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

Abstract

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 \ensuremath{\lambda} between the two phases. Its value, averaged over the contour of a seed, is (5\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ erg/cm at 20 \ifmmode^\circ\else\textdegree\fi{}C. It decreases with temperature and when stearic acid impurities are added to the monolayer. We also discuss the anisotropy of \ensuremath{\lambda} in the frame of a model based on dipolar electric interactions between molecules.