Temperature dependence effect of viscosity on ultrathin lubricant film melting

Abstract

We study the melting of an ultrathin lubricant film under friction between atomically flat surfaces at temperature dependencies of viscosity described by Vogel-Fulcher relationship and by power expression, which are observed experimentally. It is shown that the critical temperature exists in both cases the exceeding of which leads to the melting of lubricant and, as a result, the sliding mode of friction sets in. The values of characteristic parameters of lubricant are defined, which are needed for friction reduction. In the systems, where the Vogel-Fulcher dependence is fulfilled, it is possible to choose the parameters at which the melting of lubricant takes place even at zero temperature of friction surfaces. The deformational defect of the shear modulus is taken into account in describing the lubricant melting according to the mechanism of the first-order transition.

Phase Dynamics and Kinetics of Thin Lubricant Film Driven by Correlated Temperature Fluctuations

“…[10] the conditions under which the stick-slip friction regime corresponds to the intermittency mode inherent in self-organized criticality phenomenon are found. Effect of different types of temperature dependence of viscosity on the melting temperature of lubricant is taken into account [11].…”

A stochastic model of stick-slip boundary friction with account for the deformation effect of the shear modulus of the lubricant

“…Let us write down the system of equations for the shear components of the stresses σ and the strain ε, as well as for the temperature T, using the units [7,[10][11][12][13][14][15]17] (1) for the variables σ, ε, and T, respectively, where ρ is the lubricant density; c v is the lubricant specific heat; T c is the critical temperature; η 0 ≡ η at T = 2T c is the char acteristic value of the shear viscosity η; τ T ≡ ρl 2 c v /κ is the thermal conductivity time; l is the lubricating layer thickness; κ is the thermal conductivity of the lubri cant; τ ε is the relaxation time of strain; and G 0 ≡ η 0 /τ ε is the characteristic value of the shear modulus:…”

“…In our previous papers [7,[10][11][12][13][14][15]17], we have shown that the zero stationary stresses σ 0 correspond to the solidlike structure of the lubricant, while at σ 0 ≠ 0 the latter melts and transits to a liquidlike state, which corresponds to the plastic flow portion of the loading diagram. Transitions between the liquidlike and solid like structures are represented as phase transitions, but between different kinetic friction modes rather than between equilibrium thermodynamic phases; several kinetic friction modes may exist [1].…”

“…The numerical solution of equation (9) obtained using procedure (13), (14) is presented in Fig. 2a in the form of a phase plane portrait.…”

“…Within the limits of that theory, the effect of additive non correlated noises on lubricant melting has been studied [10], melting due to dissipative effects has been considered [11], temperature correlations [12] and various temperature dependences of the vis cosity [13] have been taken into account, and hystere sis phenomena at melting have been investigated [14,15]. However, these papers report a stochastic stick slip mode when the static and kinetic friction forces vary chaotically with time.…”