Archives de la cat├ęgorie: Wet Granular Materials

Wet Granular Materials

Building Designed Granular Towers One Drop at a Time

Tower
A dense granular suspension dripping on an imbibing surface is observed to give rise to slender mechanically stable structures that we call granular towers. Successive drops of grain-liquid mixtures are shown to solidify rapidly upon contact with a liquid absorbing substrate. A balance of excess liquid flux and drainage rate is found to capture the typical growth and height of the towers. The tower width is captured by the Weber number, which gives the relative importance of inertia and capillary forces. Various symmetric, smooth, corrugated, zigzag, and chiral structures are observed by varying the impact velocity and the flux rate from droplet to jetting regime.

Reference :
Building Designed Granular Towers One Drop at a Time, J. Chopin and A. Kudrolli, Phys. Rev. Lett. 107, 208304 (2011)

Wet Granular Materials

Pearling and arching instabilities of a granular suspension on a superabsorbing surface

Arches

We show that a granular suspension, composed of particles immersed in a liquid, can form pearls, hooks, and arches when deposited from a nozzle onto a translating substrate that acts as a liquid super-absorber. The removal of the liquid induces a rapid pinning of the contact line leading to mechanically stable structures that are held together by capillary adhesion with shapes that depend on the relative solidification rate. Pearls or hooks form depending on whether the suspension snaps off before or after coming into contact with the substrate. A cylindrical thread with a near circular cross-section and various undulatory structures forms if solidification occurs prior to snap-off. In particular, when the jet solidifies before coming into contact with the substrate, it folds periodically, resulting in arches with a span length determined by the deposition flux and the substrate speed. Period doubling and meandering are observed leading to further structures with vertical and horizontal ripples when the deposition flux is increased.

Reference :
Pearling and arching instabilities of a granular suspension on a superabsorbing surface ,
J. Chopin and A. Kudrolli, Soft Matter 11, 659 (2015)