Nucleation and oriented growth of aromatic crystals on friction-transferred poly(tetrafluoroethylene) layers

The oriented growth of p-nitroaniline and hydroquinone deposited from the vapor phase on monooriented thin films of poly(tetrafluoroethylene) (PTFE) prepared by friction transfer is investigated by grazing incidence X-ray diffraction and polarized FTIR spectroscopy. Due to the formation of two-dimensional hydrogen-bonded networks, both aromatic compounds crystallize with a layered structure. p-Nitroaniline is found to contact the (100)(PTFE) surface with its (101)(PNA) crystallographic plane which is parallel to the hydrogen-bonded sheet. A similar PTFE/hydrogen-bonded sheet interface was never observed for gamma-hydroquinone crystals vacuum deposited under similar experimental conditions. In fact, hydroquinone orients on PTFE with a (110)(HYD) or (1 (1) over bar 0)(HYD) contact plane. Reconstruction of the PTFE substrate at the substrate/deposit interface is invoked as a tentative explanation of the difference in orientational behavior of these two organic compounds.