Electric field effects on phase transitions in the 8CB liquid crystal doped with ferroelectric nanoparticles

Abstract

The influence of a low ac electric field on phase transitions is discussed in the case of a nematic liquid crystal 4-n-octyl-4^{'}-cyanobiphenyl (8CB) doped with Sn_{2}P_{2}S_{6} ferroelectric nanoparticles. The phase-transition temperatures obtained from temperature-dependent dielectric measurements were higher than those determined by the calorimetric method. This difference is explained by the presence of the measuring electric field which induces two effects. The first one is the amplification of the interactions between the nanoparticle polarization and the liquid-crystal order parameter. The second one is the field-induced disaggregation or aggregation process at high nanoparticle concentrations.

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

“…This is often achieved by coating the surface with monomolecular organic materials, surfactants (stabiliser), or ligands. For instance, oleic acid, 7,10,17,20,21,[24][25][26][27] selenium docosane 28 and dodecylbenzenesulphonic acid 29,30 have been widely utilized for the coating of NPs.…”

Reconfigurable Periodic Liquid Crystal Defect Array via Modulation of Electric Field

“…For f >100 kHz, a dielectric relaxation process begins, thus the phase shift between the field and the polarization occur. Then the dielectric heating causes increase in the temperature of the sample, in turn, decreasing the effective birefringence of the LC medium . The light retardation τ = 2 πd Δ n eff /λ is proportional to the effective birefringence Δ n eff and thickness d at a wavelength (λ).…”

A comparative study of nematic liquid crystals doped with harvested and non-harvested ferroelectric nanoparticles: phase transitions and dielectric properties

“…For the non-harvested nanoparticles dispersed with the 8CB liquid crystal, we previously showed that the volume concentration, f NP ¼ 0.08%, allows optimization of the effects of the nanoparticles. 8,13 Moreover this concentration corresponds to a homogeneous dispersion. For these reasons, this concentration was chosen for nanocolloid #2.…”

“…The cells were then introduced in an appropriate heating stage and measurements were made using a Hewlett Packard 4284A Impedance Analyzer covering the frequency range from f ¼ 20 Hz to f ¼ 1 MHz. 13 The amplitude of the measuring sinusoidal electric eld was xed at 0.1 V. For each mixture, a minimum of two samples were measured for each orientation. Fig.…”

“…5,[9][10][11] Due to the effects of spontaneous polarization, doping with ferroelectric nanoparticles leads to an increase in the liquid crystal order parameter. 7,8,12,13 The permanent polarization of nanoparticles depends on their size, shape and aggregation, the mechanical treatment, etc. 14 In some cases, elaboration leads to nanoparticles with different spontaneous polarizations; a part of them can present a weak or null spontaneous polarization.…”