Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves

• Main Authors: Hiraiwa, M. (Author), Abi Ghanem, M. (Author), Wallen, S. P (Author), Khanolkar, A. (Author), Boechler, N. (Author), Maznev, Alexei (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Chemistry (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2016-05-24T14:09:32Z.
• Subjects: Article
• Online Access: Get fulltext

Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks.
National Science Foundation (U.S.) (Grant CMMI-1333858)
United States. Army Research Office (Grant W911NF-15-1-0030)
University of Washington. Royalty Research Foundation
National Science Foundation (U.S.) (Grant CHE-1111557)