Spontaneous self-assembly of partially fluorinated bolaamphiphiles into ordered layered structures.

Abstract

We developed a simple method for preparation of well-defined films of X-, T- and anchor-shaped bolaamphiphiles. The compounds were judiciously chosen to investigate the influence of the general molecular structure on the self-assembly properties. Precisely calculated (on the basis of Langmuir π(A) isotherms) volumes of chloroform solutions of the compounds of known concentrations were spread (drop-casted) directly onto the surface of water or silicon wafer. During the solvent evaporation, regular thin films were spontaneously formed. With use of the drop-casting (DC) method, films of thickness of up to three molecular layers could be obtained. X-ray reflectivity (XRR) measurements gave insight into arrangement of the molecules within the films. Different models of molecular organisation in the films were confronted with the experimental results. Advanced fitting procedures allowed for precise determination of the structure of the films. Comparison of films of different compounds obtained using different methods (Langmuir-Blodgett, DC) allowed for a deeper insight into the process of self-assembly, providing guidelines for designing functional molecules spontaneously forming thin, regular films. The proposed DC procedure is a novel alternative to broadly used self-assembled monolayers (SAMs). Unlike SAMs, our method does not require specific molecule-surface interactions and allows formation of films thicker than a monolayer.