Vibrational Friction Research Articles

Current Research Status and Future Trends of Vibration Energy Harvesters.

The continuous worsening of the natural surroundings requires accelerating the exploration of green energy technology. Utilising ambient vibration to power electronic equipment constitutes an important measure to address the power crisis. Vibration power is widely dispersed in the surroundings, such as mechanical vibration, acoustic vibration, wind vibration, and water wave vibration. Collecting vibration energy is one of the research hotspots in the field of energy. Meanwhile, it is also an important way to solve the energy crisis. This paper illustrates the working principles and recent research progress of five known methods of vibrational energy harvesting, namely, electromagnetic, piezoelectric, friction electric, electrostatic, and magnetostrictive vibrational energy harvesters. The strengths and weaknesses of each method are summarised. At the end of the article, the future trends of micro-nano vibrational energy collectors are envisioned.

Atomic-scale wear behavior of two-phase TiAl alloys by vibrational horizontal friction

To investigate the influence of vibrational horizontal friction on the microscopic distortion of γ/α2 biphasic TiAl alloys, a molecular dynamics approach was used for simulation by analyzing the mechanical properties, atomic displacements, shear strains, and defect distributions of the substrate in vibrational horizontal friction and conventional friction. The friction force and coefficient of friction in vibrational horizontal friction were found to be less than conventional friction. Vibrational horizontal friction has a shallower depth of abrasion marks and a larger wear area compared to conventional friction. At the same time, this γ/α2 phase boundary changes the direction of motion of the atom so that they move in the same orientation as parallel to the interfacial boundary. Vibrational horizontal friction has a larger strain concentration area than conventional friction. The existent γ/α2 interface impedes the strain transmission so that some of the stresses are concentrated near the interface, and the γ-phase accumulates a large proportion of dislocations, which leads to work-hardening of the material. The slip of the horizontal stacking faults in the vibrational horizontal friction releases internal stresses. The formation of structures such as stacking fault tetrahedrons has a significant strengthening effect on the material.

The niobium oxoazides [NbO(N3)3], [NbO(N3)3·2CH3CN], [(bipy)NbO(N3)3], Cs2[NbO(N3)5] and [PPh4]2[NbO(N3)5

Niobium oxotriazide, [NbO(N3)3], was prepared in a fluoride-azide exchange reaction between [NbOF3] and an excess of Me3SiN3 in SO2 solution. In acetonitrile solution, the fluoride-azide exchange resulted in the isolation of the adduct [NbO(N3)3·2CH3CN]. The subsequent reaction of [NbO(N3)3] with 2,2'-bipyridine (bipy) resulted in the isolation of the bipyridine adduct [(bipy)NbO(N3)3]. The pentaazido anion [NbO(N3)5](2-) was obtained by the reaction of [NbO(N3)3] with two equivalents of ionic azide. The novel niobium oxoazides were fully characterized by their vibrational spectra, impact, friction and thermal sensitivity data and, in the case of [(bipy)NbO(N3)3], Cs2[NbO(N3)5], and [PPh4]2[NbO2(N3)5] by their X-ray crystal structures.

The Molybdenum(V) and Tungsten(VI) Oxoazides [MoO(N3)3], [MoO(N3)3⋅2 CH3CN], [(bipy)MoO(N3)3], [MoO(N3)5]2−, [WO(N3)4], and [WO(N3)4⋅CH3CN

