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Three new homologous bent-shaped mesogens with terminal octyloxy P8, decyloxy P10 and dodecyloxy P12 groups were synthesized. Calorimetric, X-ray and electro-optic investigations prove the existence of two mesophases of the SmCPA type for compound P10 but only one SmCPA phase for the homologues P8 and P12. The static dielectric permittivities of compound P12 and that of the low-temperature phase of substance P10 are in the order of 30 and agree with results on bent-core mesogens published before. Surprisingly, the dielectric permittivities of P8 and of the high-temperature phase of P10 are of about 1000. We explain this extremely high dielectric response with the soft reaction of ferroelectric units in the external electrical field. [ABSTRACT FROM AUTHOR]

The physical behaviour, especially the dielectric properties, of two series of isomeric compounds formed by banana-shaped molecules is reported. The feature of all liquid crystalline substances investigated is the formation of a ferroelectric short range order. In one layer of the SmCPA phase the spontaneous polarisation shows in one direction and in the following in the opposite resulting in an antiferroelectric behaviour. It is demonstrated that the molecular origin of the polarization is connected with the perpendicular dipole moments. From the two relaxation modes seen the first results from ferroelectric units and the second from the reorientation of the molecules about the long axes. The collective character of both motions is demonstrated. The same mechanisms appear in the columnar phase, but they behave in a different way due to the different structure. Strong changes of the dielectric properties are observed at the transition from the isotropic in the liquid crystalline phase, but astonishingly not between both mesophases. [ABSTRACT FROM AUTHOR]

Dielectric measurements on a binary system of two liquid crystalline diols were carried out. These show a SmA and a cubic phase. In the middle concentration range of the system, a columnar phase is induced. The self assembly of the molecules giving different liquid crystalline phases is clearly seen in the dielectric spectrum, and therefore details of this process may be discussed. All the samples show a high frequency dielectric absorption which is related to the dynamics of the network of hydrogen bonds. In the columnar phase an additional low frequency mechanism is seen which may be caused by the internal dynamics in the columns. [ABSTRACT FROM AUTHOR]

Investigations on the phase diagrams of two bi-component mixtures of liquid crystals are presented. Whereas in one of the bi-component systems, smectic A (SmA) phase is seen to be induced, in the other case the so-called nematic “island” has been observed. The dielectric properties of magnetically oriented sample forming nematic phase and induced smectic phase in one of the mixtures, and a nematic “island” and SmA phase in the other mixture, were measured in the frequency range from 1  Hz to 10  MHz at different temperatures. The transition temperatures obtained from the polarizing microscope and differential scanning calorimeter measurements agree well with the dielectric relaxation data. [ABSTRACT FROM AUTHOR]

A smectic hexatic phase with tilted molecules is assumed to be confined between two plane boundaries. At a finite boundary distance two dielectric modes are excited by an a.c. external electric field. Using the elastic continuum theory, equations for the relaxation times and the corresponding dielectric susceptibilities are derived and discussed in the limit of high boundary distances and for different material parameters. [ABSTRACT FROM AUTHOR]

It was found that doping of tiny ferroelectric particles to a nematic liquid crystal(LC)strongly affects dielectric properties of the system. The doping increases dielectric response of the LC due to interaction between LC molecules and particles, which possess large dipole moment and high polarisability. The suspension reveals high dielectric response on either side of the Curie temperature, TCurie, and peculiarity at the vicinity of TCurie. This result points at retention of dipole ordering above Curie temperature that may be a result of a memory effect. [ABSTRACT FROM AUTHOR]

It was found that doping a nematic liquid crystal (LC) with a small amount of ferroelectric nanoparticles strongly affects the dielectric properties of the system. In particular, adding the ferroelectric particles results in a shift of the absorption bands corresponding to the rotation of liquid crystal molecules around their short axes to lower frequencies and in an increase of the amplitude and with of the absorption bands. This suggests that strong interactions occur between the LC molecules and the particles, caused by the large dipole moment and high polarizability of the ferro-particles. The ferroelectric particles affect not only dielectric losses, but also dielectric permittivity of the system. Specifically, the static dielectric permittivity and the dielectric anisotropy of the suspension are more than twice that of the pure LC. [ABSTRACT FROM AUTHOR]

A new series of five-ring banana-shaped mesogens derived from isophthalaldehyde was synthesized and investigated. Some of the compounds exhibit a B 2 -B 4 dimorphism. The mesophases were characterized alternatively by optical methods, X-ray studies, and dielectric and electro-optical measurements. [ABSTRACT FROM AUTHOR]

Dielectric investigations on a magnetically oriented sample forming N, SmA, SmC and B[sub 2] phases were carried out. The sample shows a negative dielectric anisotropy in the N state and a strong increase of the static dielectric constants perpendicular to the director in the ensuring 'classical' phases. This proves directly the strong and continuous increase of the positive dipole correlation in the lateral direction due to the steric interactions of the bent-shape molecules. From a dynamical point of view, the SmA and SmC phases of this sample show deviations from the classical phases of rod-like molecules. Crystallization did not allow us to extend the dielectric measurements into the B[sub 2] state. [ABSTRACT FROM AUTHOR]

