Oriented growth of n-alkanes crystals on nanostructured poly(tetrafluoroethylene) substrates

The growth of n-alkane (CnH2n+2) crystals on poly(tetrafluoroethylene) substrates (PIA) obtained by the friction-transfer method was studied by optical microscopy and grazing incidence x-ray diffraction. The experiments performed on a series of molecules ranging from n=21 to n=33 reveal the existence of a preferred contact plane with the PIA substrate corresponding to a minimum in lattice mismatch between the two crystallographic systems. Independently of the chain length, the n-alkane crystals tend to orient with their (200) planes parallel to the substrate, the molecular axis being preferentially aligned along the friction direction of the PTFE substrate. In our study, we demonstrate that the pathways (i.e., the orientation mechanisms) strongly influence the observed morphology in the low temperature phase.