Rougher is more slippery: How adhesive friction decreases with increasing surface roughness due to the suppression of capillary adhesion (original) (raw)

Resource Letter: FMMLS-1: Friction at macroscopic and microscopic length scales

American Journal of Physics, 2002

This Resource Letter provides a guide to the literature on the fundamental origins of friction. Books, reviews, and journal articles are cited for the following topics: History of friction and tribology, the adhesion theory of macroscopic friction, first principles' treatments of frictional energy dissipation at the atomic level, experimental methods for studying friction at the atomic-scale, stick-slip phenomena and lattice commensurability effects.

Frictional properties of interfaces including multiple microscopic contacts

2019

Frictional properties of interfaces with dynamic chemical bonds have been the subject of intensive experimental investigation and modelling, as it provides important insights into the molecular origin of the empirical rate and state laws, which have been highly successful in describing friction from nano to geophysical scales. Using previously developed theoretical approaches requires time-consuming simulations that are impractical for many realistic tribological systems. To solve this problem and set a framework for understanding microscopic mechanisms of friction at interfaces including multiple microscopic contacts, we developed an analytical approach for description of friction mediated by dynamical formation and rupture of microscopic interfacial contacts, which allows to calculate frictional properties on the time and length scales that are relevant to tribological experimental conditions. The model accounts for the presence of various types of contacts at the frictional inter...

The Dynamics of Friction: An Interdisciplinary Exploration of Its Role in Real-World Physics

Salma A. Ali, 2024

Friction is a fundamental force that governs interactions across diverse physical systems, influencing motion, energy transfer, and material behavior. This article provides an in-depth exploration of the various types of friction-static, kinetic, rolling, and fluid-and their intricate interplay within the realms of physics, engineering, biology, and environmental science. By examining the coefficient of friction, surface roughness, and energy dissipation, we elucidate how frictional forces are not merely resistive but also enable critical functions, such as propulsion in transportation, stability in structural design, and efficiency in mechanical systems. Additionally, the role of friction in human biomechanics highlights its significance in motion and ergonomics, demonstrating its relevance to health sciences. Through an interdisciplinary lens, we reveal that friction is integral to the design and optimization of technologies ranging from everyday appliances to advanced engineering applications. Ultimately, this comprehensive analysis underscores the necessity of understanding friction's multifaceted role, fostering innovative solutions that harness its properties for improved performance and sustainability in both natural and engineered systems.

From Molecular to Multiasperity Contacts: How Roughness Bridges the Friction Scale Gap

ACS Nano, 2023

Friction is a pervasive phenomenon that affects the mechanical response of natural and man-made systems alike, from vascular catheterization to geological faults responsible for earthquakes. While friction stems from the fundamental interactions between atoms at a contact interface 1-3 , its best descriptions at the macroscopic scale remain phenomenological 4. The so called "rate-and-state" models 5-8 , which specify the friction response in terms of the relative sliding velocity and the "age" of the contact interface 9 , fail to uncover the nano-scale mechanisms governing the macro-scale response, while models of friction at the atomic scale often overlook how roughness can alter the friction behavior. Here we bridge this gap between nano and macro descriptions for friction by correlating the physical origin of macroscopic friction to the existence, due to nanometric roughness, of contact junctions between adsorbed monolayers, whose dynamics, as we show, emerges from molecular motion. Through coupled experimental and atomic simulations we were able to highlight that transient friction overshoots after the system is allowed to rest with the friction force decaying to a steady-state value over a characteristic distance 0 = 3.5 nm, all despite a roughness of 0.6 nm. Our atomistic simulations link this characteristic scale to the evolution of the number of cross-surface links and paint contact junctions as a necessary component in the observation of the transient friction overshoot. This is finally validated by a multi-scale-in both time and space-unified theoretical approach which accurately predicts the transient friction response. Our results demonstrate that a fundamental understanding of the contact junctions caused by nanometric roughness is instrumental in lifting the phenomenological veil over macro-scale friction models. We expect our findings to usher in a new class of friction models that account for the roughness, and to help unify the nano and macro friction communities, from biology to geophysics.

The nature of friction: A critical assessment

Friction, 2013

Friction is an essential part of human experience. We need traction to walk, stand, work, and drive. At the same time, we need energy to overcome the resistance to motion, hence, too much friction costs excess energy to perform work, introducing inefficiencies. In the 21st century, we are facing the dual challenges of energy shortage and global warming from burning fossil fuels. Therefore, the ability to control friction has become a top priority in our world today. Yet our understanding of the fundamental nature of friction is still lacking. Friction has always been a subject of curiosity. Intensive study of the origin of friction began in the 16th century, after the pioneering work by Leonardo da Vinci. Yet progress in understanding the nature of friction has been slow, hampered by the lack of instrument to measure friction precisely. Ingenious experiments performed by Amontons, Coulomb, and others have yielded important insights to build the foundation of our understanding. Begin...

