Induced birefringence in the isotropic phase of cholesteric liquid crystals

The birefringence induced by an acoustic field in the isotropic phase of the cholesteryl myristate cholesteric liquid crystal has been measured. The measurements were performed at sound frequencies of 3.2 and 9.8 MHz in a wide temperature range. Based on the results of the measurements of the induced birefringence, the relaxation time of the orientation of the liquid crystal molecules is estimated.     

On a reentrant isotropic phase in disc-like liquid crystals

A binary mixture of two disc-like liquid crystals 2, 3, 7, 8, 12, 13-hexa-n-tetradecanoyloxy and 2, 3, 7, 8, 12, 13-hexa (4-n-dodecyloxybenzoyloxy) truxenes exhibits an isotropic phase above and below the temperature existence range of a columnar mesophase.     

Non-linear dielectric effect in the isotropic phase of antiferroelectric liquid crystals

We have theoretically studied the non-linear dielectric effect in the isotropic phase of antiferroelectric liquid crystals on the basis of phenomenological theory. We find an analytical expression for the non-linear dielectric effect in the isotropic phase of the transition. The temperature dependence of the non-linear dielectric effect is presented in the isotropic phase of the transition.     

Non-linear dielectric effect in the isotropic phase of ferroelectric liquid crystals

We use a phenomenological model to find theoretically the non-linear dielectric effect (NDE) in the isotropic phase above the isotropic to chiral smectic-C (I-SmC^*) phase transition. We find an analytical expression for the NDE in the isotropic phase above the I-SmC^* phase transition. The temperature dependence of the NDE is presented in the isotropic phase of the I-SmC^* phase transition.     

Magnetic and electric birefringence in the isotropic phase of nematic liquid crystals

A theory is developed of the anomalous magnetic and electric birefringence in the isotropic phase of nematic liquid crystals taking into account orientational correlations between neighbouring molecules. Use is made of a modification of Bethe’s method due to Krieger and James, and the properties of the system are derived in terms of a single parameter, viz., the two-particle interaction constant. The expressions for the magnetic and electric birefringence are similar in form to those given by the phenomenological model of de Gennes. Theoretical curves forp-azoxyanisole reproduce the trends in the observed data. A calculation of the nematic-isotropic transition point confirms that this treatment is an improvement over the mean field approximation in describing pre-transition phenomena in the isotropic phase.     

Nonexponential nuclear spin-lattice relaxation in the isotropic phase of thermotropic liquid crystals

In the isotropic phase of nematic and smectic liquid crystals T₁ of CH3 and chain protons is larger than that of ring and ring-neighboured protons being caused by fast CH₃ reorientation and internal motions in chains, respectively.     

Light scattering by some nematic liquid crystals due to phase transitions

New computer modelling of light scattering and its propagation through liquid crystal has been presented using T-matrix method in the structural phase transition regions. Numerical aspects of light scattering process, which are based on numerically solving Maxwell's equations, were calculated for some nematic liquid crystals. Firstly, we described in detail T-matrix method for computing light scattering from nematic liquid crystals and presented results of benchmark computations for the considered model. We reported results of extensive calculations for polydisperse, randomly oriented rod-like multilayered systems (nematic liquid crystals). Our results are associated with light scattering by ferroelectric and ferroelastic materials.     

Blue phase of liquid crystals: Light scattering and elastic moduli

Summary The theory of the optical, electro-optical and elastic properties of liquid-crystal blue phases is presented. The efficiency of the optical methods of study of blue phase is underlined. The effects of the many-wave diffraction optics in blue phases are discussed in detail. The universal temperature dependence of the blue-phase order parameter is found for the experimentally observed blue phases. Work presented the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30–October 2, 1987.     

Self-diffusion of nematic liquid crystals in the isotropic phase near the nematic-isotropic transition

Self-diffusion coefficients of two nematic-liquid crystals, PAA and MBBA, were measured by the spin-echo technique over a temperature-range ≈30°C above the nematic-isotropic transition. For both systems, activation energies derived from such measurements agree fairly well those determined earlier from viscosity data.     

