First measurement of the liquid-solid line energy in a Langmuir monolayer

We observe the homogeneous 2D nucleation of solid anisotropic domains from a liquid phase in an amphiphilic nitrobenzoxadiazole stearic acid monolayer. The nucleation rate decreases exponentially with the inverse of the excess surface pressure. We measure the line energy λ between the two phases. Its value, averaged over the contour of a seed, is (5±0.5)×${10}^{\mathrm{-}7}$ erg/cm at 20 °C. It decreases with temperature and when stearic acid impurities are added to the monolayer. We also discuss the anisotropy of λ in the frame of a model based on dipolar electric interactions between molecules.