DriveAFM for polymer chemistry

This application note concerns AFM studies of self-assembled semi-fluorinated alkanes on Silicon, HOPG and MoS₂ substrates. These molecules are formed of covalently linked sequences of -CF₂- and -CH₂- groups with -CF₃ and -CH₃ terminals, respectively. Their molecular composition F(CF₂)_n(CH₂)_mH can be connoted as FnHm (Figure 1a). The compounds consist of two incompatible subunits that segregate into distinct domains like block copolymers, but without polydispersity in molecular weight. Structural ordering of such compounds is controlled by the strong incompatibility of the constituting segments, and also by the fact that the van der Waals cross-section of the flexible hydrocarbon segment is 25-30% smaller than that of the rigid helical perfluorinated segment, (Figure 1b). X-ray reflectivity studies of F14H20 films suggested that the fluorinated chains are oriented normal to the surface layer and where the alkyl segments are tilted with an angle between the two segments.