A series of novel molybdenum(V) and tungsten(VI) oxoazides was prepared starting from [MOF4 ] (M=Mo, W) and Me3 SiN3 . While [WO(N3 )4 ] was formed through fluoride-azide exchange in the reaction of Me3 SiN3 with WOF4 in SO2 solution, the reaction with MoOF4 resulted in a reduction of Mo(VI) to Mo(V) and formation of [MoO(N3 )3 ]. Carried out in acetonitrile solution, these reactions resulted in the isolation of the corresponding adducts [MoO(N3 )3 ⋅2 CH3 CN] and [WO(N3 )4 ⋅CH3 CN]. Subsequent reactions of [MoO(N3 )3 ] with 2,2'-bipyridine and [PPh4 ][N3 ] resulted in the formation and isolation of [(bipy)MoO(N3 )3 ] and [PPh4 ]2 [MoO(N3 )5 ], respectively. Most molybdenum(V) and tungsten(VI) oxoazides were fully characterized by their vibrational spectra, impact, friction and thermal sensitivity data and, in the case of [WO(N3 )4 ⋅CH3 CN], [(bipy)MoO(N3 )3 ], and [PPh4 ]2 [MoO(N3 )5 ], by their X-ray crystal structures.

ChemInform Abstract: The First Molybdenum(VI) and Tungsten(VI) Oxoazides MO2(N3)2, MO2(N3)2·2CH3CN, (bipy)MO2(N3)2, and [MO2(N3)4]2‐ (M: Mo, W).

AbstractThe title compounds are prepared via fluoride‐azide exchange (caution: polyazides are very shock‐sensitive and can explode violently!) and characterized by vibrational spectroscopy, impact, friction, and thermal sensitivity data.

The First Molybdenum(VI) and Tungsten(VI) Oxoazides MO2(N3)2, MO2(N3)2⋅2 CH3CN, (bipy)MO2(N3)2, and [MO2(N3)4](2-) (M=Mo, W).

Molybdenum(VI) and tungsten(VI) dioxodiazide, MO2(N3)2 (M=Mo, W), were prepared through fluoride-azide exchange reactions between MO2F2 and Me3SiN3 in SO2 solution. In acetonitrile solution, the fluoride-azide exchange resulted in the isolation of the adducts MO2(N3)2⋅2 CH3CN. The subsequent reaction of MO2(N3)2 with 2,2'-bipyridine (bipy) gave the bipyridine adducts (bipy)MO2(N3)2. The hydrolysis of (bipy)MoO2(N3)2 resulted in the formation and isolation of [(bipy)MoO2N3]2O. The tetraazido anions [MO2(N3)4](2-) were obtained by the reaction of MO2(N3)2 with two equivalents of ionic azide. Most molybdenum(VI) and tungsten(VI) dioxoazides were fully characterized by their vibrational spectra, impact, friction, and thermal sensitivity data and, in the case of (bipy)MoO2(N3)2, (bipy)WO2(N3)2, [PPh4]2[MoO2(N3)4], [PPh4]2[WO2(N3)4], and [(bipy)MoO2N3]2O by their X-ray crystal structures.

The First Molybdenum(VI) and Tungsten(VI) Oxoazides MO 2 (N 3 ) 2 , MO 2 (N 3 ) 2 ⋅2 CH 3 CN, (bipy)MO 2 (N 3 ) 2 , and [MO 2 (N 3 ) 4 ] 2− (M=Mo, W)

Molybdenum(VI) and tungsten(VI) dioxodiazide, MO2(N3)2 (M=Mo, W), were prepared through fluoride–azide exchange reactions between MO2F2 and Me3SiN3 in SO2 solution. In acetonitrile solution, the fluoride–azide exchange resulted in the isolation of the adducts MO2(N3)2⋅2 CH3CN. The subsequent reaction of MO2(N3)2 with 2,2′-bipyridine (bipy) gave the bipyridine adducts (bipy)MO2(N3)2. The hydrolysis of (bipy)MoO2(N3)2 resulted in the formation and isolation of [(bipy)MoO2N3]2O. The tetraazido anions [MO2(N3)4]2− were obtained by the reaction of MO2(N3)2 with two equivalents of ionic azide. Most molybdenum(VI) and tungsten(VI) dioxoazides were fully characterized by their vibrational spectra, impact, friction, and thermal sensitivity data and, in the case of (bipy)MoO2(N3)2, (bipy)WO2(N3)2, [PPh4]2[MoO2(N3)4], [PPh4]2[WO2(N3)4], and [(bipy)MoO2N3]2O by their X-ray crystal structures.

