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Abstract
Elements of a theory of electrooptically switchable columnar liquid crystals are developed. Assuming spontaneously polarized columns of circular cross section, we consider their dipolar interaction, a special van der Waals interaction of the aromatic molecular cores, and a mean-field theory of a ferroelectric phase transition. Available X-ray data are tentatively assigned to column lattices of low dipolar energy. The agreement between theory and experiments seems satisfactory, especially when the columnar dipole moments per unit length are split and placed at a distance from the column center. However, a dependence of molecular side-chain packing energies on dipolar orientations, so far unmanageable, may intervene and determine which of the low-energy states is the ground state.
Acknowledgments
This work is dedicated to the late Prof. S. Chandrasekhar. He had invited me to give a talk at a conference celebrating the 25th anniversary of his discovery of discotic liquid crystals. It was an honor to attend, but finishing the manuscript he requested took much longer than anticipated and I missed by far the deadline of the conference proceedings [Citation27].
Special thanks go to my former graduate students, Harald Bock and Gabriela Bagordo, who did many of the experiments that are so difficult to understand. Harald Bock got much support from G. Heppke and advice from G. Scherowsky, as well as from their groups. In turn, he inspired them to extend our studies to other materials so that many of the data that I try to explain were obtained by them. I owe additional thanks to G. Heppke for supplying me over the past years with information related to the subject whenever I turned to him.
Notes
Note: The dipoles are central, simply split, or doubly split (see main text for details). The total values are given in the case of unsplit dipole moments, but only the corrections due to splitting are shown in the two cases of splitting. When the dipoles are split, the numbers for the fully ferroelectric state depend on whether the unsplit dipoles are in line or side by side.