Abstract
Liquid–vapor molecular dynamics (LVMD) simulations are performed to reinvestigate the phase transition and solvation force oscillation behavior of a simple argon liquid film confined between two solid surfaces. Our simulations present a novel scenario in which the n → n − 1 layering transitions are accompanied by the formation, climb, and annihilation of Frank partial dislocations during the squeeze-out process under compression. This is indicated by the splitting of the repulsive peaks in the solvation force profile. The detailed analysis reveals that the formation–climb–annihilation mechanism of Frank dislocation occurs during approach and disappears during receding, which would result in force hysteresis. In combination with our recent works, this study provides new insights into the physical property of nanoconfined lubricant films in boundary lubrication.
Highlights
As discussed in this study, a significant aspect of the force–distance profiles obtained from the liquid–vapor molecular dynamics (LVMD) simulation is related to the asymmetric oscillations of solvation forces, i.e., the repulsive peaks are always greater than the adhesion valleys
The Polyhedral Template Matching (PTM) method is capable of identifying local crystalline structures of simple condensed phases formed by atoms ranging from some types of face-centered cubic (FCC), hexagonal close-packed (HCP), body-centered cubic (BCC), SCs, and ICOs to others
We found that the output length of dislocations two solid surfaces reveal a previously unknown scenario, in which the n → n − 1 layering depends heavily on the selection of two key parameters in the Dislocation Extraction Algorithm (DXA) process:process the trial transitions are accompanied by the formation–propagation–annihilation ofcircuit
Summary
Frictional and lubrication properties of a film in a confined geometry are affected by the way it reacts to external loading (such as compression and shear) [2,3,4,5]. A long-standing debate in surface force experiments has been the structure and shear properties of simple nonpolar lubricants confined between two solid surfaces [6,7,8,9,10,11,12,13,14,15]. The most important finding is that cyclohexane (C6 H12 ), a widely used simple model lubricant studied in surface force apparatus/balance (SFA/B) experiments, underwent a sudden liquid-like to solid-like phase transition at n < 6 monolayer thickness when confined between two molecularly smooth mica surfaces [19].
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