Friction mechanisms at the micro-scale

Tribology International, 2009

Contact between macroscopic surfaces occurs on asperities and local nano-/micro-scale asperity interactions govern macroscopic tribological behavior. Tribological phenomena like friction and wear are highly scale dependent. Friction measurement carried out in the range of micro-/milli-Newton loads are gaining prominence in the tribological research as they are bridging the gap between classical macro-scale tests and high precision nano-scale experiments. In this paper, recent advancements in micro-scale domain are discussed and compared with the existing macro-and nano-scale friction research. There exists a striking similarity between micro-and nano-scale frictional behavior of various materials and dependence of friction on capillary forces, surface topography, and phase composition of mated materials. Micro-tribological experiments not only offer precision and sensitivity of nano-scale (or LFM) measurements, but also give reliable information due to its multiple asperity contact configuration. Fig. 12. (a) Fiber optic sensor based micro-tribometer and (b) cantilever sensor system.

Load-velocity-temperature relationship in frictional response of microscopic contacts

Journal of the Mechanics and Physics of Solids, 2020

Frictional properties of interfaces with dynamic chemical bonds have been the subject of intensive experimental investigation and modelling, as it provides important insights into the molecular origin of the empirical rate and state laws, which have been highly successful in describing friction from nano to geophysical scales. Using previously developed theoretical approaches requires time-consuming simulations that are impractical for many realistic tribological systems. To solve this problem and set a framework for understanding microscopic mechanisms of friction at interfaces including multiple microscopic contacts, we developed an analytical approach for description of friction mediated by dynamical formation and rupture of microscopic interfacial contacts, which allows to calculate frictional properties on the time and length scales that are relevant to tribological experimental conditions. The model accounts for the presence of various types of contacts at the frictional interface and predicts novel dependencies of friction on sliding velocity, temperature and normal load, which are amenable to experimental observations. Our model predicts the velocitytemperature scaling, which relies on the interplay between the effects of shear and temperature on the rupture of interfacial contacts. The proposed scaling can be used to extrapolate the simulation results to a range of very low sliding velocities used in nanoscale friction experiments, which is still unreachable by simulations. For interfaces including two types of interfacial contacts with distinct properties, our model predicts novel double-peaked dependencies of friction on temperature and velocity. Considering friction force microscopy experiments (FFM), we found that the non-uniform distribution of normal load across the interface leads to a distribution of barrier heights for contact formation. The results obtained in this case allowed to reveal a mechanism of nonlinear dependence of friction on normal load observed in recent FFM experiments and predict the effect of normal load on velocity and temperature dependencies of friction. Our work provides a promising avenue for the interpretation of the experimental data on friction at interfaces including microscopic contacts and open new pathways for the rational control of the frictional response.

Interfacial friction at action: Interactions, regulation, and applications

Friction, 2023

Friction is a fundamental force that impacts almost all interface-related applications. Over the past decade, there is a revival in our basic understanding and practical applications of the friction. In this review, we discuss the recent progress on solid-liquid interfacial friction from the perspective of interfaces. We first discuss the fundamentals and theoretical evolution of solid-liquid interfacial friction based on both bulk interactions and molecular interactions. Then, we summarize the interfacial friction regulation strategies manifested in both natural surfaces and artificial systems, focusing on how liquid, solid, gas, and hydrodynamic coupling actions mediate interfacial friction. Next, we discuss some practical applications that are inhibited or reinforced by interfacial friction. At last, we present the challenges to further understand and regulate interfacial friction.

Micromechanics of friction: effects of nanometre-scale roughness

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2008

Nanometre-scale roughness on a solid surface has significant effects on friction, since intersurface forces operate predominantly within a nanometre-scale gap distance in frictional contact. To study the effects of nanometre-scale roughness, two novel atomic force microscope friction experiments were conducted, each using a gold surface sliding against a flat mica surface as the representative friction system. In one of the experiments, a pillar-shaped single nano-asperity of gold was used to measure the molecular-level frictional behaviour. The adhesive friction stress was measured to be 264 MPa and the molecular friction factor 0.0108 for a direct gold–mica contact. The nano-asperity was flattened in contact, although its hardness at this length scale is estimated to be 3.68 GPa. It was found that such a high pressure could be reached with the help of condensed water capillary forces. In the second experiment, a micrometre-scale asperity with nanometre-scale roughness exhibited a ...