MOLECULAR ORDER IN SELF-ASSEMBLED MULTILAYERS OF STEARIC-ACID

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