Modeling friction: From nanoscale to mesoscale (1112.3234v4)

Abstract: The physics of sliding friction is gaining impulse from nanoscale and mesoscale experiments, simulations, and theoretical modeling. This Colloquium reviews some recent developments in modeling and in atomistic simulation of friction, covering open-ended directions, unconventional nanofrictional systems, and unsolved problems.

• The paper reviews key friction models, including the Prandtl-Tomlinson and Frenkel-Kontorova models, to explain atomic-scale stick-slip behavior and superlubricity.
• It employs molecular dynamics simulations to investigate temperature and velocity effects while addressing challenges like realistic damping and scale bridging.
• The paper emphasizes multicontact and mechano-kinetic models, advocating integrated thermo-mechanical approaches to extend insights from nano to mesoscopic scales.

Modeling Friction: From Nano to Meso Scales

The paper "Modeling friction: from nano to meso scales" provides an extensive review of developments in the modeling and atomistic simulation of sliding friction, emphasizing nano and mesoscopic scales. The authors comprehensively discuss several critical models and methodologies for understanding frictional phenomena across different scales.

The authors begin by revisiting the classical phenomenological laws of friction and highlight the emerging complexity at microscopic scales. The classical Coulomb-Amontons laws describe frictional force as independent of the contact area and proportional to the normal load, but they do not account for the advances in non-equilibrium statistical mechanics and materials science at smaller scales.

Key Models and Methodologies

The discourse transitions into discussing "minimalistic" models such as the Prandtl-Tomlinson (PT) model, which serves as a fundamental framework to understand atomic-scale friction. The PT model encapsulates the stick-slip behavior, a recurring phenomenon where sliding occurs intermittently, characterized by periods of sticking followed by sudden slips. This stick-slip phenomenon is central to understanding kinetic friction in nano-scale systems.

The paper details extensions to the PT model, incorporating thermal effects, and delineating regimes where friction exhibits a dependence on tip velocity and temperature. These extensions provide insights into velocity and temperature dependencies of nanoscale friction, addressing phenomena such as thermolubricity—where friction decreases at low velocities due to thermal activation.

Another critical model discussed is the Frenkel-Kontorova (FK) model, traditionally used to describe dislocations in crystals. It is used for understanding incommensurate sliding, where lattice mismatch between two surfaces leads to reduced friction—a state potentially achieving superlubricity.

Molecular Dynamics and Simulation Challenges

The authors highlight the contributions of Molecular Dynamics (MD) simulations in providing a microscopic understanding of friction at the atomic scale. These simulations elucidate interactions at sliding interfaces but face challenges such as the computational cost and scale limitations, especially when attempting to capture realistic time-scales and lengths observed experimentally. While MD provides valuable insights into phenomena like the transition from stick-slip to smooth sliding, limitations arise from unrealistic damping, size effects, and atomistic to continuum model transitions.

Multicontact and Mesoscopic Models

To bridge nano to meso scales, the paper discusses multicontact models. These models consider the real interface comprising a multitude of microscopic contacts, each contributing collectively to the macroscopic frictional response. The authors outline how mechano-kinetic models describe friction via dynamic rupture and reformation of these contacts, capturing the complex interplay between kinetic detachments and reattachment of junctions.

The paper underscores the necessity for developing effective thermo-mechanical models and mesoscopic approaches offering insights into wear, adhesion, and roll-sliding interactions at larger scales. These models aim to address limitations in transferring knowledge from nano to macroscale phenomena.

Special Phenomena and Future Directions

Special frictional phenomena such as electronic friction and magnetic dissipation are discussed as important areas illustrating complex interactions at surfaces—potentially opening avenues in utilizing external fields to modulate friction.

The paper calls for future advancements in multiscale approaches and emphasizes challenges such as realistic dissipation mechanisms and bridging computational with experimental observations. The researchers stress the importance of fundamental advancements in friction theory, advocating for integrative approaches combining simulation, theoretical development, and experimental validation.

In conclusion, while significant progress has been made in understanding nanoscale friction, challenges persist in extending these insights to macroscopic levels and non-equilibrium statistical descriptions. The field continues to evolve with emerging technologies and methodologies offering new perspectives in the paper of friction from nano to mesoscale.