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