Highlights

Workshop on Molecular Mechanisms of Tribochemistry and Lubrication

M. Clelia Righi organized a Workshop with Chris Lorenz (King’s College, London) and Eddy Tysoe (University of Wisconsin-Milwaukee) about the Molecular Mechanisms of Tribochemistry and Lubrication at the CECAM Headquarters at Ecole Polytechnique Fédérale de Lausanne, Switzerland, from 27 to 29 January 2020. World experts in this field, both theorists and experimentalists, will participate to discuss new strategies in designing materials and systems to overcome today’s challenges in tribology. The objectives of this event are to find the best possible computational strategies to face complex tribological problems, to shed light on the fundamental aspects of the tribochemical reactions such as the effect of load, shear stress, confinement, and better understand how to control molecular-level mechanisms of friction and wear.


Publication on Physical Review Letters

Michael Wolloch, Clelia Righi and Paolo Restuccia

The study Interfacial Charge Density and Its Connection to Adhesion and Frictional Forces was published on Physical Review Letters in 2018. The connection between tribological and electronic properties of interfaces has become clear with the contribution of the Unimore researchers Michael Wolloch, Paolo Restuccia, Giacomo Levita and M. Clelia Righi.

Friction is a very common phenomenon, from nanotechnologies to earthquakes, and it is well studied since Leonardo da Vinci. However, the fundamental origin of friction is still not completely understood.

Through computer simulations, we demonstrated that adhesive friction depends on how interfacial charge redistributes while the two surfaces slide against each other.

– Clelia Righi

Full article (in Italian)


Publication on Physical Review Letters

Tribochemical reactions of water molecules at diamond interface

In Load-induced confinement activates diamond lubrication by water, an article published by G. Zilibotti, S. Corni and M. C. Righi on Physical Review Letters in 2013, the first ab initio molecular dynamics simulations of a sliding interfaces have been described.

Tribochemical reactions are chemical processes, usually involving lubricant or environment molecules, activated at the interface between two solids in relative motion. They are difficult to be monitored in situ, which leaves a gap in the atomistic understanding required for their control. Here we report the real-time atomistic description of the tribochemical reactions occurring at the interface between two diamond films in relative motion, by means of large scale ab initio molecular dynamics. 

– Clelia Righi

Events with students

The group has frequent interactions with students from high school. The Physics Department of Unimore hosts students in several occasions to introduce them to scientific research. Students can stay for a single day or longer periods depending on the proposed activities. One of the students who visited the group, Aleksandar Glišić, is acknowledged for precious contributions to the present website.

Righi’s group participated also to Unimore Orienta (2019, 2018, 2017 editions), where students from high school visit the University in an “Open day” event. They can meet members of the computational materials and tribology group presenting some highlights of the research.

SLIDE

M. Clelia Righi obtained an European Research Council (ERC) Consolidator Grant 2019 for the project Advancing Solid interfaces and Lubricants by fIrst principles material DEsign (SLIDE).
Friction and wear are common phenomena that impact all applications where moving components are in contact, from micro-electromechanical systems to wind turbines, and result in massive economic and environmental costs. By advancing tribological materials impressive energy savings, and consequent reduction of CO
2 emissions, can be obtained. However, optimizing lubricant materials is challenging because their performances are ruled by molecular-level processes that occur at the buried interface, which are extremely difficult to monitor by experiments. Simulations can play a decisive role here, in particular those based on quantum mechanics, which is essential to accurately describe the interactions between surfaces in contact and simulate reactions in conditions of enhanced reactivity as those imposed by the mechanical stresses applied.
The goal of SLIDE is to port the material design paradigm based on First Principles Material Discovery to the field of Tribology by the development and applications of I) a protocol for harnessing tribochemical reactions to reduce interface friction II) a workflow for high throughput screening of solid interfaces.


Collaboration with Total

Kick-off meeting, 2018

M. Clelia Righi collaborates with Total S.A. for the computational design of lubricant additives since 2012. The objectives of the last research project, started in 2017, have been presented during a “Kick-off meeting” at Unimore, which was attended by the Rector Prof. A. Andrisano, and Total managers.

The project with Total focuses on a lubricant additive based on molybdenum and sulfur, which is commonly used in car engines. The objective is to understand the chemical reactions activated by mechanical stresses which lead to the formation of friction-reducing tribofilms.

– Clelia Righi

Full article (in Italian)

Dossier – local press (in Italian)


Publication on ACS Nano

Microscopic tip on graphene

Altering the Properties of Graphene on Cu(111) by Intercalation of Potassium Bromide is a study published on the journal ACS Nano in 2019 by Prof. M. Clelia Righi and Dr. Paolo Restuccia in collaboration with the University of Basel.

Interaction of graphene with a metallic substrate negatively affects the optical properties of graphene.

Our simulations, based on the experimental observations obtained at the University of Basel, reveal that potassium bromide is able to decouple graphene and the metal substrate, and preserve the remarkable properties of graphene.

– Clelia Righi

The publication


Public events

Complesso San Geminiano (Modena), September 2018

Righi’s computational tribology group takes part actively in events for the general public. One of these is the European Research Night, an opportunity for researchers to present their work to non-specialists and young people. In Modena, the event takes place in the city center and Righi’s group participates by presenting tribology and the role of computer simulations in designing materials for applications.

Collaboration with Toyota

Seiji Kajita and Clelia Righi

Toyota Central R&D Labs. based in Nagakute, Japan, renewed a collaboration with the research group of M. C. Righi at the Physics Department of Unimore to study tribological phenomena.

Toyota contacted me after the International Tribology Conference (ITC) held in Hiroshima in 2011. There I presented the first ab-initio molecular dynamics simulations applied to tribology. These simulations allow a better understanding of the reactions occurring at the buried interface. The novelty of this approach attracted interest in the tribology community and industries.

– Clelia Righi

Full article (in Italian)


Publication on PNAS

A domain of particles (in blue) that have moved in the direction of the external force nucleates and, at a critical size, drag the whole system transition into motion

In Onset of frictional slip by domain nucleation in adsorbed layers, a work published in Proceedings of the National Academy of Sciences in 2010, M. Reguzzoni, M. Ferrario, S. Zapperi and M. C. Righi show that the onset of slip is a nucleation process.

Creep motion matters in a variety of fields: In materials science, creep of grain boundaries makes it challenging to predict the longevity of material properties with potential implications for nuclear power plants or railway wheels. In Earth science, creep plays a critical role in the motion of tectonic plates. […]  
Theorists cannot apply their beloved tools – such as linear-response theory – to creep phenomena in a straightforward fashion. This is why it is difficult to develop a theory for creep motion, which is precisely what Reguzzoni et al. succeeded in doing for a specific system in this issue of PNAS. Their work is impressive because they not only derive the functional relationship between creep motion and external force, but they manage to ascertain the correct material-specific parameters with surprisingly simple and thus elegant analytical calculations.

– Martin H. Müser, PNAS January 26, 2010 107 (4) 1257-1258

The publication and a summary by Prof. Martin Müser


Publication on Physical Review Letters

The potential energy surface of a sliding interface changes shape with load

In the publication Pressure-induced friction collapse of rare-gas boundary layers sliding over metal surfaces, appeared on Physical Review Letters in 2007, M. C. Righi and M. Ferrario identify a counterintuitive behavior of rare-gas monolayers on metals that deviates from the macroscopic Amonton law.

This behaviour is dictated by quantum mechanical effects that become predominant at close surface separation and cause friction to disappear at a critical load. The challenge here is to identify other solid interfaces, suitable for practical applications, where the same effect is present.

Clelia Righi