On the phase transitions of 8CB/Sn2P2S6 liquid crystal nanocolloids

Abstract

Using differential scanning calorimetry measurements, the influence of Sn2P2S6 ferroelectric nanoparticles on the phase transition temperatures of the 8CB liquid crystal is studied. The spontaneous polarization, ionic and anchoring effects are discussed. For low concentration of dopant, the global effect leads to a decrease and an increase of the nematic-isotropic and the smectic A-nematic phase transition temperatures, respectively. For high concentrations, due to aggregates formation, the predominant anchoring effect induces a decrease of the both phase transition temperatures.

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

“…The nanoparticles were prepared by milling microsized particles together with oleic acid in a vibration mill for 120 h. The oleic acid was used as a surfactant on the nanoparticles' surfaces in order to avoid the formation of aggregates. 8 The nanoparticle suspension was obtained at a concentration of 0.1 wt%. The morphology of the resulting particles was characterized using atomic force microscopy (AFM, Veeco multimode equipped with a nanoscope IIIa controller, power of diode laser: 1 mW, l ¼ 690 nm) by depositing the nanoparticle/heptane stabilized suspension on quartz substrate by a dip coating method, as shown in Fig.…”

“…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.…”

“…This hybrid system is obtained by the dispersion of low nanoparticle concentrations (<1 wt%), which allows the modication of several intrinsic properties of the liquid crystal, such as the optical diffraction and birefringence, [1][2][3] the dielectric anisotropy, [4][5][6] and the phase transition temperatures. 7,8 These hybrid materials open new perspectives to improve the performance of liquid crystal based devices. 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.…”

“…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.…”

“…The absence of permanent polarizations of nanoparticles is considered to be responsible for the low reproducibility of the performances of these hybrid systems. 8,15 Recently, the harvesting technique proposed by G. Cook et al has been used for extracting single nanoparticles with strong permanent dipole moments. [16][17][18][19][20][21][22] As reported by A. Rudzki et al, harvested ferroelectric barium titanate (BaTiO 3 ) nanoparticles present a polarization four times higher than that of the non-harvested nanoparticles.…”