Images and movies of crack propagation in
solid phase surfactants
J. R. Saylor
'Breaking' surfactant monolayers
Surfactant monolayers are so thin that they are essentially
two-dimensional objects. However, this does not keep them from
exhibiting phases. They are found in the gas, liquid and solid phases
just like their three-dimensional counterparts. Solid-phase
monolayers, like 3D solid-phase objects, can break or fracture. The
following is a sequence of images showing the propagation of a crack
across a solid phase monolayer. Movies of these events follow. In
these three figures, we see a solid phase surfactant monolayer
(stearic acid) before, during and after crack propagation. The time
indicated beneath each image is with respect to the moment of crack
formation. The solid phase monolayer is located on the surface of an
air/water interface, with the air initially blowing at 2 m/s over the
water surface (from top to bottom). Just before crack formation, the
air speed has been increased to 4 m/s. This exceeds the tensile
strength of the monolayer, and the crack forms.
The following movies show this fracturing process in action. At the
beginning of each movie, nothing much is happening. This is because
the solid phase monolayer is protecting the water from the air motion.
About halfway through the movie the monolayer fractures. Note how the
water suddenly moves in a very vigorous fashion as the solid-phase
monolayer is removed and the water is suddenly exposed to the wind.
In the following movie, a piece of an already fractured monolayer
breaks free and is blown downstream. We have called this a "calving
event" because it looks so much like the formation of ice bergs.
BIG
(fracture occurs at 2 min, 15 sec) 
BIG
(fracture occurs at 1 min, 6 sec)
IR movie of a calving
event.