Atomic force microscope evidence for the existence of smecticlike surface layers in the isotropic phase of a nematic liquid crystal

Using a temperature controlled atomic force microscope we have observed presmectic layering in the isotropic phase of 4-cyano-4^'-n-octylbiphenyl (8CB) on silanated glass. The first molecular layer shows a smecticlike compressibility modulus of B≈10⁷ N/m² and is stable more than 20 K beyond the bulk clearing point. It is followed by a presmectic modulation that increases when cooling towards the isotropic-nematic transition. In the bulk isotropic phase, the layers cover approximately 70% of the glass surface, indicating a clusterlike organization.