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8.3.2023 15:00 s.t. - Lecture hall 25.31 O0.5J
Lucio Isa: „Sliding or rolling? Characterizing single-particle contacts”
Department of Materials, ETH Zurich, Switzerland
The characterization of contact forces between particles has received increasing attention in recent years due to the role that they are believed to play in determining the rheology of dense suspensions. In particular, lateral force microscopy (LFM) has enabled measuring sliding friction at the single-particle level by measuring the torsion of an atomic force microscopy cantilever onto which a particle is glued and made to slide onto a counter-surface as a function of normal load [1]. A broad range of experimental, numerical and theoretical studies has linked the presence of sliding friction to the onset of discontinuous shear thickening in dense suspensions, making it a necessary parameter to describe their rheology [2].
However, in addition to pure sliding, particles in a fluid are also free to rotate relative to one another, but the characterization of rolling friction at the single-particle level remains practically unexplored, even though its role in shear thickening is being called into question [3,4]. Key to the measurement of rolling friction is the possibility to measure the relative rotation between particles while simultaneously measuring lateral forces as a function of normal load.
Here, I will describe an upgrade to LFM, which uses nanofabricated probes to measure sliding and rolling friction among microparticles as a function of their surface properties. The particles have fluorescent asperities, which enables tracking their rotation during LFM. I will explain the details of the technique and report results for particles of different surface roughness.
This new tool offers exciting possibilities to expand the well-established characterization of sliding friction via colloidal-probe LFM to the largely-unexplored characterization of rolling friction, as of high interested both in suspensions’ rheology and in functional coatings.
References
- C.-P. Hsu, S.N. Ramakrishna, M. Zanini, N.D. Spencer and L. Isa, Proceedings of the National Academy of Sciences, 2018, 115 (20), 5117-5122
- M. M. Denn, J. F. Morris and D. Bonn, Soft Matter, 2018,14, 170-184.
- B.M. Guy, J.A. Richards, D.J.M. Hodgson, E. Blanco and W.C.K. Poon, Physical Review Letters, 2018, 121(12), 128001.
- A. Singh, C. Ness, R. Seto, J. J. de Pablo and H. M. Jaeger, Physical Review Letters, 2020, 124, 248005.
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