Building
designed granular towers one drop at a time
Julien
Chopin and Arshad Kudrolli
Phys. Rev. Lett. 107, 208304 (2011). Editor's Suggestion
Department of Physics, Clark University, Worcester, Massachusetts 01610, USA
We show an unprecedented variety of smooth symmetric, corrugated,
zig-zag shaped slender structures that can be observed by simply
dripping a mixture of sand and water on a liquid absorbing surface
such as a dry bed of sand or blotting paper. The various shapes are in
contrast with the liquid drops which can splash, spread or bounce upon
hitting a surface. Successive drops are observed to freeze rapidly
upon impact due to the drainage of a small fraction of liquid,
literally stacking on top of each other into surprisingly slender
structures named granular towers. Further, twisted pagoda dome-like
structures are observed by increasing the flux into the jetting
regime. We show that the towers are held together because of capillary
and friction forces, and the shape of the towers depends on a subtle
balance between dripping frequency, density of grains, and impact
speed. Besides applications in surface patterning, this tower building
technique may be a new and easy way to probe the flow properties of
dense granular suspensions using the shape of the tower.
Images and movies of
the towers follow.
A.
List of Movies
Movie S1: Movie of granular suspension (GS-1)
spreading on a glass slide coated with a layer of glass beads. The scale bar is
5mm. Flux rate Q=4.77mL/min. Image acquisition rate 20 frames/s. The spreading
of the suspension occurs in two stages: first, after impact, the puddle
increases in volume but the wetting front remains roughly immobile leading to a
rapid increase of the thickness. Then, the wetting front expands leading to a slow
decrease of the thickness of the puddle before the next drop arrives.
Movie S2: A movie (3frames/s) of a 150mm high granular
tower formed by dripping GS-1 at Q=2.86mL/min.
Movie S3: Movie (8400frames/s) illustrates the rapid
drainage of excess liquid from a drop after impact. The scale bar is 3mm.
Movie S4: Montage of four granular towers obtained
by dripping GS-3 at Q=2.86 5mL/min, 9.545mL/min, 19.15mL/min and 47.5mL/min (50
frames/s). The picture is approximately
70mm high.
Movie S5: Chiral pagoda-like structure obtained by
dripping GS-2 at Q=95.4mL/min (40frames/s). The picture height is approximately
40mm
Movie S6: Falling drop with a volume fraction (left)
φ=58% and (right) φ=55%. The nozzle with a 2.35mm inner diameter can
be seen at top for scale. A satellite drop can be seen on the right (movies S7,
frame rate 800img/s).
Movie S7: Movie illustrates the flow of water
through the tower obtained by dripping GS-1 at Q=2.86mL/min. A drop of the same
suspension containing a dye (methylene blue) was placed manually using another
syringe when the dripping was paused briefly. The flow of water through the
tower is thus made visible upon resumption (40frames/s).
Contact:
Arshad Kudrolli
akudrolli@clarku.edu
Department of Physics
Clark University
Worcester, MA 01610
Last updated November 25, 2011