Vibrational lifetimes and friction in adsorbate motion determined from quasi-elastic scattering.

The vibrational excitation of molecules adsorbed on a surface is typically probed by spectroscopic techniques such as infrared or Raman spectroscopy. In the present article we demonstrate an alternative method to determine vibrational lifetimes of adsorbate molecules using quasi-elastic helium atom scattering (QHAS). As a probe of diffusive motion of molecules on surfaces QHAS is well established. Here, we demonstrate that QHAS can also be used to probe the vibrational lifetime of a molecule in its adsorption well. Measurements of cyclopentadienyl, C5H5, on Cu(111) allow us to distinguish two substrate phonon modes as well as two molecular vibrational modes, perpendicular and parallel to the surface. We further find that the dephasing of the vibrational motion corresponds to the friction determined in previous diffusion measurements.

Friction-Induced Vibration by Stribeck’s Law: Application to Wiper Blade Squeal Noise

This paper is concerned with the squeal noise of a wiper/windscreen contact. It is shown that squeal noise stems from friction-induced self-excited vibrations in the context of Stribeck’s law for friction coefficient. The study is specifically focussed on the instability range of velocities and not on the amplitude of limit cycles. The studied dynamic system consists of a single degree-of-freedom mass-spring-damper oscillator submitted to a velocity-dependent frictional force which follows the Stribeck law. The local stability is analyzed by the first Lyapunov method and results in a stability criterion. Experiments have been performed on a glass/elastomer contact lubricated with water. The tribometer ‘LUG’ provides measurements of the vibrational velocity and friction force versus sliding speed. It is found that the instability appears during the transition between boundary and elastohydrodynamic regimes where the negative gradient of the friction versus velocity curve is steep. The apparition and vanishing of instability are correctly predicted by the steady-state stability criterion.

Special features of orbital and vibrational friction welding

The special features of orbital and vibrational friction welding of the components of small sections produced from identical and dissimilar materials with a specific distribution are investigated. The welding conditions are determined.

Solvent and Solvent Isotope Effects on the Vibrational Cooling Dynamics of a DNA Base Derivative

Vibrational cooling by 9-methyladenine was studied in a series of solvents by femtosecond transient absorption spectroscopy. Signals at UV and near-UV probe wavelengths were assigned to hot ground state population created by ultrafast internal conversion following electronic excitation by a 267 nm pump pulse. A characteristic time for vibrational cooling was determined from bleach recovery signals at 250 nm. This time increases progressively in H2O (2.4 ps), D2O (4.2 ps), methanol (4.5 ps), and acetonitrile (13.1 ps), revealing a pronounced solvent effect on the dissipation of excess vibrational energy. The trend also indicates that the rate of cooling is enhanced in solvents with a dense network of hydrogen bonds. The faster rate of cooling seen in H2O vs D2O is noteworthy in view of the similar hydrogen bonding and macroscopic thermal properties of both liquids. We propose that the solvent isotope effect arises from differences in the rates of solute-solvent vibrational energy transfer. Given the similarities of the vibrational friction spectra of H2O and D2O at low frequencies, the solvent isotope effect may indicate that a considerable portion of the excess energy decays by exciting relatively high frequency (>/=700 cm-1) solvent modes.

