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A possibility was assessed to modify physico-chemical properties of ferronematic mixtures by introducing additional mesogenic and non-mesogenic components. The mixture, consisting of RM734 and DIO at the 70:30 weight ratio of the components, was doped with nematic 5CB and its chiral isomer CB15. This allowed a substantial lowering of the ferronematic temperature range, as well as induction of helical twisting in both nematic (N) and ferronematic (NF) phases. The effects of 5CB and CB15 on the NF to N phase transition were nearly identical, but the isotropic transition temperature decreased more strongly upon addition of CB15. Optical transmission vs. temperature measurements showed lower transmittance in the NF phase, probably due to scattering on the domain boundaries. In the vicinity of the NF → N transition, a noticeable range of anomalously low transmission was noted both on heating and cooling, suggesting a complex character of molecular reorientation features. In the chiral NF (N*F) system, helical twisting was recorded using Grandjean-Cano wedge, with the helical pitch decreasing upon cooling in both N* and N*F phases. In the cooling mode, transient undulations emerged in the N*F phase. The complex picture of the ferronematic transition is supported by POM images taken at different temperatures. [ABSTRACT FROM AUTHOR]

Morphologic and thermo-optical properties of liquid crystalline material exhibiting multiple phase transitions were investigated in this work. Investigations were carried out for both the direct (by heating) and the reverse (by cooling) phase transitions. Thermo-morphologic properties of the heterophase regions of phase transitions were investigated. Temperature dependences of the optical transmission were studied, the mean optical density of crystalline state, smectic C, smectic A and nematic mesophases was estimated, temperature widths of the heterophase regions of crystal ↔ smectic C, smectic C ↔ smectic A, smectic A ↔ nematic and nematic ↔ isotropic liquid phase transitions were determined with high accuracy. [ABSTRACT FROM AUTHOR]

Bias field, spectral, and temperature-dependent optical studies on conventional and de Vries type ferroelectric liquid crystals (FLCs) are presented. The mixing of ethanol into de Vries FLCs strongly influences their Sm C* and Sm A* phases, due to the influence on molecular randomization. Such comparative optical studies may be used as an effective tool for the preliminary detection of molecular randomization in addition to other conventional techniques. [ABSTRACT FROM AUTHOR]

Abstract: The optical transmission of small aluminum oxide particles in liquid crystal 4-methoxybenzylidene-4′-butylaniline (MBBA) and dual-frequency liquid crystal mixture consisting of 4-n-pentyl-4′-cyanobiphenyl (5CB), 4-hexyloxyphenyl ester 4′-hexyloxy-3-nitrobenzoic acid (C2), 4-n-pentanoyloxy-benzoic acid-4′-hexyloxyphenyl ester (H 22) was studied. It was established that there was a transmission band which was shifted on application of a voltage and depended on temperature. At using the dual-frequency liquid crystal as a matrix, a transmission band maximum switched at changing of the frequency. The experimental results are explained by the optical homogeneity of the system in a narrow wavenumber interval when the refractive indices of the particle material and the matrix are close, and also by re-orientation of the liquid crystal molecules when a voltage is applied. The obtained results can be used in constructing of tunable filters and compact monochromators. [Copyright &y& Elsevier]

A gold film with subwavelength nanoholes on a glass substrate was fabricated through electron beam lithography and its extraordinary optical transmission (EOT) was characterized. By applying a liquid crystal overlayer to the gold film, its EOT can be further enhanced by ~11% due to the refractive index matching of the dielectric media on its two sides. By controlling the alignment of the liquid crystal molecules, a highly reversible and reproducible tuning of the transmission peak in both intensity and position is demonstrated. [ABSTRACT FROM AUTHOR]

We obtained a new system containing nematic liquid crystal doped with nanostructured copolymer-clay particles. The clay (Cloisite-type) was modified by copolymerization of maleic anhydride and divinyl benzene and the nanocomposite has intercalated structure. Current-voltage characteristics of the liquid crystal/copolymer-clay systems were analyzed and the electro-optical response at heating -cooling cycles for different applied electric fields is discussed. Dielectric spectroscopy measurements in the low frequency domain have shown different regimes of its temperature dependence as function of the sample nature and the applied voltage. Comparison is made with the bulk liquid crystal. Changes of the phase transition temperature are thus revealed. [ABSTRACT FROM AUTHOR]

