Molecular order in self-assembled multilayers of stearic acid

Self-assembled multilayers of stearic acid were obtained by evaporating a drop of stearic acid dissolved in organic solvent onto a cleaned glass slide. X-ray diffraction and scanning force microscopy (SFM) were used to determine the bulk structure and to study the surface at molecular level. In samples prepared from decane solution, at least two crystalline forms (A + C and B + C, but seldom A + B + C) coexist and the molecules at the surface appear arranged according to a two-dimensional non-centered rectangular lattice. After annealing of the samples at 80 degrees C (slightly above the melting point of stearic acid), the C-form exists singly: accordingly, the molecular arrangement at the surface reverts to an hexagonal pattern. A periodic buckling superstructure is also observed by SFM in non-annealed samples. Moreover, X-ray diffraction results indicate that recrystallization processes occur.