Evaluation of Nanomechanical Properties of Surfaces

The current topic related to the evaluation of the nanomechanical properties of nanometer scale surfaces is reviewed and refer to our recent results on the evaluation of the nanomechanical properties of nanoperiod multilayer solid lubricant (WS2/MoS2)n films deposited by radio frequency (RF) supttering, nanoperiod multilayer (CN/BN)n films deposited by RF sputtering, diamondlike carbon (DLC) films deposited by a bend type filtered cathodic vacuum arc (FCVA) technique and a lubricant on perpendicular-recording magnetic disks. In the field of micro-nano technology, nanoscale evaluation technology is necessary and important for determining surface properties, particularly mechanical properties. The evaluation of thin-film surfaces has been performed by nanoindentation tests and nanoscratch tests using an atomic force microscope. On the other hand, as nanowear tests have enabled the evaluation of the average mechanical properties of a thin-film surface, it has become possible to evaluate a difference of about 0.1 nm by choosing appropriate loads. The properties of vibrational nanoprocessing, surface friction, viscoelastic properties and other dynamic properties can be evaluated by applying a force modulation method using scanning probe microscope (SPM). Moreover, when characterizing a surface it is effective to evaluate mechanical properties and other physical properties simultaneously. Surface damage and lubricant conditions have been studied by measuring the friction force and current distribution in lateral vibration tests.

Temperature-Dependent Protein Dynamics: A Simulation-Based Probabilistic Diffusion-Vibration Langevin Description

An enduring challenge in the understanding of internal protein motions is the effective separation and characterization of diffusive and vibrational dynamical components. To address this problem, here nanosecond molecular dynamics trajectories of myoglobin in aqueous solution, performed over a range of temperatures between 120 and 300 K, are subjected to principal component analysis, and the coordinate autocorrelation functions of the resulting principal modes are interpreted using a model combining damped Langevin vibration within potential wells and barrier-crossing diffusion between them. Both the vibrational frequency and the fraction of the mean-square fluctuation arising from vibrational motion undergo transitions with temperature at about 180 K. In contrast, the vibrational friction remains linear with temperature. The diffusional component of the mean-square fluctuation increases dramatically at the dynamical transition. The heights of the energy barriers between the potential wells are estimated, and the associated diffusion constants are calculated using Kramers' rate theory. Model functions of the frequency dependence of the frictional and diffusional quantities are obtained. The dynamic structure factor from the full molecular dynamics trajectory is well reproduced by the model. Overall, the results indicate that a global description of nanosecond temperature-dependent diffusion and vibrational internal protein dynamics can be obtained by applying the results of the present diffusion-vibration model to the vibrational motions obtained from a normal-mode analysis.

The workings of a molecular thermometer: the vibrational excitation of carbon tetrachloride by a solvent.

An intriguing energy-transfer experiment was recently carried out in methanol/carbon tetrachloride solutions. It turned out to be possible to watch vibrational energy accumulating in three of carbon tetrachloride's modes following initial excitation of O-H and C-H stretches in methanol, in effect making those CCl(4) modes "molecular thermometers" reporting on methanol's relaxation. In this paper, we use the example of a CCl(4) molecule dissolved in liquid argon to examine, on a microscopic level, just how this kind of thermal activation occurs in liquid solutions. The fact that even the lowest CCl(4) mode has a relatively high frequency compared to the intermolecular vibrational band of the solvent means that the only solute-solvent dynamics relevant to the vibrational energy transfer will be extraordinarily local, so much so that it is only the force between the instantaneously most prominent Cl and solvent atoms that will significantly contribute to the vibrational friction. We use this observation, within the context of a classical instantaneous-pair Landau-Teller calculation, to show that energy flows into CCl(4) primarily via one component of the nominally degenerate, lowest frequency, E mode and does so fast enough to make CCl(4) an excellent choice for monitoring methanol relaxation. Remarkably, within this theory, the different symmetries and appearances of the different CCl(4) modes have little bearing on how well they take up energy from their surroundings--it is only how high their vibrational frequencies are relative to the solvent intermolecular vibrational band edge that substantially favors one mode over another.

