title: Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves.
abstract: 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.
authors.affiliation: Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: M
authors.initials: M
authors.lastname: Hiraiwa
authors.affiliation: Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: M
authors.initials: M
authors.lastname: Abi Ghanem
authors.affiliation: Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Wallen
authors.affiliation: Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: A
authors.initials: A
authors.lastname: Khanolkar
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Maznev
authors.affiliation: Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195, USA.
authors.forename: N
authors.initials: N
authors.lastname: Boechler