Indium tin oxide (ITO) layers are widely used to make electrodes in measuring cells, because these layers are transparent and electrooptical investigations can be performed using such prepared cells. It was found during the dielectric spectroscopy measurements, performed for smectic liquid crystalline mixture, that it is not possible to detect some important relaxation modes in paraelectric SmA*, ferroelectric SmC*, and antiferroelectric SmCA* phases for the frequencies higher than 300 kHz. The measuring cell does not allow to measure relaxations, because its own dielectric behaviour covers the dielectric response of a liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to the finite resistance of ITO layers. The theoretical model was introduced, which shows how to calculate relaxations related to liquid crystals from dielectric response of the empty and filled measuring cell. The proof of strong influence of cell properties on effective (measuring) values of dielectric permittivities was shown.

In search of the long-pitch orthoconic antiferroelectric liquid crystalline mixture 1–3 D’have, K , Rudquist, P and Lagerwall, ST . 2000. Solution of the dark state problem in antiferroelectric liquid crystal displays. Appl. Phys. Lett., 76: 3528–3530. Dąbrowski, R , Gąsowska, J and Otón, JM . 2004. High tilted antiferroelectric liquid crystalline materials. Displays, 25: 9–19. Piecek, W , Perkowski, P and Raszewski, Z . 2010. Long pitch orthoconic antiferroelectric mixture for display applications. Mol. Cryst. Liq. Cryst., 525 (in press) with a broad antiferroelectric smectic phase was successfully formulated. The effect of additive of structurally non-compatible antiferroelectric dopant 4 Hamplova, V , Bubnov, A and Kaspar, M . 2003. New ferroelectric and antiferroelectric liquid crystalline materials containing differing numbers of lactate units. Liq. Cryst., 30: 627–631. [Taylor & Francis Online], [Web of Science ®] [Google Scholar] on the phase structure, transition temperatures, and electrooptical properties of an antiferroelectric orthoconic mixture W1000 3 Piecek, W , Perkowski, P and Raszewski, Z . 2010. Long pitch orthoconic antiferroelectric mixture for display applications. Mol. Cryst. Liq. Cryst., 525 (in press) [Google Scholar] was investigated with thermal, electro-optical, and XRD methods. Experimental data demonstrates that eutectic mixture W1000F obtained by doping of mixture W1000 with highly tilted antiferroelectric dopant maintains the orthoconic properties. The effects of the significant reduction of the rotational viscosity of the admixture is presented and discussed. Comprehensive analysis of parent mixture W1000 and doped mixture W1000F revealed that the affects the intralayer as well as interlayer intermolecular interactions.

Dielectric spectroscopy is a very useful experimental method for liquid crystal investigation. Electrodes made from indium tin oxide (ITO) or gold are widely used in measuring cells. During the dielectric spectroscopy measurements performed for smectic liquid crystalline mixture it was found that detection of some important relaxation modes in paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmCA* phases for frequencies higher than 0.2–0.5 MHz is not possible. The measuring setup does not allow us to measure such relaxations due to its own dielectric response covering the dielectric response of liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to non-zero resistivity of electrode material or non-zero inductivity of connecting wires. In this paper, the new model was introduced. Its final equations show how to calculate parameters of relaxations observed in liquid crystals, from dielectric response of the empty and filled measuring cell. The experimental proof of strong influence of measuring setup properties on effective (measured) values of dielectric permittivities was shown.

MHPB(H)PBC and MHPB(F)PBC were studied by means of refractometric measurements. The refractive indices: n “ (T), n Á (T) and n I (T) were measured using combined methods, applying both appropriately prepared Abbe refractometer and interference wedge. Values of the n “ (T), n Á (T) for the Sm A*, Sm C* and Sm C A * phases are related to the optical axis perpendicular to the proper smectic planes. The results of the optic measurements were discussed.

We report a threshold voltage decrease in a nematic liquid crystal compound, 4-cyano-4′-pentylbiphenyl (5CB), doped with graphene oxide (GO) flakes at a concentration of 0.05–0.3 wt %. The threshold voltage decrease was observed at the same concentration in electro-optic and dielectric spectroscopy measurements. The effect is related to the disrupted planar alignment due to the strong π–π stacking between the 5CB’s benzene rings and the graphene oxide’s structure. Additionally, we present the GO concentration dependence on the isotropic–nematic phase transition temperature, electric anisotropy, splay elastic constant, switch-on time, and switch-off time. The shape and dimensions of the GO flakes were studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The influence of the GO concentration on the physical properties and switching process in the presence of the electric field was discussed.

Dielectric (impedance) spectroscopy of liquid crystals is a powerful experimental technique. It is especially essential because liquid crystals in many applications are still controlled by the electric field. In this paper, the problems with the high frequency (>1 MHz) measurements in classical (in the shape of the flat capacitor) measuring cells are discussed. The procedure for overcoming measurement difficulties was presented and applied to the dielectric response of antiferroelectric, binary mixture. Additionally, the paper presents the first example of extending the measuring range of dielectric spectroscopy from 1 MHz to ~50 MHz by overcoming the parasitic effect related to resonance in measuring setup. Graphical abstract