Molecular dynamics study of the vibrational relaxation of OCl and OCl − in the bulk and the surface of water and acetonitrile

The vibrational relaxation of OCl and OCl − in the bulk and the liquid/vapor interface of water and acetonitrile is studied by molecular dynamics computer simulations. Both equilibrium calculations of the vibrational friction and non-equilibrium simulation of the energy relaxation are used to elucidate the factors that influence the rate of energy relaxation in systems that represent polar ionic and non-ionic solutes in polar protic and non-protic solvents. We find that, in agreement with previous experimental and theoretical studies, the relaxation of the ionic solute is much faster than that of the non-ionic solute in both the solvents. However, while the relaxation is slowed down considerably when the non-ionic solute is transferred from the bulk to the interface, no such surface effect is found in the case of the ionic solute. This behavior can be explained by noting that the ionic solute is able to keep its first solvation shell intact upon transfer to the interface and that the main contribution to the friction is due to the Lennard-Jones part of the intermolecular potential.

Molecular Dynamics Simulation of Vibrational Friction Force Due to Molecular Deformation in Confined Lubricant Film

The lubrication by thin film has become a very important role in micro machine, magnetic storage device and so on. As the thickness of lubricant film becomes thinner to several nanometers, the conventional law of lubrication becomes unable to use. Nonequilibrium molecular dynamics simulation (NEMD) was carried out to investigate the dynamic behavior of thin lubricant film confined between walls. The model used in these simulations is composed of two solid walls and fluorocarbon polymer lubricant. One of the walls is supporting a load and at the same time moving at constant velocity. Results indicate that the frictional behavior of confined lubricant varied with load; velocity field in the film retain liquid like structure under low load conditions, on the other hand, under high load conditions lubricant film becomes solidified and periodical stick and slip motion is observed at the layer near the wall. At the same time periodically vibrating friction force is observed. In this case, radius of gyration of lubricant molecules also changes periodically. It is concluded that the periodical vibration of friction force is caused by stick-slip with molecular deformation.

Time correlation function approach to liquid phase vibrational energy relaxation: Dihalogen solutes in rare gas solvents

A molecular theory of liquid phase vibrational energy relaxation (VER) [S. A. Adelman et al., Adv. Chem. Phys. 84, 73 (1993)] is applied to study the temperature T and density ρ dependencies of the VER rate constant k(T,ρ)=T1−1, where T1 is the energy relaxation time, of model Lennard-Jones systems that roughly simulate solutions of high-mass, low-frequency dihalogen solutes in rare gas solvents; specifically the I2/Xe, I2/Ar, and ICI/Xe solutions. For selected states of these systems, the theory’s assumptions are tested against molecular dynamics (MD) results. The theory is based on the expression T1=β−1(ωl), where ωl and β(ω) are, respectively, the solute’s liquid phase vibrational frequency and vibrational coordinate friction kernel. The friction kernel is evaluated as a cosine transform of the fluctuating force autocorrelation function of the solute vibrational coordinate, conditional that this coordinate is fixed at equilibrium. Additionally, the early-time decay of the force autocorrelation function is approximated by a Gaussian function which is exact to order t2. This Gaussian approximation permits evaluation of T1 in terms of integrals over equilibrium solute–solvent pair correlation functions. The pair correlation function formulas yield T1’s in semiquantitative agreement with those found by MD evaluations of the Gaussian approximation, but with three orders of magnitude less computational effort. For the isothermal ρ dependencies of k(T,ρ), the theory predicts for all systems that the Gaussian decay time τ is nearly independent of ρ. This in turn implies that k(T,ρ) factorizes into a liquid phase structural contribution and a gas phase dynamical contribution, yielding a first-principles form for k(T,ρ) similar to that postulated by the isolated binary collision model. Also, the theory predicts both “classical” superlinear rate isotherms, and “nonclassical” sublinear isotherms similar to those recently observed by Troe and co-workers for azulene relaxation in supercritical fluids. The isochoric T dependencies of k(T,ρ) are studied in the range 300 to 1000 K. For none of the solutions are the rate isochores found to accurately conform to either Arrhenius or Landau–Teller kinetics.