We have developed a dual-frequency liquid crystal consisting of 4-n-pentyl-4′-cyanobiphenyl (5CB), 4-hexyloxyphenyl-4′-hexyloxy-3-nitrobenzoate (C2), and 4-butyl-4′-(hexyloxyphenyloxycarbonyl)phenyl carbonate (H22). We have measured the frequency dependences of the longitudinal and transverse components of the dielectric constant of the mixture and we have determined the frequency regions of positive and negative dielectric anisotropy. We show that for certain changes in the frequency of the applied electric field while the magnitude of the field remains the same, the transmission region of the AlO particles - dual-frequency liquid crystal system switches from one wavelength to the other. The experimental results are explained by the optical homogeneity of the system in a narrow wavelength interval when the refractive indices of the particle material and the matrix are close, and also by reorientation of the liquid crystal molecules as the frequency of the applied voltage changes. [ABSTRACT FROM AUTHOR]

Abstract: Characterization and investigation of the physical properties of two new analogs of salicylaldimine compounds, which were synthesised for the first time by our group, are reported in this work. 5-(10-undecenyloxy)-2-[[[4-hexylphenyl]imino]methyl]phenol and 5-(10-undecenyloxy)-2-[[[4-hexyloxyphenyl]imino]methyl]phenol have been studied. Different degree of mesomorphism has been found in these analogs. Typical textures and temperatures of the direct and reverse phase transitions, taking place in these analogs, are presented. Temperature dependences of the optical transmission for both heating and cooling are given. [Copyright &y& Elsevier]

Abstract: We report here uniform and defect-free homeotropic alignment of nematic liquid crystal having negative dielectric anisotropy (Δε<0) on cleaned substrates, which can be changed to bright state (homogeneous alignment) by applying an electric field. However, non-uniformity in the bright state would not be desirable for display devices. Therefore, silane treated and gently rubbed substrates have been utilised to obtain uniform bright state. Several textural, dielectric, and optical transmission studies have been carried out to explore the applicability of studied material in the liquid crystal display applications. Furthermore, such materials could also be useful for making colourful displays without colour filters. [Copyright &y& Elsevier]

We study ester-type liquid crystal, 4'-cyanophenyl 4-n-hexyl benzoate and its homologue 4'-cyanophenyl 4-n-pentyl benzoate. We used the Thermally Stimulated Depolarization Currents method and found information about phase transition temperature, and activation energies. The temperatures of phase transitions were compared to those obtained by classical DSC/DTA measurements. Simultaneously with the TSDC, we measured the optical transmission; we found a decrease of the optical transmission when it was measured after a greater pre-applied polarizing electric field. [ABSTRACT FROM AUTHOR]

Dispersions were studied of multiwall carbon nanotubes in cholesteric liquid crystals of three types: nematics with chiral dopant, mixtures of cholesterol derivatives, and similar mixtures close to smectic-A transition. In the first two cases, no appreciable effects of nanotubes upon selective reflection spectra were noted, while optical transmission increased significantly at the isotropic phase transition. Aromatic and steroid matrices differed significantly in this respect, though in both cases the nanotubes were apparently oriented along the directors of quasi-nematic layers. In the third case, nanotubes slightly but clearly affected the measured selective reflection peaks, suggesting suppression of the smectic-A phase formation. [ABSTRACT FROM AUTHOR]

We have studied the optical transmission of a small aluminum oxide particles – liquid crystal (4-methoxybenzylidene-4′-butylaniline) system. We have observed that at room temperature, in the spectrum we observe a transmission band with maximum at 1896 cm–1, which is shifted toward shorter wavelengths on application of a voltage and depends on temperature. The experimental results are explained by the optical homogeneity of the system in a narrow frequency interval when the refractive indices of the particle material and the matrix are close, and also by reorientation of the liquid crystal molecules when a voltage is applied. [ABSTRACT FROM AUTHOR]

Abstract: Optical transmittance and electric conductivity were studied for dispersions of multiwall carbon nanotubes (MWCNTs) in nematic liquid crystals of four different chemical classes (cyanobiphenyls, Schiff bases, azoxy compounds, and cyclohexanecarboxylic acids). The optical transmittance data showed deep integration of MWCNTs into the orientationally ordered nematic structure. The effect observed was apparently related to interactions between the MWCNTs and mesogen matrix, which appeared to be weaker when the nematic host was formed by non-aromatic molecules. Dependences of the electrical conductivity versus applied DC voltage were noticeably different for different nematic matrices. Voltage amplification of electrical conductivity was observed at relatively higher voltages (above 10V). The increased threshold voltages for electrohydrodynamical instability in nematics were observed in MWCNT-doped dispersions. [Copyright &y& Elsevier]

We have synthesized new functionalized copolymers of the type divinyl benzene - maleic anhydride (DVB-MA) in order to ensure a better compatibility with the penthyl-phenol group of the liquid crystal. These particles have been mixed by stirring and ultrasound with nematic liquid crystals ZLI 1221 (Merck), concentration 5% b.w. (copolymer/LC). We applied cycles of temperature and electric field, corresponding to the TSDC method. We measured the depolarization currents and simultaneously the optical transmission as a function of the electric field and temperature. We obtained information regarding the conduction mechanism, the distribution of the activation energy and the influence of the polarizing voltage on the optical transmission. [ABSTRACT FROM AUTHOR]

