470757 Diffusiophoretic Effects on Coffee Ring Patterns

Thursday, November 17, 2016: 8:30 AM
Union Square 23 & 24 (Hilton San Francisco Union Square)
Darrell Velegol1, Rajarshi Guha2, Farzad Mohajerani1 and Ayusman Sen3, (1)Chemical Engineering, Penn State University, University Park, PA, (2)Department of Chemical Engineering, Pennsylvania State University, University Park, PA, (3)Department of Chemistry, The Pennsylvania State University, University Park, PA

Coffee rings are a natural phenomena ubiquitous in the evaporative drying of colloidal suspensions. They are thought to be associated with only evaporation-induced capillary convection. In applications related to spray painting, coating and ink-jet printing, non-equilibrium convection-driven particle aggregation causes peripheral ring structures. The ring structure can be suppressed using higher aspect ratio particles or Marangoni convection. On the other hand, various applications require formation of strong coffee rings, while other applications want to avoid the ring structure altogether. Despite several technological advances to control the coffee ring effect, modulation from well-defined ring to completely dispersed has not been achieved successfully. Here we show both experimentally and theoretically that diffusiophoresis occurs during the evaporation of saline droplets and is efficient to concentrate or disperse the coffee rings according to the salt generated intrinsic electric fields. The coffee ring structure can be controlled by choosing various salts, whose ions have different relative diffusivities, by adjusting the particle zeta potential, or by changing the rate of evaporation. In this talk the essential physics of the process is shown, an application to particle separation is shown, and the incorporation of active colloidal motors in the coffee ring structures is explored.

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See more of this Session: Active Colloidal Systems
See more of this Group/Topical: Engineering Sciences and Fundamentals