Vibrational energy relaxation of polyatomic molecules in liquids: The solvent’s perspective

Vibrationally excited polyatomic molecules can relax in a variety of different ways in solution; the excess energy can be dissipated directly to the solvent, or it can be redistributed between any number of different intramolecular modes, with the liquid absorbing (or supplying) just enough energy to make the process work. What we consider here is how the solvent participates in these mechanistic choices. Using the prototypical example of a symmetric linear triatomic molecule, we compare the molecular origins of the vibrational friction for the direct vibrational cooling of the symmetric and antisymmetric stretching modes and contrast both of those with intramolecular vibrational energy transfer between these two modes. Instantaneous-normal-mode analysis reveals that a solid-statelike perspective is a plausible starting point for understanding these processes; the solvent does define a band of intermolecular vibrations, and it is only when the energy being transferred falls within that band that the solvent can easily accept energy from a solute. However, it is also possible to discern some more liquid-state-specific details. Despite their different symmetries and different kinematic requirements, all of the different relaxation pathways are apparently driven by the dynamics of the same instantaneously nearest solvents.

The short-time intramolecular dynamics of solutes in liquids. II. Vibrational population relaxation

Events such as the vibrational relaxation of a solute are often well described by writing an effective equation of motion—a generalized Langevin equation—which expresses the surrounding medium’s influence on the intramolecular dynamics in terms of a friction and a fluctuating force acting on the solute. These quantities, though, can be obtained from the instantaneous normal modes (INMs) of the system when the relaxation takes place in a fluid, suggesting that we should be able to analyze in some detail the solvent motions driving the relaxation, at least for short times. In this paper we show that this promise can indeed be realized for the specific case of a vibrating diatomic molecule dissolved in an atomic solvent. Despite the relatively long times typical of vibrational population relaxation, it turns out that understanding the behavior of the vibrational friction at the short times appropriate to INMs (a few hundred femtoseconds) often suffices to predict T1 times. We use this observation to probe the dependence of these relaxation rates on thermodynamic conditions and to look at the molecular mechanisms underlying the process. We find that raising the temperature at any given density or raising the density at any given temperature will invariably increase the rate of energy relaxation. However, since these two trends may be in conflict in a typical constant-pressure laboratory experiment, we also find that it is possible to make sense of the “anomalous” inverted temperature dependence recently seen experimentally. We find, as well, that the INM theory—which has no explicit collisions built into it—predicts exactly the same density dependence as the venerable independent-binary-collision (IBC) theory (an intriguing result in view of recent claims that experimental observations of this kind of dependence provide support for the IBC theory). The actual mechanisms behind vibrational population relaxation are revealed by looking in detail at the vibrational friction “influence spectrum”—the spectrum of INMs weighted by how efficiently each mode acts to promote the relaxation. Through suitable projections we show that the average influence spectrum is dominated by longitudinal motion of the solvent atoms in the first solvation shell. We go further, however, and examine the nature of the instantaneous relaxation promoted by individual liquid configurations. The number of instantaneous modes that contribute significantly fluctuates strongly from configuration to configuration, and the number of solvent atoms strongly coupled to the solute has a certain amount of variation as well, but invariably each significant mode ends up promoting the relaxation by moving just one or two significant solvent atoms—a feature we explore in a companion paper.

Switch Phenomena in Molecular Three-Centre Electron Transfer Systems with Strong Electronic-Vibrational Coupling

Abstract Three-centre molecular and supramolecular electron transfer (ET) is important in device-like function of organized assemblies of bridge-group separated donor and acceptor units in solid-state or electrochemical systems. Other areas are solid-state phonon-kick charge capture, electrochemical ET via adsorbates or film impurities, large adsorbate STM, and long-range ET in redox metalloproteins. Optical three-level analogues are molecular Raman scattering and two-photon absorption. Three-level ET behaviour rests on coupling to environmental nuclear motion. A frame is second order perturbation theory including full vibrational manifolds in all three states. We discuss such a formalism. Common superex-change is recovered for high intermediate state energies while vibrationally unrelaxed state population emerges for low energies. These limits are separated by finite resonances in characteristic “switch” patterns. Intermediate state vibrational friction is briefly addressed and we note some biological and synthetic systems to which the formalism is appropriate.