The Chromonic N and M Phases

Figure 2. The structure of the chromonic N and M phases The basic structural unit of both phases is the untilted stack of molecules. The N phase is a nematic array in which these stacks lie in a more or less parallel pattern, but where there is no positional ordering. Tlie M phase is a hexagonal array of these columns. The six-fold symmetry is a result of orientational (but not positional) disorder. A schematic diagram of a localized region, as shown in (a) has only orthorhombic symmetry, but, averaged over the whole structure, each column actually lies in a site with sixfold symmetry (b). The restrictions to the possible orientations of the columns are shown in (c). Because of packing considerations, for any particular orientation of a column, as shown on the left, an adjacent column (right) can take up only two of the three possible orientations (i) and (ii). A representation of the orientationally disordered state of the M phase is given in Fig. 9. Note that the molecular columns are shown here in a highly stylized way. They are not necessarily such simple one-molecule-wide stacks.

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