Banana-shaped five-ring mesogens derived from either isophthalic acid or 4-bromoisophthalic acid have been synthesized. It is shown that the melting and clearing points of the bromine-substituted compounds are markedly decreased in comparison with the analogous unsubstituted compounds. On the basis of X-ray diffraction studies and NMR measurements, as well as dielectric and electro-optical investigations, the mesophase of these compounds could be identified as a B[sub 2] phase. [ABSTRACT FROM AUTHOR]

Dielectric measurements on two samples formed from banana-shaped molecules with terminal alkyl or alkyloxy groups were carried out in a frequency range between 10[sup -3] Hz and 10 MHz. Both samples exhibit B[sub 2] and B[sub 3] phases; one of them has a B[sub 4] state as well. As usual, two ranges of relaxation were detected in the B[sub 2] phase, the fast reorientation about the long axes of the molecules and a slow collective process. Only one dielectrically active low frequency process could be separated in the B[sub 3] and B[sub 4] phases; this is probably related to the dynamics of superstructures. The high frequency limit of the dielectric constants gives a hint that neither phase is a classical solid. A quite strong increase in the conductivity at the transition into the B[sub 3] phase is critically discussed. [ABSTRACT FROM AUTHOR]

Dielectric measurements in the frequency range 0.01 Hz to 10 MHz on a liquid crystal material with SmB/N dimorphism confined to randomly oriented and interconnected mesoporous (pore diameter 2-10 nm) and macroporous glasses (pore diameter 86 nm) were carried out. In the macroporous glasses the liquid crystal behaves similarly to the bulk phase, but the phase transition temperature SmB-N is suppressed. In the mesoporous glass the transition SmB-N is completely suppressed. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) images reveal that the liquid crystalline B[sub 2] phase has no helical superstructure, in contrast to the B[sub 7] phase. This is demonstrated on comparing the AFM images of focal-conic domains in the smectic A, cholesteric, B[sub 2] and B[sub 7] phases. The B[sub 2] and B[sub 7] phases are phases formed by banana-shaped molecules. The results point to the existence of ferroelectric clusters with a random size distribution which also cause the low frequency dielectric relaxation. [ABSTRACT FROM AUTHOR]

A new achiral five-ring banana-shaped mesogen is presented which has a cyano substituent in the 4-position of the central core. Microscopical, X-ray, dielectric and electro-optical investigations give evidence for the unusual phase sequence B[sub 2], SmC, SmA. The B[sub 2] phase shows an antiferroelectric switching behaviour; the spontaneous polarization was found to be 330 nCcm[sup -2]. [ABSTRACT FROM AUTHOR]

AFM investigations of a glassy heterogeneous system consisting of an oligomeric cholesteric liquid crystal and the hydrophobic aerosil R812 were carried out. With increasing aerosil concentration, a suppression of the characteristic cholesteric surface pattern was observed. Typical separated aerosil aggregates appear in the samples. Their size and form change from small lumps through bigger rod-like entities to large crystallite-like aggregates of aerosil particles. This matches with observations of light scattering of systems with low molecular mass liquid crystals and of the memory effect. The pitch of the cholesteric fingerprint pattern slightly decreases with increase in the aerosil concentration. [ABSTRACT FROM AUTHOR]

Two samples consisting of banana-shaped molecules with terminal alkyloxy or terminal alkyl groups were investigated. Dielectric measurements prove the existence of two absorption ranges up to 10 MHz. The high frequency process is related to the reorientation of the bulky rigid core characterized by a strong positive dipole correlation in the B[sub 2] phase. The sample with the alkyloxy groups should show a third absorption range at higher frequencies due to the fast reorientation of the end groups. The low frequency process seen only in the B[sub 2] phase is explained by the dynamics of ferroelectric clusters. [ABSTRACT FROM AUTHOR]

Two strongly polar 4-(4-cyanobenzyloxy)benzylidene 4- n -alkylanilines were synthesized for the first time and mixed with the hydrophilic aerosil A 300. The compounds, showing a rich polymorphism, and the mixtures were investigated by calorimetric and dielectric methods. Phase transitions of first and second order were detected. Neither the phase transition temperatures nor dielectric relaxation times are strongly influenced by addition of aerosil up to 20%. [ABSTRACT FROM AUTHOR]

Examines the association of a positive dipole correlation in the isotropic phase at the I/B[sub 2] transition of a liquid crystal. Formation of nematic cluster; Influence of a local ferroelectric order to the dielectric constant during phase transition; Capacitance of the electrical double layer at low frequencies.

Dielectric measurements of oligomeric cyanobiphenyls connected to a pyramid-like central unit are presented. The data are interpreted in terms of the dynamics of the liquid crystalline units. There is no indication of reorientation of the central unit as whole or co-operative effects of piled up central units. [ABSTRACT FROM AUTHOR]