evident in the sliding process under certain conditions.

Homo- and Hetero-Epitaxial Gallium Nitride Grown by Molecular Beam Epitaxy

1998 ◽  
Vol 537 ◽  
Author(s):  
C.T. Foxon ◽  
T.S. Cheng ◽  
D. Korakakis ◽  
S.V. Novikov ◽  
R.P. Campion ◽  
...  
Keyword(s):  
High Temperature ◽  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Defect Density ◽  
Boundary Structure ◽  
Quantum Well Structures ◽  
Flat Surfaces ◽  
Grain Boundary Structure ◽  
Bulk Gan ◽  
Atomically Flat

AbstractVarious methods have been used to initiate growth by Molecular Beam Epitaxy (MBE) of GaN on sapphire, or other substrates, but there is always a problem with morphology and with a high defect density which results in the formation of a sub-grain boundary structure. We show that by using, homo-epitaxial growth on properly prepared bulk GaN substrates, combined with high temperature growth, we obtain a significant improvement in surface morphology. Growth at sufficiently high temperature leads to a rapid smoothing of the surface and to almost atomically flat surfaces over relatively large areas. Multi-Quantum Well structures grown on such GaN epitaxial films are dislocation free with abrupt interfaces.

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