STRUCTURE OF TRANS-4-(TRANS-4-NORMAL-PENTYLCYCLOHEXYL)CYCLOHEXYLCARBONITRILE (CCH5) IN THE ISOTROPIC AND NEMATIC PHASES - A COMPUTER-SIMULATION STUDY

We have studied the single particle structural properties of the nematogen trans-4-(trans-4-n-pentylcyclohexyl)cyclohexylcarbonitrile (CCH5) by molecular dynamics simulation using realistic atom-atom potentials. On going from the isotropic phase at 390 K to the nematic phase at 350 K, the molecules become significantly longer and thinner, as indicated by the equivalent molecular moment-of-inertia spheroid and the distribution of trans and gauche bonds. This change is only partly accounted for by the lowering of the temperature, there being a significant quenching effect due to the change in the molecular environment. This quenching effect is also apparent in the distribution of molecular shapes seen in molecular width-breadth contour maps. In the nematic phase, at 350 K, the distributions of alkyl tail bond orientations with respect to the director show a pronounced odd even effect, with peaks in the distributions occurring alternately parallel to, and at an angle to, the director.