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International Center for Materials Nanoarchitectonics (WPI-MANA)

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[[Research Highlights Vol.48] Origins of Macroscopic Friction Linked to Energy Landscape on the Nanoscale](https://mdr.nims.go.jp/datasets/2f660b07-6778-45d5-9812-714daee28c4e)

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2022/03/31 16:28 Origins of Macroscopic Friction Linked to Energy Landscape on the Nanoscale| MANAhttps://www.nims.go.jp/mana/research/highlights/vol48.html 1/2Previous  Index  NextResearch Highlights[Vol. 48]Origins of Macroscopic Friction Linked to Energy Landscape on the Nanoscale19 Mar, 2019Figure: Structure of muscovite mica and considered sliding directions.Everybody is familiar with friction — the phenomenon plays an important role in our daily lives.Yet, although phenomenological laws exist that describe friction on the macroscale, a detailedunderstanding of the processes involved on the microscale is lacking. Now, Hiroshi Sakuma andShigeru Suehara (the International Center for Materials Nanoarchitectonics, National Institute forMaterials Science, Tsukuba, Japan) with their colleagues have studied friction forces in mica, boththeoretically and experimentally, and have found the origin of molecular friction in this system.Mica, a naturally laminated aluminosilicate material, should be one of the most common mineralsat the earth’s surface. It typically consists of AlO6 ‘octahedral’ sheets sandwiched between‘tetrahedral’ sheets of SiO4 and AlO4. (Octahedral and tetrahedral refer to the arrangements of thealuminium, oxygen and silicon atoms within the layers.) In between layers are potassium atoms.They focused on difference between sliding paths (directions along which a force was exerted)parallel to the main crystallographic cleavage planes.The scientists considered the energy change when applying a force to the top layer — in otherwords, when trying to pull away the layer — in each of different six directions as shown in Figure.Using a numerical technique called density functional theory, they calculated the increase (ordecrease) in energy as a function of the displacement vector by which the plane was shifted.Combining the results for all six pulling paths resulted in a potential energy surface (PES); thehttps://www.nims.go.jp/mana/research/highlights/vol47.htmlhttps://www.nims.go.jp/mana/research/highlights/index.htmlhttps://www.nims.go.jp/mana/research/highlights/vol49.html2022/03/31 16:28 Origins of Macroscopic Friction Linked to Energy Landscape on the Nanoscale| MANAhttps://www.nims.go.jp/mana/research/highlights/vol48.html 2/2height of the surface corresponds to the energy it takes to displace the top layer away from itsorigin to the new position.The research team then performed experiments, to see whether the observed trends are indeedobserved. They applied shear stresses in mica (parallel displacements within the material andsliding along path 4) up to forces corresponding to a pressure of 60 megapascal. Their mainfinding was that these stresses exhibited larger than those of predicted stresses by the numericaltechniques. Ultimately, this means that molecular-scale friction does not simply scale up to themacroscopic level.Careful observation of the recovered mica samples revealed that the presence of wear particles onthe sliding plane. This wear particles would randomize the crystallographic sliding direction by theircoincidental rotation. This means that the friction occurred along various crystallographic slidingdirections. The shear stress predicted by in-plane averaging of the numerical techniques wasquantitatively consistent with the experimental results.The results of Sakuma, Suehara, and their colleagues help to better understand the nature offriction in layered materials, and to make comparisons between them. Quoting the scientists: “...the difference of PES among sheet-structure minerals can be a clue for understanding thedifference of friction coefficients that are critical for the strength of natural faults.”Reference“What is the origin of macroscopic friction?”Hiroshi Sakuma, Kenji Kawai, Ikuo Katayama, and Shigeru SueharaJournal : Science Advances 4, eaav2268 (2018)DOI : 10.1126/sciadv.aav2268AffiliationsInternational Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for MaterialsScience (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, JapanContact informationInternational Center for Materials Nanoarchitectonics(WPI-MANA)National Institute for Materials Science1-1 Namiki, Tsukuba, Ibaraki 305-0044 JapanPhone: +81-29-860-4710E-mail: mana-pr[AT]ml.nims.go.jphttps://samurai.nims.go.jp/profiles/suehara_shigeru?locale=enhttps://advances.sciencemag.org/content/4/12/eaav2268