Surface orientation of cyanobiphenyl liquid crystal monolayer and pretilt angle under various rubbing strengths

We have determined the orientational distribution function (ODF) of a liquid crystal (LC) monolayer on rubbed polyimide films by optical second-harmonic generation (SHG) using the maximum entropy method without assuming the independence of the polar and azimuthal angular distributions. The LC samples used were a homologous series of 4'-n-alkyl-4-cyanobiphenyl (nCB; n = 5-8). The rubbing strength dependence of the pretilt angle was also measured and was found to be classified into two types according to even or odd number of carbon atoms in the alkyl chain. However, we could not observe a distinct difference in ODFs of 7CB and 8CB monolayers to explain the two kinds of rubbing strength dependence of the pretilt angle.