Fluoro-substitution in hydrogen bonding liquid crystal benzoic acid: dielectric, electro-optic and optical proprieties and inducing polar nematic phase

Dielectric and electro-optic properties of cybotactic nematic phase in hydrogen-bonded liquid crystals

“…The thermodynamic melting temperature was that measured upon heating. Table 1 summarizes the domains of existence of the different phases from the present study of 10OBAF and 12OBAF, together with data of 8OBAF from previous work [30]. Both techniques of DSC and POM revealed an increase of melting temperature and a decrease of the nematicisotropic transition with respect to the length of the alkyl chain.…”

“…More surprisingly, recent work on fluorinated HBLC by our group have also revealed the appearance of a low frequency relaxation (about 7 kHz) in the nematic phase [13]. This mode has been ascribed to presence of the ferroelectric clusters and electro-optic measurements clearly indicated the formation of a cybotactic nematic phase [30].…”

“…The natures of these phases were assigned following reference [33]. The dielectric anisotropy, dispersion, relaxation phenomena and loss tangent characteristics of the dielectric behavior of liquid crystals have been determined by fitting the Cole-Davidson distribution of relaxation times (Eq 1) to the real ε' and imaginary ε" parts of the complex dielectric permittivity [30,33]:…”

“…Birefringence was measured through the phase retardation of the sample (δ) using the prism method [30], in which the sample was placed between two crossed linear polarizers with a rubbing direction at 45° to their extinction directions under polychromatic light beam of average wavelength 546 nm. Birefringence (Δn) was measured at several temperatures.…”

“…Such large variety of molecular structures able to form, in particular asymmetric molecules show up specific behavior that may reveal the presence of unexpected and anomalous properties [5,6,13,29,30]. As example, a cybotactic nematic phase due to the presence of ferroelectric clusters has been observed [29].…”