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Science 13 April 2001:
Vol. 292. no. 5515, pp. 265 - 267
DOI: 10.1126/science.1059175
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Reports

Using Selective Withdrawal to Coat Microparticles

Itai Cohen,1 Hui Li,2 James L. Hougland,2 Milan Mrksich,2 Sidney R. Nagel1

We report a method that uses the process of selective withdrawal of one fluid through a second immiscible fluid to coat small particles with polymer films. Fluid is withdrawn through a tube with its orifice slightly above a water-oil interface. Upon increasing the flow rate, there is a transition from a state where only oil is withdrawn to a state where the water, containing the particles to be coated and appropriate prepolymer reagents, is entrained in a thin spout along with the oil. The entrained particles eventually cause the spout interface to break, producing a thin coat of controllable thickness around each particle, which can be subsequently polymerized using chemical reagents, light, or heat. This method allows flexibility in the chemical composition and thickness of the conformal coatings.

1 James Frank Institute and Department of Physics,
2 Department of Chemistry, University of Chicago, Chicago, IL 60637, USA.

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