Particles rafts, formed as two dimensional assemblies of floating particles, are prone to develop highly non linear response under compression, significantly altering the capillary properties of the host fluid interface. It has been previously shown that particle-wall friction induces Janssen-like exponential screening of surface stresses. Here we map the transition to this friction-dominated jammed state and explain the progressive development of the screening profile in terms of friction mobilization. The analysis of the elastic deformation of ring sensors distributed along the raft surface reveals a stress-screening distance that is dramatically smaller than Janssen’s prediction. A simple mathematical analysis indicates that such enhanced screening can be attributed to the presence of a gradient of rigidity induced by the localized compaction of rafts of large aspect ratio.
Figure 1- Soft polymeric rings serve as local pressure sensors and reveal the internal stress distribution of the granular raft. The classical Janssen’s hypothesis is not sufficient to properly explain raft mechanics.
- Friction mobilization and gradient-induced enhanced Janssen’s screening in confined granular rafts
O. Saavedra, H. Elettro & F. Melo
Submitted to Physical Review Letters (2017)