Patterning of Small Particles

1
Patterning of Small ParticlesSurface Tension
vs. Temperature

• Lu Zou
• Group meeting
• Jul. 10, 06
• Ref Nguyen, V.X. Stebe, K. J. PRL, Vol. 88,
  16, 164501, 2002

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

3
Coffee Ring Benard Cells

• 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)

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

4
Why a drying drop forms a Coffee Ring?
Ref http//mrsec.uchicago.edu/ Nuggets/Coffee/
5
Benard Convection
physics.ucsd.edu/was-daedalus/ convection/rb.html
6
A Droplet with Surfactant
Pentadecanoic Acid (PDA) Dyed by NBD-HDA
HCl 0.01 microspheres (D 0.8um)
Modified SiO2 Substrate Contact angle for water
is 50o /- 3o
7
Isotherm of PDA w/ NBD-HDA
8
For the LC-LE State
9
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.
10
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.