Planar anchoring of nematic 4-n-pentyl-4'-cyanobiphenyl on self-assembled monolayers formed from alkanethiols on gold

We report measurements of planar anchoring of nematic 4-n-pentyl-4'-cyanobiphenyl (5CB) on self-assembled monolayers (SAMs) fanned from CH3(CH2)(m)SH (7 less than or equal to m less than or equal to 17) on films of gold (prepared without oblique deposition) by using reflection interferometry. The anchoring observed contrasts with past reports of homeotropic anchoring of 5CB by surfaces, such as monolayers formed from octadecyltrichlorosilane on silica, with energies as low as alkanethiols on gold (19 mN/m). The anisotropic dispersion force acting between 5CB and gold was calculated to favor planar anchoring of 5CB on SAMs formed from CH3(CH2)(15)SH by similar to 0.1 mN/m, and can, therefore, override self-interactions of 5CB that lead to homeotropic anchoring. Electric field-induced Freederiksz transitions of 5CB supported on bare gold, and on SAMs formed from CH3(CH2)(15)SH on gold, confirm weaker (planar) anchoring of 5CB on SAMs on gold as compared to bare gold. (C) 1996 American Institute of Physics.