logo logo logo

Department of Dielectrics

Institute of Physics of the Czech Academy of Sciences


fig

Liquid crystals

Home Research Highlights Projects Equipment Publications People
fzu fig

Organic nanotubes created from mesogenic lactic acid derivatives

We found a facile route how to prepare nanotubes from rod-like mesogens dissolved in typical organic solvents. For selected types of chiral rod-like molecules, both enantiomers as well as the racemic mixtures, the nanotubes are formed by slow evaporation from a solution, regardless the solvent, concentration or deposition type. Obtained supramolecular assemblies were studied using various experimental techniques and nanotubes of 50-60 nm diameter described. We proposed rolling-up mechanism related to the surface tension difference at the opposite layer surfaces.

(show more)
fzu fig

Unusual behaviour under the applied electric field for new cholesteric liquid crystals with extremely short pitch

Unusual behaviour of new cholesteric liquid crystals has been observed under applied electric field. Positive dielectric anisotropy causes reorientation of the long molecular axis along the applied electric field direction. Due to extremely short pitch length a stripe texture has been observed under applied electric field. A model based on disclinations has been proposed and anchoring energy evaluated.

(show more)
fzu fig

New type of dimers composed of bent-core molecules connected through their central cores

Structurally new type of dimers composed of bent-core molecules connected through their central cores has been prepared and studied. The switching behaviour in the applied electric field is reported.

(show more)
fzu fig

All-organic liquid crystalline radicals with a spin unit in the outer position of a bent-core system

All-organic paramagnetic liquid crystals offer the advantage of a long-range order of liquid crystalline phases and the magnetic properties of the individual molecules. In such systems, the magnetic properties can be modified by phase transition or the application of external fields. In our work paramagnetic all-organic bent-core liquid crystals having the radical-bearing unit (TEMPO) in the terminal position of an elongating side arm are studied.

(show more)
fzu fig

Unique effect of the electric field on a new liquid crystalline lactic acid derivative

We found a unique effect of the applied electric field for new chiral liquid crystalline compound, namely lactic acid derivative. We observed reversible transformation of the planar TGBA texture to the homeotropic one, homogeneously dark in crossed polarizers. The transformation is an analogy of the Frederiks transition known in nematics and only rarely can be found for smectics.

(show more)
fzu fig

Molecular tilt induced by gold nanoparticles or clusters of nanoparticles in the liquid crystalline smectic A phase of “de Vries” type of compound

For the first time a tilt of molecules around the gold nanoparticles or their clusters has been observed in the liquid crystalline smectic A phase. We have shown the tilt is a consequence of interaction of the molecules with the surface of nanoparticle leading to a local smectic A-smectic C transition. Nanoparticles attracted to edge dislocations enable to visualize them under an optical polarizing microscope.

(show more)
fzu fig

Nanocomposite of superparamagnetic maghemite nanoparticles and ferroelectric liquid crystal

We present a novel type of hybrid nanocomposite prepared by mixing maghemite nanoparticles (MNPs) and a chiral liquid crystalline compound. The multiferroic system exhibits the ferroelectricity as well as superparamagnetic (SPM) properties. The impact of nanoparticles and effect of applied magnetic field on ferroelectric liquid crystalline properties were established. The magnetic behavior is typical for a system of SPM nanoparticles with inter-particle dipolar interactions and surface spin disorder.

(show more)
fzu fig

Reentrancy phenomenon of a smectic A phase in chiral liquid crystalline compounds

Unique sequence of phases was discovered in a chiral smectic, namely reentrance of orthogonal paraelectric A phase below the ferroelectric C phase. This behavior was explained by non-monotonous temperature dependence of the principal coefficient in the free energy expansion and microscopically by changes of molecular conformations and intermolecular distances due to occurrence a lateral bulky group in the molecule. This phenomenon is accompanied with anomalies in dielectric, optical and switching properties.

(show more)