Paper Number
AD10
Session
Rheology of Active Matter and Directed Systems
Title
Flowing sand uphill: Granular dynamics of magnetically-driven particle rotation
Presentation Date and Time
October 12, 2022 (Wednesday) 5:05
Track / Room
Track 4 / Michigan AB
Authors
- Gilchrist, James F. (Lehigh University, Chemical and Biomolecular Engineering)
- Wilson-Whitford, Samuel (Lehigh University, Department of Chemical and Biomolecular Engineering)
- Gao, Jinghui (Lehigh University, Department of Chemical and Biomolecular Engineering)
- Buckley, William (Lehigh University, Department of Chemical and Biomolecular Engineering)
Author and Affiliation Lines
James F. Gilchrist, Samuel Wilson-Whitford, Jinghui Gao and William Buckley
Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA 18015
Speaker / Presenter
Gilchrist, James F.
Keywords
experimental methods; theoretical methods; active matter; directed systems; flow-induced instabilities; jammed systems; suspensions
Text of Abstract
Gravity-driven granular flows, commonly found in nature in the form of avalanches and landslides and industrial processing, have long piqued the interest of scientists and engineers. Their actuation simplicity and response complexity have designated them as a cornerstone system of study within the soft matter and complex systems communities. Heap formation is a typical behavior of poured granular systems. With continuous addition of a granular material, such as sand, to a flat surface, as a heap forms a continuous gravity driven boundary flow can be observed in which grains are transported from an uphill to a downhill position. The heap itself grows as grains are transferred from the boundary layer to the underlying static heap. The dissipation of potential energy through frictional particle-particle and hydrodynamic particle-fluid interactions within the boundary layer shear flow leads to a fundamental slope angle, known as the angle of repose and the kinematics of the boundary layer itself have been well-documented through granular rheology of these inertial systems.
What has not previously been explored is the behavior of granular systems where shear is introduced to the system through torque applied directly to the particles themselves. In this work, a granular system of 50 micron ferromagnetic Janus particles is prepared. These responsive Janus particles are rotated through the application of magnetic torque by an external rotating magnetic field resulting in uphill granular heaping which for all purposes demonstrates quintessential granular behavior, such as boundary layer flow, but against gravity, giving rise to a negative angle of repose (downhill to uphill). It is proposed that the behavior is governed frictional control as a direct result of the magnetic field strength. These observations elucidate a whole new way to observe granular systems and have a significant impact on the way in which granular systems could be applied.