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DY: Fachverband Dynamik und Statistische Physik

DY 21: Granular Matter / Contact Dynamics

DY 21.8: Vortrag

Mittwoch, 13. März 2013, 17:00–17:15, H47

Surface melting of wet granular matter in two dimensions — Christopher May, Ingo Rehberg, and •Kai Huang — Experimentalphysik V, Universität Bayreuth, 95440 Bayreuth, Germany

Surface melting has been a topic of interest since Michael Faraday's observations on regelation, welding of two blocks of ice after contact below 0 degree. From the qualitative idea of surface energy reduction to quantitative experimental tests, it becomes clear nowadays that melting is a continuous process that tends to start from the free surface.

In the present investigation, we address the `melting' scenario of a monolayer of wet glass beads under horizontally swirling motion experimentally. Due to the cohesion arising from the formation of capillary bridges between adjacent particles, the particles initially form a crystalline structure at moderate driving. As the strength of driving increases, this structure is found to melt with two steps: A reshaping into a circular shape while keeping a locally hexagonal structure, followed by a melting from the surface. Quantitative characterizations on local packing density and bond orientational order parameters both reveal a critical swirling frequency for the start of surface melting, which can be rationalized with a balance between the energy injection and the barrier for the structure change of surface particles.