DIFFERENT DIELECTRIC BEHAVIORS IN THE S* _Cα PHASE: CONFRONTATION BETWEEN EXPERIMENTAL RESULTS AND THEORETICAL PREDICTIONS

Abstract

Experimental and theoretical results are compared to explain the dielectric properties in the S* _cα phase of two homologous of the nFF series. Using the clock model and calculations developed by N. Vaupotic and al., the temperature evolutions of the Goldstone and soft modes in the S* _cα phase are studied. Two different behaviors are evidenced depending on the azimuthal angle difference α between two adjacent layers: when α is limited, the Goldstone mode is detected in all the S* _cα phase; for higher values of α, the soft mode is predominant near the S_A−S* _cα phase transition and the Goldstone mode is observed only at lower temperature. A good agreement is obtained with previous experimental results in considering the influence of the azimuthal angle α and its temperature evolution. These predictions are confirmed with optical period measurements performed on the same compounds.

Key Words:

• Dielectric relaxation
• clock model
• antiferroelectric liquid crystals
• helical pitch