Multidimensional thermodynamic potential for descriptions of ultrathin lubricant film melting between two atomically smooth surfaces

Abstract

The thermodynamic model of ultrathin lubricant film melting, confined between two atomically-flat solid surfaces, is built using the Landau phase transition approach. Non-equilibrium entropy is introduced describing the part of thermal motion conditioned by non-equilibrium and non-homogeneous character of the thermal distribution. The equilibrium entropy changes during the time of transition of non-equilibrium entropy to the equilibrium subsystem. To describe the condition of melting, the variable of the excess volume (disorder parameter) is introduced which arises due to chaotization of a solid structure in the course of melting. The thermodynamic and shear melting is described consistently. The stick-slip mode of melting, which is observed in experiments, are described. It is shown that with growth of shear velocity, the frequency of stiction spikes in the irregular mode increases at first, then it decreases, and the sliding mode comes further characterized by the constant value of friction force. Comparison of the obtained results with experimental data is carried out.

Vacancy theory of melting

“…Earlier in a phenomenological variant, the approach was applied for the description of processes of defect formation and work hardening in metals treated by severe plastic deformation [30][31][32][33], auto-vibration transitions between the amorphous and nanocrystalline states in amorphous alloys [56], processes of slipping and stickslip in the super-thin lubricants [57,58]. In particular, within the indicated models, to describe the stick-slip effects the processes of transitions between solid and liquid states, that is, processes of melting and solidification, are examined.…”

If holm had used a Scanning Tunneling Microscope: What the nanoscientists are teaching us about electrical contacts

“…This phase transition from solid-like to liquid-like is used to explain a number of stick-slip friction phenomena in sliding contacts since the transition point has been shown to be very sensitive to the shear force and velocity of the sliding member [54][55][56]. Thermodynamic effects work in conjunction with shear effects to control the transition point of the phase transition of the constrained film [58,59]. Fig.…”

“…Values of temperatures of friction surfaces are T e0 =50K, T e1 =230K, T e2 =400K, T e3 =490K, T e4 =550K. Reprinted from[58] …”

Melting Is Well-Known, but Is It Also Well-Understood?

“…Other authors − have also dealt with vacancy theory for melting. Generally, they all take the same general form but differ in detail.…”