Optical model of transient light scattering in ferroelectric liquid crystals

A static optical model is developed for the effect of field-induced transient scattering on coherent light transmission through ferroelectric liquid crystals. Scattering processes are described by introducing an optically anisotropic medium containing scatterers (transient domains). The results presented in the paper are obtained for a plane parallel layer of ferroelectric liquid crystals with a planar helicoidal structure under normal illumination with a linearly polarized plane wave. An analysis is presented of the coherent transmittance of the layer in static applied electric fields.     

Far-infrared spectroscopy of liquid crystals

The far-infrared spectra of 7CB in the unaligned and aligned nematic phases are markedly different in overall intensity and absorption band-shape detail. Effects persist into the apparently isotropic solution as typified by CH₂Cl₂ solutions.     

Dynamic light scattering as a probe of orientational dynamics in confined liquid crystals

The eigenmodes of director orientational fluctuations in nematic liquid crystals in confined geometries were studied both theoretically and experimentally by dynamic light-scattering tehnique. The fundamental mode of the orientational fluctuations shows a crossover from bulk behavior, dominated by bulk elastic constant K, to surface dominated one, in which the relaxation rate is determined by the ratio of surface anchoring strength W and viscosity eta. The contribution of surface viscosity zeta is also significant when its characteristic length zeta/eta becomes comparable to the size of the confined system. It was measured in nematic liquid crystal in cylindrical pores of polycarbonate (Nuclepore) membranes to be of the order of 10 nm.     

Infrared versus light scattering techniques to monitor the gel to liquid crystal phase transition in lipid membranes

In this study, Fourier transform infrared, Raman and Brillouin spectroscopy have been used to study lipid phase behavior of hydrated as well as dried multilamellar l ‐α‐phosphatidylcholine assemblies, in order to compare limitations and potentials of the different techniques. Dried lipid samples have been studied in the presence and absence of trehalose, which is known to affect the phase behavior of these systems. The methylene C‐H stretching (2800–3000 cm⁻¹) region in infrared (IR) and Raman spectra provided mutually consistent information on the rearrangement of lipid acyl chains occurring at the lipid melting temperature. IR spectra have a higher signal‐to‐noise ratio, thus permitting a more precise evaluation of the melting temperature. In the hydrated lipid samples, the C‐H stretching region in the Raman spectra is less affected by the contribution of water compared with that in the IR spectra. Raman spectra are particularly suitable to simultaneously study both lipid and water contributions allowing to distinguish ice from non‐frozen water below 0 °C. Brillouin light scattering was used to probe the collective dynamics, i.e. the propagation velocity and the attenuation of longitudinal acoustic modes in the lipid samples. Lipid phase transitions are evident from a change in the temperature behavior of the acoustic velocity. Moreover, a strong relaxation process with a characteristic time of 14 ps was observed in the sample dried without trehalose with a maximum in acoustic attenuation at about 45 °C, which likely reflects the rearrangement of acyl chains. Copyright © 2015 John Wiley & Sons, Ltd.     

丙酮酸脱氢酶的光子相关动态光散射研究

本文利用动态光散射技术研究丙酮酸脱氢酶,得到其微观结构方面的若干信息.测量出其PDC结构及E_2-X-K结构的半径;发现在较低浓度下,聚集现象可以忽略,尺寸分布是单分散性分布,动态光散射谱的线宽Γ与散射波矢q分别呈Γ∝q~2及Γ∝q~3关系.而在较高浓度下,Γ∝qα,α为分数,这时尺寸分布里多分散性分布.     

Statistical approach to light scattering by convex ice crystals

Within the geometric optics approximation, the phase functions of randomly oriented ice crystals are calculated as a series relative to multiplicity of internal collisions of light inside the particles. In the case of convex crystals, it is shown that the coefficients of the series provide the most information about the crystal shapes, while the angular functions of this series are weakly dependent on the shapes. The prevailing role of the term corresponding to one internal collision is emphasized. Three numbers describing a distribution of the single-collision scattered light among the aureole and halos of 22 degrees and 46 degrees prove to be the basic parameters by which to characterize scattering by hexagonal ice crystals.