The electric permittivities, refractive indices and densities of the homologous series of alkyl-cyano-biphenyls (CnH2n+1.φ.φ.CN) have been measured as a function of temperature in the nematic phases for n = 5 to 9, and in the smectic phases for n = 8 and 9. The results have been analysed in terms of the Maier and Meier theory to yield values for the molecular dipole moments and polarizabilities. Kerr effect measurements on dilute solutions of 44′-n-pentyl-cyano-biphenyl at different temperatures are reported, and in conjunction with similar dielectric and optical measurements have provided results for the free molecule dipole moment and polarizabilites; values for the higher homologues are predicted using a bond additivity model. Bordewijk's theory is applied to the permittivity measurements, and using appropriate molecular parameters, dipole-dipole correlation factors are calculated.

The Dielectric and Optical Properties of the Homologous Series of Cyano-Alkyl-Biphenyl Liquid Crystals

Gold nanoparticles offer the possibility of creating metamaterials; however, such nanoparticles are not particularly stable. Conversely, liquid crystals offer the possibility of creating self-organizing and self-assembling materials, which can be designed to be relatively stable. Potentially, combining these two concepts could provide materials that can be induced to assemble in a controlled way and that would have unique optical properties. This article describes some of the groundwork made in the preparation of stable liquid-crystalline metamaterials and the investigation of their structures and physical properties. In particular, spherically substituted materials are found to be deformed into tactoids with anisotropic properties, most notably their dielectric anisotropies.

Self‐Assembly and Shape Morphology of Liquid Crystalline Gold Metamaterials

The viscosity coefficients η1, η2, η3 and η12 of 4-n-pentyl-4'-cyanobiphenyl, 4-n-octyl-4'-cyanobiphenyl, 4-methoxy-4'-n-butylazoxybenzene and an aromatic ester mixture were determined in the nematic phase region. Except for 4-n-octyl-4'-cyanobiphenyl, the viscosity coefficients of the liquid crystals show the following properties: 1) Three of the viscosity coefficients are related by an equation of the form Σ Aiηi = 0, in which the corresponding constants Ai are very similar for the different liquid crystals. 2) The equation ηi =aijηj + bij is valid with the exception of the neighbourhood of the clearing point. 3) The reduced viscosity coefficients 3ηi/(η1 + η2 + η3) of the different liquid crystals exhibit a very similar dependence on the reduced temperature and a nearly linear dependence on the degree of order. The viscosity coefficients η2 and η12 of 4-n-octyl-4' -cyanobiphenyl show a divergence at the transition to the smectic phase, whereas η1 and η3 show the normal temperature dependence.

A Comparative Study of the Viscosity Coefficients of Some Nematic Liquid Crystalss

4'-n-Pentyl-4-cyanobiphenyl (5CB) is a room temperature nematic liquid crystal with a high positive dielectric anisotropy and a high chemical stability. Many experimental results concerning the elastic and dielectric constants of 5CB are available in the literature, although there is often no satisfactory agreement between the experimental data obtained by different groups, especially as far as the dielectric constants are concerned. Furthermore, no detailed investigation of the temperature dependence of the elastic and dielectric constants close to the nematic-isotropic transition temperature T NI has yet been reported. In this paper, we report the measurement of the elastic and dielectric constants of 5CB, and the temperature behaviour close to T NI has been investigated in detail. The experiment consists in the measurement of the director deformation induced by an electric field using simultaneously both a dielectric and an optical method. The simultaneous use of these two methods provides an indirect ...

Elastic, dielectric and optical constants of 4'-pentyl-4-cyanobiphenyl

Broadband dielectric spectroscopy (up to 109 Hz) is employed to study the molecular dynamics of the liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) in the free bulk phase and confined in cylindrical channels of Anopore membranes having a diameter of 0.2 μm and length of about 60 μm. The bulk samples of 5CB orient almost homeotropically between the untreated metal electrodes of the measurement set-up, and two relaxation processes are observed: the slower δ-relaxation is assigned to hindered rotation (180° flips) of the molecules around their molecular short axis, and a faster second process is attributed to the tumbling of the molecules about this axis. In the confined 5CB samples, the membrane pores align the nematic director axially or radially depending upon their surface preparation. Planar (axial) alignment is always found in untreated membranes, whereas radial alignment was achieved by treatment with decanoic acid. Consequently the director field is fixed perpendicular or parallel to the el...

Dielectric properties of the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl in porous membranes

The electric permittivity of nematic 44′ n-pentylcyanobiphenyl has been measured in the presence of electric and magnetic fields. Values of the permittivity components for the aligned state have been obtained and analysed in terms of the statistical theory of Maier and Meier. The behaviour of bulk samples of the material in electric and magnetic fields has been investigated, and yielded a mean permittivity for the non-aligned state. The macroscopic behaviour is discussed in terms of the continuum theory. Variable frequency measurements have shown the presence of a dispersion region in e∥ at about 5 MHz.

P. G. Cummins

Papers

The Dielectric Properties of Nematic 44′ n-pentylcyanobiphenyI