Buckling of Langmuir Monolayers

We show that under compression on a Langmuir trough, a surfactant monolayer may have a mechanical instability similar to the buckling instability of a beam or a plate. In the buckled state, the wavelength of the surface undulations is the capillary length resulting from the balance between gravity and curvature energy and is in the range of 104 A. For the specific example of block copolymer surfactants, we discuss the competition between the buckling instability and dissolution of the surfactant in the supporting liquid.