Roman Dabrowski

Influence of rigid core structure on layer tilt and mesomorphic properties in homologous series of three ring antiferroelectric esters

Mesomorphic properties (phase transitions enthalpies and temperatures) and the dependence of smectic layer spacings upon reduced temperature for eight homologous series of three ring ester such as: (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl or (S)-(+)-4-(1-methylheptyloxycarbonyl)-3-fluorophenyl or (S)-(+)-4-(1-methyl-heptyloxycarbonyl)-2-fluorophenyl 4-(perfluoroalkanoyloxyhexyloxy)biphenylates and 4-(alkanoyloxyhexyloxy)-biphenylates, and (S)-(+)-4-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-(perfluoroalkanoyloxyhexyloxy)benzoates and 4-(alkanoyloxyhexyloxy)benzoates were described. The terminal chain fluorinated compounds have SmC*anti-SmC*-SmA-Iso phase sequence and a high tilted (orthoconic) antiferroelectric phase in broad temperature range.

Homologous series of fluorinated antiferroelectric liquid crystals: a comparative study of physical properties and the electro-optical performance

Recently the investigation in the field of LCD technology has been boosted by the availability of new materials. The new group of fluorinated mesogens has been recently synthesized in Poland. In this work we have been focused on investigations of properties of materials having the broad temperature range of antiferroelectric phase. Such key factors as apparent tilt angle and structural properties and electro-optical performance have been studied by means of electro-optical and X-ray methods. The bend molecular shape and the presence of fluorinated tail has been assumed as a factor leading to an extremely high apparent optical tilt. The length of the fluorinated chain seems to affect th mesogenic behavior.

Synthesis and mesomorphic properties of isothiocyanatotolanes

The synthesis, mesomorphic properties and visible spectra of 4-substituted alkyl-, alkoxy-, alkylcyclohexyl and alkylcyclohexylethy1-4-isothiocyanatotolanes have been described. Multicomponent mixtures with birefringence higher than 0.4 and low viscosity have been formulated.

Improved Miesowicz Viscometer

Abstract The main features of the Miesowicz torsionai viscometer with automatized detection of the plate movement are described. An application of the viscometer to study the anisotropy of viscosity in nematic mixtures RALLE5 and WARSAW4 is shown as an example.

Broad temperature range antiferroelectric regular mixtures

Tristate regular mixtures with different electro-optical properties such as threshold voltage, saturation voltage, holding ratio and response time are presented. The relation of properties with the structure of compounds is discussed. All of mixtures show only moderate dynamic and static contrast but big gray level scale without hysteresis for positive and negative field driving.

2H NMR and X-Ray Studies of a Substance Exhibiting Crystal-Like Smectic Phases

DSC, polarizing optical microscopy and X-ray diffractometry were used to investigate the mesomorphic behaviour of 4-n-butyl-4′-acetyl-biphenyl, which resulted to exhibit a smectic E and, possibly, a smectic K phase. Additionally, 2H NMR spectroscopy was applied on a selectively deuterated sample to study the properties of alignment of the mesophases within a magnetic field, as well as to characterize molecular dynamics. Two motional processes were found to be active in the smectic E phase, namely fast π-flips of the benzene rings and molecular self-diffusion about the herringbone bidimensional lattice of the layers. No molecular overall diffusional motions were observed by either 2H NMR spectroscopy or dielectric relaxation measurements.

Electrochemical activity of some different iron polyphthalocyanines for the oxygen reduction reaction in acidic medium

Abstract The electrochemical activity of iron polyphthalocyanines (pPcFe) synthesized from pyromellitic dianhydride (PMDA) or tetracyanobenzene (TCB) and dicyan It was found that pPcFe derived from PMDA has the highest activity and that the temperature dependences of electrical conductivity in vacuum and oxygen

Electro-optical properties of mixtures with the induced antiferroelectric phase

In some mixtures composed of ferroelectric components the induced antiferroelectric phase was observed. Two mixtures of this kind, both exhibiting antiferroelectric order in a broad concentration range, were investigated. The effect of electric field of various strengths on optical properties of these mixtures was studied. In small electric fields the modulation of light intensity occurred, which amplitude in ferroelectric phase was much higher than in the antiferroelectric one. In mixtures with induced antiferroelectric phase we detected a large hysteresis of the transition temperature between ferroelectric and antiferroelectric sates. In high electric fields thresholdless switching was observed in the hysteresis range. The presence of the thermal hysteresis of the CA* - C* phase transition can be considered as a mark of the V-shaped switching. In bulk samples the C*- phase is stable in, this temperature region, where the V- shaped switching was observed in thin samples.

12.1: High Birefringence LCs for Color-Sequential LCDs

High birefringence (0.3<Δn <0.4) and relatively low viscosity liquid crystal mixtures containing isothiocyanato tolane and isothiocyanato terphenyl liquid crystals are developed. The response time of 1.52 ms using a 1.6-μm TN cell is demonstrated.

Determination of same changes in rotational potentials between ferro-and antiferroelectric phases

Rotational potential of molecule in smectic phases, introduced by Zeks, includes two important parts: dipolar as well as quadrupolar ones. The first part is valid for chiral molecules only, whereas the second one is important for chiral and achiral molecules. The question arises: Whether shape of rotational potential changes when the phase transition between SmC* and SmCA* appears? In our opinion, close to the temperature of phase transition (FLC-AFLC) magnitudes of both, dipolar and quadrupolar parts change. Quadrupolar coupling is more important for antiferroelectric phase, while dipolar factor overwhelms quadrupolar one, for ferroelectric phase.