Gapless phason in an antiferroelectric liquid crystal

Abstract

The phason dispersion in the antiferroelectric Sm-c: liquid crystalline phase of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate has been studied by quasielastic light-scattering experiments. The phason is found to be gapless as predicted for a Goldstone mode recovering the broken continuous symmetry. The dispersion has a minimum at q -2qc, where qc is the wave vector of the unperturbed Sm-C:l' structure. These results are consistent with the alternating-tilt model of the antiferroelectric Sm-C:l' phase.

Ferrielectric smectic phases: Liquid crystal structure and macroscopic fluctuations

“…Although the sets of experiments on the new series of liquid crystals embraced X-ray diffraction [ 12,131, differential scanning calorimetry (DSC) [ 5,14,15], helicoidal structure studies [ 1,161, phason dispersion analysis [17] and conoscopic observations under an external electric field [6,7,18,19], the structures of the reported phases are not yet clear. The X-ray studies on oriented plates show the absence of any detectable modulation of electronic density along the z axis, which suggests strongly that the tilt angle is identical from one layer to another.…”

Modifying optical Bragg reflections from an antiferroelectric liquid crystal with photopolymer networks

“…However, additional higher resolution x-ray resonant experiments [7,8], as well as optical rotation and ellipsometric data [9,10], strongly support a deformed clock model. The various phases are now classified according to their unit cell [11]. On this basis, the ferroelectric (Sm-C * ) phase consists of single, tilted, and polar smectic layers.…”

Stability of aperiodic crystals

“…Another effect is the presence of defects which have a more important effect on phasons than on acoustic modes. Systems where underdamped phasons have been found are liquid crystals [13].…”