For nematic liquid crystals (LC) with small (0.01-0.15 wt%) concentration of multiwall nanotubes (NT) dispersed therein, optical transmission and electric conductivity were measured as a function of temperature. Characteristic changes in transmission at the nematic-isotropic phase transition temperature have been noted, suggesting that NT dispersed in the LC matrix behave in a manner similar to that of the conventional non-mesogenic dopants. This picture is supported by the electrical conductivity data. The electrical conductivity increased noticeably within ∼0.01-0.1 wt% range of NT concentrations in the LC matrix, and a marked difference in the measured electrical conductivity values for the LC matrices of different polarity (e.g., cyanobiphenyl and azoxy) was observed. [ABSTRACT FROM AUTHOR]

We have synthesized polymer particles of the type alternated copolymers DVB- maleic anhydride. The dimensions of the obtained particles have been determined by electron microscopy and are in the range 1-2 μm. These particles have been mixed by stirring and ultrasound with nematic liquid crystals ZLI 1221 (Merck), in a concentration of 5% b.w.(polymer/LC). We applied cycles of temperature and electric field, corresponding to the TSDC method. We measured the depolarization currents and simultaneously the optical transmission as a function of the electric field and temperature. We obtained information regarding the conduction mechanism, the activation energy and the pre-exponential frequency factor in the Arrhenius diagrams. The dipolar current obtained is consequent to a superposition of a dipolar distribution with a wide spectrum of relaxation times. [ABSTRACT FROM AUTHOR]

Abstract: Peculiarities of the biphasic regions at the direct and reverse phase transitions between homeotropic oriented nematic mesophase and isotropic liquid have been investigated in detail in this work. The shift of phase transition temperatures to the low temperatures by the reverse phase transitions have been observed for this mesophase. Nonlinearity of thermotropic and thermo-optical properties at the phase transitions between nematic mesophase and isotropic liquid have been found. [Copyright &y& Elsevier]

Liquid crystal microdisplays are heavily used in applications ranging from static and quasi-static images to video-rate displays. Antiferroelectric liquid crystals with asymmetric response exhibit good properties to be employed in this kind of devices, for example in mobile telephones. Asymmetric response arises from dissimilar surface conditioning onto the cell glass plates. The resulting asymmetric antiferroelectric devices feature multiplexed analogue grey scales with very simple driving schemes. In this work, a comparative study of properties of antiferroelectric liquid crystal cells with symmetric and asymmetric response is carried out. Asymmetric cells give rise dissimilar current peaks depending on the polarity of the applied waveform. This effect may stem from various contributions, such as ionic conductance and free charges accumulated superimposed to the symmetric antiferroelectric response. [ABSTRACT FROM AUTHOR]

In this paper we examined the electrical and optical properties of the pure liquid crystal 8CB and in a composite system obtained by surface modified particles ZrO2and the liquid crystal 8CB. Using the Thermally Stimulated Depolarisation Current(TSDC)method we obtained information regarding the conduction mechanism, the activation energy and the pre-exponential frequency factor in the Arrhenius diagrams. We study the dependence of phase transition temperatures on the magnitude of the polarizing d.c. electric field previously applied on the sample. The optical transmission is slightly dependent on the polarization field and the thermal switch behavior was obtained at the nematic–isotropic transition. The TSDC and optical results are compared with the ones obtained by rheology. [ABSTRACT FROM AUTHOR]

In this paper we examined the electrical and optical properties of a new composite device containing layers of a nematic liquid crystal and cellulose derivative. Using the thermally stimulated depolarization current (TSDC) method we obtained information regarding the conduction mechanism, the activation energy, and the pre-exponential frequency factor in the Arrhenius diagrams. The optical transmission is slightly dependent on the polarization field, and the thermal switch behavior was obtained at the nematic-isotrop transition. When a.c. voltage is applied to the sample, the optical transmission depends strongly on the field amplitude, and a very good contrast is obtained. [ABSTRACT FROM AUTHOR]

In this work, the electro-optic response of V-shape chiral smectic liquid crystal materials with low frequency triangular waveforms has been analysed. An experimental set up allowing simultaneous acquisition of optical and electric response has been prepared. Besides, the transmission of the display has been modelled with a cell equivalent circuit. In this sense, a circuit simulator has been used to derive the value of the different circuit elements. The electro-optic behaviour of the cells has been evaluated for several frequencies and voltage amplitudes; theoretical results have been compared to experimental measurements. The optical response predicted by the model fairly matches the actual device. [ABSTRACT FROM AUTHOR]