On the structure of the smectic H phase

On the basis of theoretical considerations and experimental evidence it is proposed that in the smectic H phase of TBBA all molecular planes are essentially parallel to the direction of tilt. It is shown that this model does not fit the data on the smectic H phase of BBEA, and so for this phase the previously suggested herringbone packing is retained. A theoretical model is developed for the forces governing the packing in these smectic H phases. This model combines the dipole model of McMillan with interactions between neighboring phenylene groups. The model predicts a parallel arrangement for TBBA and a herringbone arrangement for BBEA, in agreement with the conclusions reached in the first part of the paper.