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Coffee ring revelations in California

2007 Ig Nobel Physics Prize winner L. Mahadevan and colleagues gave a talk yesterday about the physics of coffee rings. This happened at a meeting of the American Physical Society Division of Fluid Mechanics, held in Long Beach, California. The meeting notes give a bit of detail:

Abstract: RU.00007 : Coffee ring deposition in bands

Shreyas Mandre (Brown University)
Ning Wu (Colorado School of Mines)
Joanna Aizenberg (Harvard University)
Lakshminarayanan Mahadevan (Harvard University)

Microscopic particles suspended in a liquid are transported and deposited at a contact line, as the contact line recedes due to evaporation. A particle layer of uniform thickness is deposited if the particle concentration is above a threshold; below this threshold the deposit forms periodic bands oriented parallel to the contact line. We present a model for the formation of these bands based on evaporation leading to the breakup of the thin liquid film near the contact line. The threshold results from a competition between evaporation speed and deposition speed. Using this model, we predict the thickness and length of the bands, making the control of patterned deposition possible.

Mahadevan and colleague Enrique Cerda Villablanca shared the Ig Nobel Prize for investigating how sheets become wrinkled.

(Thanks to investigator Ian Mansfield for bringing this to our attention.)

Improbable Research