Thermostatistics of a single particle on a granular dimer lattice: influence of defects.

We study the thermostatistical fluctuations of a single Delrin monomer on a granular lattice of dimer particles using both experiment and simulation. The goal is to examine the collision frequency, energy injection, and sidewall effects on a single second-layer particle in a bilayer granular gas experiment. Non-Gaussian velocity statistics are observed for the single particle of the top layer and result from the presence of defects in the first layer. These deviations are not directly due to the presence of the boundary wall, since the form of velocity distributions is quite spatially homogeneous, but are the consequence of the presence of a few mobile defects in the first layer.

Forced detachment of immersed elastic rubber beads.

We investigate the strength of adhesion and the dynamics of detachment of elastic beads (Young's modulus E approximately 1 MPa) adhering to a horizontal solid surface in a viscous liquid. The beads are initially compressed on the surface. Their unbinding is imposed by fast vertical stretching (above a certain threshold value). The decrease in the contact radius is monitored by interferential microscopy. We find that the dynamics of detachment involves three steps: (i) fast elastic decompression, (ii) slow adhesive detachment, and (iii) catastrophic rupture. They can be interpreted by a transfer of the Johnson Kendall Roberts (JKR) energy toward viscous losses in the liquid wedge, near the rubber/solid/liquid (R/S/L) contact line.