Figure shows snapshots from the simulations of 8OCB and 9 at times when the layers are relatively well-defined, with each molecule represented by a cylinder that corresponds to the N-O molecular vector, i.e. the relatively rigid aromatic moiety, used to determine the orientational order parameters. For 8OCB, the layers are not very well defined, as indicated also by the relatively low value of τ, and some of the layers show large ripples. By contrast, the layers of 9 are more clearly defined and flatter, with the empty regions between the layers of cylinders in this snapshot containing the cyclohexyl-C5 chains (not shown in this snapshot for clarity). Moreover, an examination of the density of layered atoms along the layer normal vector (comparable to the director) over time showed that the layers of 8OCB often formed for short periods of ca. 10-20 ns before breaking up and then reforming at other locations along the layer normal vector at later times, whereas the layers of 9 remained comparatively stable in location once formed. The structures of the phases were also assessed using pair-wise correlation functions of vectors between the C4 and C4' biphenyl atoms on all of the molecules, as shown in Figure . The radial distribution function g(r) used the centres of the biphenyl vectors, and shows liquid-like distributions with peaks at ca. 5.1 and 9.9 Å for both 8OCB and 9, corresponding to "shells" of surrounding molecules, and tending towards 1 at longer distances indicating long-range disorder; the slightly higher g(r) values for 9 than 8OCB are consistent with a slightly more ordered phase. The first-order orientational correlation functions G1(r) of the biphenyl vectors in 8OCB and 9 both show a negative peak at ca. 3-4 Å corresponding to antiparallel molecular orientations of the biphenyl units being favoured in the first shell, and a weaker positive peak at ca. 7 Å corresponding to parallel molecular orientations being favoured more weakly in the next shell (as illustrated schematically in Figure and); this observation is consistent with those reported from simulations of other related nCB and nOCB systems. The second-order orientational correlation function G2(r) used the same biphenyl reference vector, and shows a peak at ca. 5 Å indicating a very high P2 orientational order in the first shell that decreases towards values of <P2> 2 at longer distances, as expected. Taken together, the distribution functions in Figure show that the ordering behaviour of the biphenyl groups of 8OCB and 9 are similar, which suggests that the differences in smectic layer formation and stability are strongly influenced by the nature of the alkyl chains at the other ends of these molecules. The extent of layering and interdigitation of the molecules was assessed using a similar approach to that reported for 11OCB and t-Bu-11OCB. Figure shows the relative populations along the layer normal vector, z, of a selected head-group atom (C4′ biphenyl for both 8OCB and 9, as used to determine τ values) and a selected tail-group atom (the terminal carbon atom; C8 alkyl for 8OCB, and C4 cyclohexyl for 9) during a 50 ns window when the layer positions were relatively stable in each simulation box. All of the relative populations have an approximately sinusoidal form, as shown by the black lines in Figure , with the populations of the head-group and tail-group atoms being out of phase, which indicates the presence of distinct aromatic and aliphatic regions along the layer normal. The amplitude of the oscillations is low for 8OCB, illustrating the diffuse nature of the layers, and much higher for 9, showing the greater degree of nanosegregation between its aromatic and aliphatic moieties.