liquid al surface density profile f.d. di tolla, phd thesis (1996)
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Liquid Al surface density profile
F.D. Di Tolla, PhD Thesis (1996)
Density profile for gas & liquid in pore
Walton and Quirke, Chem. Phys. Lett. 129, 382 (1986).
Turbulent nature of liquid surface
http://physics.weber.edu/schroeder/software/MDApplet.htmlhttp://physics.weber.edu/schroeder/software/demos/MDv0.html
Molecular Dynamics Applet
Surface reconstruction
Si (111)Au (100)
Different surfaces within a crystal
Low index surfaces for a face-centered cubic (fcc) crystal
Surface reconstruction
fcc
Surface reconstruction
Si (111)
Adsorbate superlattices
Surface tension from cohesive forces
Water-walking insects
Soap bubbles
Soap bubbles
Giant soap films
http://maartenrutgers.org/ 1999 APS meeting
Experiment to define surface tension
Pressure difference across curved surface
Temperature Dependence of Surface Tension
THIN LIQUID FILMS
• thin liquid films occur in everyday life – adhesives (superglue)– lubricants (on cornea of eye, engine piston)– spray coatings (paint, herbicides, fibers)– printing (ink on transparency or tape)– soap bubbles & films– foams (shaving cream, cappuccino)
– water films (water spotting, hydroplaning)
stabilitydesirable/essential
stabilityundesirable
DEWETTING OF POLYMER FILMS
• PS films on Si dewet at elevated temperatures– form polygonal patterns of PS droplets [G. Reiter, PRL 68, 75 (1992)]
• same patterns observed for dewetting of PS on PMMA[e.g. S. Qu et al., Macromolecules 30, 3640 (1997)]
PS/Si PS/PMMA
Contact angle
glg
q
gslgsg
gsg – gsl – glg cos q = 0
liquid
solid
gas
Inspired by Nature
– lotus leaf– symbol of purity– nature’s self-cleaning surface
– mimic microstructure on surface
[D. Quéré, Nature Mater. (2002)]
Cheerios effect
coined by Jearl Walker, Flying Circus of Physics
Cheerios effect
can also lead to formation of bubble rafts
[Vella & Mahadevan, Am. J. Phys. (2005)]
Sphere at liquid-gas interface
Waterlily leaf beetle larva
Hu & Bush, Nature 437, 733 (2005).
Capillary origami [Py et al., PRL (2007)]
Capillary force on AFM tip
Fcap = 2pRg (cos q1 + cos q2)
Capillary force on AFM tip
[Sirghi et al., Langmuir (2001)]
Force Spectroscopy in AFM
• forces between AFM tip and a mica surface in air and water
• measurement in air shows large adhesive force due to capillary effect
• immersion in water almost completely eliminates capillary forces and adhesion