07/10/06 Group Meeting 1

Patterning of Small Particles&Surface Tension vs. TemperatureLu Zou

Group meeting

Jul. 10, ’06

Ref: Nguyen, V.X.; Stebe, K. J.; PRL, Vol. 88, 16, 164501, 2002

07/10/06 Group Meeting 2

Patterning of Nanoparticles

A drop containing finely divided particles Evaporation Particles are deposited in macroscopic

patterns Interactions among the particles can be

exploited to create local order

07/10/06 Group Meeting 3

“Coffee Ring” & “Benard Cells”

R. D. Deegan and others 1997. "Capillary flow as the cause of ring stains from dried liquid drops", Nature, volume 389, pp827-829

M. Maillard, L. Motte, M.-P. Pileni ; Rings and Hexagons Made of Nanocrystals, Adv. Mater. 2001, 13, 200-204

(or say, periodic flow patterns, Hexagon patterns)

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Why a drying drop forms a “Coffee Ring”?

Ref: http://mrsec.uchicago.edu/ Nuggets/Coffee/

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Benard Convection

physics.ucsd.edu/was-daedalus/ convection/rb.html

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A Droplet with Surfactant

HCl + 0.01% microspheres (D =

0.8um)

Pentadecanoic Acid (PDA)

Dyed by NBD-HDA

Modified SiO2 Substrate

Contact angle for water is 50o +/- 3o

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Isotherm of PDA w/ NBD-HDA

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For the LC-LE State

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For the LE State

When the interface is in LC-LE coexistence, the Benard convection is present, even though the concentration of the surfactant is significant.

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2 Possible Explanation

In the LE-LC coexistence regime, compositional Marangoni stresses are weak.

In the LE-LC coexistence regime, temperature-driven Marangoni stresses are strong.