The anchoring orientation of different liquid crystals in contact with poly(tetrafluoroethylene) (PTFE) treated surfaces is determined by means of optical interferometry. The anchoring is found to be planar for all the compounds tested, MBBA, 2OO6, 5CB and 7BPI, consisting of polar and non-polar molecules, in the nematic or smectic A phase. This result is consistent with the non-polar nature of PTFE, which is only sensitive to London-like interactions