Molecular and collective relaxations of ferroelectric side chain liquid crystalline polysiloxanes

Abstract

The influences of mesogenic group chemical structures on dielectric relaxation behavior were investigated for ferroelectric side chain liquid crystalline polymers (FLCPs). The relaxation time and activation energies of the Goldstone mode, α-, and β-relaxations decrease with increasing spacer length because of the plasticizer effect of the spacer. Moreover, the relaxation intensity increases with increasing spacer length for FLCPs. An FLCP with a longer spacer length exhibits a higher mesogenic group mobility, and subsequently leads to easier reorientation toward the alternating electrical field. An increase in mesogenic core rigidity results in an increase in the relaxation time and activation energies, and a decrease in the relaxation intensities for the Goldstone mode, α-, and β-relaxations. Moreover, the β-relaxation is suppressed and cannot be observed in the glassy state for FLCPs containing naphthyl biphenylcarboxylate as the mesogenic group. Shorter relaxation time, smaller activation energies, and higher intensity of the α-, and β-relaxations were obtained for FLCPs containing chiral moiety with a flexible heptyl alkyl chain. However, the relaxation intensity of the Goldstone mode for FLCPs containing this chiral moiety was smaller than that for FLCPs containing the chiral moiety with a butyl alkyl chain. For FLCPs containing a chiral moiety with two asymmetrical centers, their Goldstone mode relaxation showed larger amplitude. The α- and β-relaxations are suppressed for these FLCPs because of the dense packing and memory effect of the smectic phase. The relationship between the chemical structure of the mesogenic group and dielectric relaxations is discussed in great detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2035–2049, 2006