smectic-B Phase Research Articles

Shear Mechanical Properties of Freely Suspended Liquid-Crystal Films in the Smectic-Aand Smectic-BPhases

The shear mechanical properties of freely suspended films of liquid crystal, p-butoxybenzylidene-p'-octylaniline (BBOA or 4O.8), have been measured in the smecitc-A and smectic-B phases. All films showed solidlike response well above the bulk A-B transition temperature. Both the in-plane shear modulus and shear dissipation exhibited a very strong frequency dependence in the A and B phases. Films which were two molecules thick showed anomalous behavior at much higher temperatures than thicker films.

Raman Scattering Study of Fluidlike Molecular Dynamics in A Smectic-B Liquid Crystal

Abstract A Raman scattering study has been made in N-(p-butoxybenzylidene)-p-n-octylaniline. Sharp changes in the intensity ratios near frequency shifts of 1200 and 1600 cm−1 occur at the solid to smectic-B transition, with no further changes upon heating to the isotropic liquid. The results suggest the smectic-B phase already exhibits completely fluidlike dynamics of the central molecular core.

Ultrasonic study of a smectic-Bliquid crystal

Anisotropy in the velocity and attenuation of longitudinal ultrasound was studied for the first time in a stable smectic-B liquid crystal (..beta..-methyl-butyl-methoxybenzylidene amino cinnamate). Anisotropy in the velocity was found to be consistent with the predictions of the Martin-Parodi-Pershan hydrodynamic theory in both smectic-A and -B phases, but was significantly smaller than when measured in the same material by Brillouin scattering. Furthermore, strong dispersion was observed near the smectic-A--smectic-B phase transition for sound propagating perpendicular to the symmetry direction.

Liquid Crystalline Phases in N-(4-n-alkylbenzylidene)-4′-n-alkylanilines

Abstract The mesomorphic behavior of N-(4-n-alkylbenzylidene)-4′-n-alkylanilines is investigated and nematic as well as smectic-B phases are found at comparatively low temperatures. Long aliphatic substituents on the aldehyde side of the molecule favor the smectic-B phase. Observations on smectic-B textures, transition enthalpies and density measurements are reported. The simple method used to determine transition temperatures despite impure samples can also be applied to other compounds, e. g. yielding 21.6 - 47.5 °C for the nematic range of MBBA.

“Melting” of the aliphatic chains in a solid ⇃ smectic-B transition

Abstract EPR measurements of a spin label dissolved in the smectic-B phase of 4, 4′-dioctadecyloxy-azoxybenzene indicate than the solid ⇃ smectic-B transition corresponds to a loss of orientational order of the terminal aliphatic chains. This can be considered as a “melting” of the chains an interpretation which is in agreement with the transition enthalpies.

Nuclear magnetic resonance studies of smectic liquid crystals

Nuclear magnetic resonance measurements in the smectic liquid crystalline phases of seven thermotropic compounds are reported. The compounds investigated are: terephthalbis(butylaniline); ethyl(methoxybenzylidene)amino] cinnamate; diheptyloxyazoxybenzene; octyloxybenzoic acid; dipentylazoxycinnamate; diethylazoxycinnamate; diethylazoxybenzoate. Proton spectra at 100 MHz of the neat liquid crystal molecules, as well as of simple probe molecules dissolved in small amounts in the liquid crystal, were studied in their dependence on temperature and on sample orientation with respect to the magnetic field. The results show that good alignment of the smectic phases can be obtained by cooling from the isotropic or the nematic phase in a magnetic field; once aligned, the smectic planes conserve their original orientation on rotation of the magnetic field. The results are consistent with the following models of the smectic phases: Smectic-A is uniaxial and there is fast rotational and translational molecular diffusion. Smectic-C is similar to smectic-A, except that the molecules are tilted with respect to the smectic layers. A model, in which the direction of tilt is free to reorient, is used to interpret the behavior of the NMR spectra of smectic-C on rotation of the magnetic field. The magnitude of the tilt angle can be estimated from such an interpretation. Two of the compounds studied have a smectic-B phase. In one it is uniaxial, while in the other it is biaxial. The NMR results are consistent with this classification. They also show that molecular diffusion is considerably slower in the smectic-B than in the smectic-A and -C phases: the correlation time is of the order of 10−6 sec. In an appendix the formal theory of molecular orientation in a biaxial liquid crystal is given.