Influence of dispersed aerosil particles on the collective dynamic modes in a ferroelectric liquid crystal with polarization sign reversal

Broadband dielectric spectroscopy was applied to study the influence of the dispersed hydrophilic aerosil particle densities on the second-order smectic-A–smectic-C* phase transition and polarization sign reversal in the ferroelectric liquid crystal S-(−)-2-methylbutyl 4-n-nonanoyloxybiphenyl-4′-carboxylate. With increasing aerosil concentration the dielectric strength of the soft and the Goldstone mode considerably decreases and the complete disappearance of the Goldstone mode at ρs = 0.20 g/cm3 occurs along with significant broadening of the soft mode. The characteristic frequency of the Goldstone mode slightly increases with increasing density of the silica particles. The frequency degeneracy taking place in the smectic-A–smectic-C* phase transition is removed in the presence of aerosil and an increase in the frequency gap is observed. In a point of polarization sign reversal a rapid drop of the dielectric strength and the disappearance of the Goldstone mode was detected for bulk and confined ferroelectric liquid crystal. However, with increasing concentration of aerosil particles the dielectric strength of the Goldstone mode decreases as a function of temperature stronger below than above the sign reversal point. The characteristic frequency of the Goldstone mode below the point of polarization sign reversal decreases with increasing aerosil concentration.