COMPARISON OF THE ANCHORING OF NEMATIC LIQUID-CRYSTALS ON SELF-ASSEMBLED MONOLAYERS FORMED FROM SEMIFLUORINATED THIOLS AND ALKANETHIOLS

The anchoring of nematic liquid crystals on self-assembled monolayers (SAMs) formed by the chemisorption of semifluorinated thiols or alkane thiols on gold is compared and contrasted. The planar anchoring of 4-n -pentyl-4'-cyanobiphenyl (5CB) observed in the past on SAMs formed fro m alkanethiols is also observed on SAMs formed from semifluorinated th iols. The azimuthal anchoring of 5CB, however, differs on these two ty pes of surfaces: nematic 5CB anchored on SAMs formed from alkanethiols has a grainy appearance due to the formation of domains with sizes <1 0 mu m whereas 5CB forms large domains (similar to 100 mu m) with diff use branches emerging from defects of strength 1/2 when anchored on SA Ms formed from semifluorinated thiols. Mixed (two-component) SAMs form ed from either short and long semifluorinated thiols or short and long alkanethiols cause homeotropic anchoring of 5CB. We discuss these res ults in light of the known differences in the structure of SAMs formed from alkanethiols and semifluorinated thiols, i.e. the tilt of the ch ains and conformational freedom (flexibility) of the chains within the se SAMs.