Polar order in columnar phase made of polycatenar bent-core molecules

Columnar phases made of polycatenar molecules with bent-shaped mesogenic cores are studied. The polar order in this system is associated with the change of the column building blocks from flat disks (Col(h) phase) into cones (Col(h)P(A) phase), which allows for axial polarization of the columns. The nature of the Col(h) and Col(h)P(A) phase transition changes from first order for short homologues to continuous for the longest one. This can be attributed to decreasing intercolumnar interactions due to broadening of the columnar scaffold made of partially melted terminal alkyl chains. Decrease of intercolumnar interactions is also responsible for a strong increase of the pretransitional fluctuations in the Col(h) phase. The mesophase observed for the longest homologues is reminiscent of the relaxor phase observed for solid crystals.