Leszek R. Jaroszewicz

Dielectric modes in antiferroelectric liquid crystal observed at low temperatures

A broad temperature antiferroelectric binary mixture has been investigated by means of dielectric spectroscopy. The sample was cooled down to –70°C. It was found that the sample was still in antiferroelectric phase. This is the widest antiferroelectric mixture ever seen (∼170°) in which three well-separated modes have been detected at room temperature. In addition, the bias field influence on existing modes has been observed. All modes change their strengths with bias field. Results show that the fastest mode, called X mode previously, gradually disappears around –30°C. When the temperature decreases below –40°C, one can indisputably observe additional mode, faster than X mode. This mode (named as Y mode) observed for extra low temperatures is bias independent. It can be the molecular mode, connected with rotation around long molecular axis. The rotation around short molecular axis seems to be blocked in antiferroelectric packing. To calculate parameters of observed modes, Cole–Cole model was used. The parameters of Y mode are discussed in this article.

Influence of the bias field on dielectric properties of the SmCA* in the vicinity of the SmC*–SmCA* phase transition

In a large class of smectic mixtures prepared at our University, the phase transition between chiral ferroelectric smectic C (SmC*) and chiral antiferroelectric smectic C (SmCA*) phases can be observed on cooling. Under bias field the temperature of the phase transition SmC*−SmCA* decreases (ca. 100°C in the investigated mixture). The transition is called: unwound SmC*−twisted SmCA* phase transition. The Goldstone mode in SmC* phase is reduced by a direct current field while two modes (PH and PL) in the SmCA* phase are amplified. The amplitude of the fast X mode observed in the SmCA* phase is reduced. The aim of this paper is to show how parameters of the modes in SmCA* phase (calculated from Cole–Cole model) change with bias voltage—when twisted structure in SmCA* phase is gradually unwound. The character of the modes observed in SmCA* is discussed. A new effect is shown: a high value of dielectric loss is detected in the unwound SmC* phase, which is very close to SmCA*.

Liquid crystal cell for space-borne laser rangefinder to space mission applications

Liquid crystal cell (LCC) for space-borne laser rangefinder to space mission applications was developed, manufactured and tested under cooperation between Military University of Technology (MUT) in Poland and Vavilov State Optical Institute (Vavilov SOI) in Russia. LCC operates in twisted nematic mode, commutating the polarization plane of a laser beam working at 1.064 μm and the energy density not smaller than 0,15 J/cm2 at the pulse duration about 8 ns. The transmission of LCC is not smaller than 95% at the aperture diameter not less than 15 mm. Switching on and switching off times in a 2.5-μm thick LCC driven by voltage of 10 V are not larger than 0.7 ms and 7 ms, respectively, in the operating temperature range from 20°C to 40°C. The LCCs developed in MUT were positively tested under space requirements in Vavilov SOI.

The influence of structure and concentration of cyano-terminated and terphenyl dopants on helical pitch and helical twist sense in orthoconic antiferroelectric mixtures

A bicomponent mixture in the orthoconic aniferroelectric phase, based on three-ring esters with fluorine atoms and ether group in a nonchiral chain, was doped with a variety of cyano-terminated compounds containing different numbers of phenyl rings in a rigid core and a terminal chain of different chirality. Compounds with two chiral chains were added to the basic mixture. The influence of the structure and concentration of dopant on the temperature-dependence of helical parameters, such as helical pitch and twist sense, were assessed by spectrophotometric and polarimetric methods. Long cyano-terminated compounds were found to be better than the other dopants tested for improving the usable properties of the antiferroelectric mixtures.

Fiberscope-based engine condition monitoring system

The article presents the engine condition monitoring system. The system uses dependence between amount of rub products gathered in lubricating oil and current wear condition of device. The measure method bases on ferrographic method. Images are taken from sample and magnified by fiberscope, and then converted by CCD camera into digital form. Then raster images are classified by dedicated computer system. This paper presents actual state of system research.

Spectral Properties of Nematic Liquid Crystal Mixtures Composed with Long and Short Molecules in THz Frequency Range

Properties of liquid crystal materials in THz frequency range can be interesting from application point of view. In this paper the influence of short and long molecules added to liquid crystal 6CHBT were investigated. Change of refractive indices and absorption coefficients for 6CHBT mixtures were compared in the 0.3 - 3 THz frequency range. Influence of temperature on the mentioned parameters of liquid crystal were investigated. Our study show that even a slight change in shape and the composition of the molecules dopants affects the macroscopic properties of liquid crystal. These properties depend on the length of chains, the number of benzene or cyclohexane rings or the spatial distribution of molecules and the interactions between them in the liquid crystal mixture. Spectra measurements on the terahertz time-domain spectrometer were performed.

Numerical analysis of THz metamaterial with high birefringence liquid crystal

We analysed the response of a tunable liquid crystal metamaterial (MTM) transducer in the terahertz frequency range. The MTM structure is based on the rod double-split square resonators (SSR) with back-to-back orientation. A full-wave analysis technique based on the finite-difference time-domain method (FDTD) was performed using QuickWave 3D electromagnetic solver. Terahertz transmission properties of the MTM structure can be controlled by the director of the liquid crystal layer. The main aim of this work is to determine the impact of the size of the SSR of the MTM transducer on scattering parameters of the analysed MTM transducer at terahertz frequency range. Numerical simulations were performed in the range 0.32–0.44 THz.

Measurement of elastic constants of nematic liquid crystals with use of hybrid in-plane-switched cell

A new method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is experimentally verified. The main concept relies on exploiting only the electric field and determining magnitudes of nematic elastic constants from threshold fields for Freedericksz transitions in only one hybrid in-plane-switched cell. In such cell the deformations of an investigated liquid crystal are controlled by three separated pairs of electrodes confining measurement domains. In two of them inter-digital electrodes are mounted on one cell cover. Splay, twist and bend elastic constants can be measured by a proper choice of electrodes’ configuration together with orienting cover coatings (without applying magnetic fields). In this paper, we describe layout of our cells and results of experimental tests by using different liquid crystals: 5CB and 6CHBT (with positive dielectric anisotropy), Demus’ esters (with negative dielectric anisotropy) and new liquid crystals mixtures produced in our university.

Optical properties of a liquid crystal with small ordinary and extraordinary refractive indices and small optical anisotropy

Optical properties of a nematic liquid crystal with small refractive index and small birefringence were studied. The ordinary and extraordinary refractive indices and birefringence were measured as functions of temperature by using an Abbe refractometer and wedge nematic cells. From values of these indices the nematic orientational order parameter was calculated by using several methods and corresponding mathematical models. Kuczyński et al. method was found to be suitable for determining the order parameter also for materials featuring small ordinary refractive index, with unknown density.

On the influence of the chiral side linking bridge type upon the synclinic vs. anticlinic balance in the case of 2′,3′-difluoroterphenyl derivatives

A homologous series of new ferro- and antiferroelectric liquid crystals, containing 2′,3′-difluorosubstituted terphenyl core as a mesogenic core, has been recently synthesised. Synthetic routes and mesomorphic properties were described. Liquid crystal phases were preliminarily determined by thermomicroscopic and microcalorimetric measurements and verified by dielectric measurements and miscibility methods. Temperatures and enthalpies of phase transitions are given.