Orientation mechanisms for small solutes in the nematic liquid crystal 5CB-α,β-d₄

Abstract

Two principal mechanisms are shown to be important for the orientational order of small solute molecules in the nematic liquid crystal 4-(α,β-d ₄-n-pentyl)-4'-cyanobiphenyl (5CB-α,β-d ₄). The interaction between the mean electric field gradient due to the liquid crystal and the molecular quadrupole moment of the solute is particularly important for small molecules such as hydrogen. For larger solutes, like 1,3,5-trichlorobenzene, the short-range interactions which are proportional to the size and shape of the solute are important. A model which takes both mechanisms into account is used to calculate solute molecular order parameters. Excellent agreement between the calculated parameters and those obtained from N.M.R. measurements is found.