  The maximum pressure a two-dimensional surfactant monolayer is able to
withstand is limited by the collapse instability towards formation of
three-dimensional material. We propose a new description for reversible
collapse based on a mathematical analogy between the formation of folds in
surfactant monolayers and the formation of Griffith Cracks in solid plates
under stress. The description, which is tested in a combined microscopy and
rheology study of the collapse of a single-phase Langmuir monolayer of
2-hydroxy-tetracosanoic acid (2-OH TCA), provides a connection between the
in-plane rheology of LM's and reversible folding.
