We report a time-resolved study of the dynamics associated with the slow compaction of a granular column submitted to thermal cycles. The column height displays a complex behavior: for a large amplitude of the temperature cycles, the granular column settles continuously, experiencing a small settling at each cycle. By contrast, for a small-enough amplitude, the column exhibits a discontinuous and intermittent activity: successive collapses are separated by quiescent periods whose duration is exponentially distributed. We then discuss potential mechanisms which would account for both the compaction and the transition at finite amplitude.

We use a surface force apparatus to measure the forces exerted between cobalt surfaces by a n-decane liquid bridge formed by capillary condensation. The solid surfaces are wetted by the liquid and have an average roughness of 2 nm. When the sphere moves toward the plane, the liquid bridge forms by coalescence of two wetting films coating the surfaces. The static attractive force exerted by the liquid bridge is well described by file macroscopic theory of capillarity down to curvature radii of 8 nm. We present preliminary results on the viscous damping induced by the liquid bridge.

Aging behaviour is an important effect in the friction properties of solid surfaces. In this paper we investigate the temporal evolution of the static properties of a granular medium by studying the aging over time of the maximum stability angle of submillimetric glass beads. We report the effect of several parameters on these aging properties, such as the wear on the beads, the stress during the resting period, and the humidity content of the atmosphere. Aging effects in an ethanol atmosphere are also studied. These experimental results are discussed at the end of the paper.