Even-odd effects in liquid crystal dimers with flexible spacers: a test of the rotational isomeric state approximation?

In this work we analyse the consequences of relaxing the rotational isomeric state (RIS) approximation in predicting the transitional properties of nematogenic systems formed by two mesogenic moieties linked by a flexible spacer, as in the homologous series of α,ω-bis(4′-cyanobiphenyl-4-yl)alkanes and α,ω-bis(4′-cyanobiphenyl-4-yloxy)alkanes, generically referred to as CB dimers. Comparison is made therefore between predictions of the nematic-isotropic transition temperatures, entropy changes, and order parameters obtained from the RIS model, and those by taking into account the full distribution of torsional angles. The continuous model predicts a damping of the even-odd effects for long chain systems, with entropy changes and order parameters at the nematic-isotropic transition tending to those of the corresponding monomers.