Reminiscent of children building castles at the beach by dripping wet sand from their fist, researchers in Massachusetts have created their own slender towers by dripping a suspension of glass beads in a water–glycerine mixture over a granular surface.
Julien Chopin and Arshad Kudrolli at Clark University in Worcester used a high-speed camera to reveal the mechanics of the surprisingly cohesive structures (pictured). They found that they could control the shape and height of the tower by adjusting the speed of the dripping and the volume fraction of the beads in the suspension.
The researchers suggest that the technique could be an alternative route to surface patterning and three-dimensional printing.
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Towers grow by drips and drops. Nature 479, 449 (2011). https://doi.org/10.1038/479449a