Predicting the lifetime of superlubricity

Abstract

The concept of superlubricity has recently called upon notable interest after the demonstration of ultralow friction between atomistically smooth surfaces in layered materials. However, the energy dissipation process conditioning the sustainability of superlubric state has not yet been well understood. In this work, we address this issue by performing dynamic simulations based both on full-atom and reduced Frenkel-Kontorova models. We find that the center-of-mass momentum autocorrelation of a sliding object can be used as an indicator of the state of superlubricity. Beyond a critical value of it, the sliding motion experiences catastrophic breakdown with a dramatically high rate of energy dissipation, caused by the inter-vibrational-mode coupling. By tracking this warning signal, one can extract heat from modes other than the translation to avoid the catastrophe and extend the lifetime of superlubricity. This concept is demonstrated in double-walled carbon nanotubes based nanomechanical devices with indicator-based feedback design implemented. 2With the wide and increasing applications of micro-and nano-mechanical devices, friction between contact parts becomes a crucial factor determining their performance and service time due to the important energy dissipation and material loss it causes. The occurrence of dramatically diminishing friction force between two 'completely clean' or atomistically smooth solid surfaces, named as superlubricity, was firstly coined by Hirano and Shinjo [1], and potentially offers a perfect solution to this problem. Graphitic systems have been explored to test this idea recently [2][3][4][5]. A superlubric state has been identified at a length-scale of a few micrometers and a time-scale of microseconds, with ultralow frictional force characterized [6]. However, no proof has yet been available to establish the superlubric state in a practical length and time scale for real-world applications. Theoretical studies [7][8][9] show that even for atomistically smooth surfaces in contact, catastrophic breakdown of the superlubric state could occur by leaking a significant amount of kinetic energy in the mechanical motion of operation to the rest or, in other words, heat. Based on their studies on a Frenkel-Kontorova (F-K) chain model, Consoli et al. [7] concluded that dissipative parametric resonance between vibrational modes in the chain results in the onset of friction in an incommensurate system. This phenomenon was later observed in the relative sliding of concentric graphitic walls in double-walled carbon nanotubes (DWCNTs) [8], and the origin of the identified catastrophic kinetic energy leaking is attributed to the resonant coupling between the translational motion and radial breathing modes. Similar phenomenon was recently reported for sliding motion between graphitic layers, demonstrating a transition in frictional state as the graphite flake rotates through successive crystallographic alignments with the substrates [9]. Although significant progress has been made, understan...

Robustness of structural superlubricity beyond rigid models

“…It should be noted, although lattice distortion reduces friction stress at interfaces with initial Bernal stacking, the lattice slips and phononic excitation play an important role in the kinetic friction of graphitic superlubricity systems [10]. At high sliding speeds, catastrophic damping effects were reported in the resonant regime [37,52,53]. With the size of contact much beyond the width of strained solitons, the nucleation of domains with local Bernal stacking could increase mechanical energy It should also be remarked here that the simulations and theoretical models in our work and the literature are mostly restricted by their one-dimensional (1D) setup.…”

Physical scientist or a data scientist? A journey between disciplines

“…The energy flow between different principal modes of motion elucidates the mechanisms of mechanical excitation and energy dissipation. 4 , 5 In this analysis, the rigid-body motion can be distinguished from the molecular or lattice vibrations, and we identified the catastrophic events of dissipation that correspond to their resonant coupling. By defining and monitoring the statistical indicators, we devised the early warning signals to predict the occurrence of these critical events and prevent them in advance.…”

“…By defining and monitoring the statistical indicators, we devised the early warning signals to predict the occurrence of these critical events and prevent them in advance. 4 , 5 The evolution of this work and the insights I received from the statistical analysis of the time-series space-time data motivated me to use data-driven models and methods to understand the physics of complex systems.…”