V. V. Zuev

Stationary statistical size distribution of nematic droplets in the course of the isotropic liquid-nematic phase transition

The statistical size distribution of nematic droplets in the course of the phase transition isotropic liquid-nematic has been analysed using polarizing optical microscopy and described by the model of reversible aggregation. The materials under investigation are low molecular mass nematics, polymeric nematics and polymer dispersed liquid crystals observed at their clearing temperatures in the stationary time regime.

Kinetics of the Ordered Phase Growth in Alkylene‐Aromatic Dimers Across the Phase Transition From Isotropic to Nematic State

Kinetics of the nematic droplet growth during the phase transition from the isotropic to ordered state under cooling at a rate of 1°C/min was studied for two alkylene‐aromatic dimers with different dipole architectures. The linear size (diameter) of droplets revealed in the optical images was treated statistically and the resulting statistical size distributions were described in the framework of irreversible thermodynamics. For the dimer with orthogonal orientation of the dipole moment, two stationary regimes of the nematic phase growth were recognized: nucleus growth and nucleus coarsening. Both regimes were subsequently described using the universal growth law. For the dimer with parallel orientation of the dipole moment, the droplet size remains roughly constant, although the number of nematic germs increases with time.

Kinetics of the growth of the ordered phase at isotropic liquid-nematic phase transition in mesomorphic dimers

The kinetics of the growth of ordered phase drops at isotropic liquid-nematic phase transition in melts of mesomorphic dimers on cooling was studied by polarization optical microscopy. The drop size on microscopic images was analyzed statistically, and the histograms obtained were described by an equation deduced within the framework of equilibrium irreversible thermodynamics. Analysis of the equation parameters revealed three steps of the kinetics of drop growth and allowed their analytical description by a universal scaling function. The correlation between the kinetics of phase transitions and the molecular structure and dipole architecture of the mesomorphic dimers was demonstrated.

Nature of the liquid-crystalline phase in supramolecular linear polymers

The development of the liquid crystal (LC) state in the melt of a supramolecular linear LC polymer based on a diacid and bipyridine base has been studied by IR spectroscopy and polarizing optical microscopy. Relying on experiments on the hydrogen-bonded complex formation and statistical analysis of the formation kinetics of the nematic phase, it is inferred that the system under study behaves like a binary mixture of weakly interacting components rather than a polydisperse polymer.

Fullerene C60 as a stabilizer in the synthesis of liquid-crystalline polyesters

It has been shown that owing to the use of fullerene C60 (∼0.01 wt % based on the monomer weight) as a stabilizer in the synthesis of a liquid-crystalline (LC) polyesters via high-temperature acceptorless poly-condensation, the temperature interval of reaction may be widened to 220°C and the crosslinking side reactions may be eliminated.

Mesomorphic compounds with a rigid T-shaped mesogenic fragment

Mesomorphic polyesters with a rigid T-shaped mesogenic fragment were prepared and studied by polarization optical microscopy, differential scanning calorimetry, and IR and 1H NMR spectroscopy. An increase in the length of aliphatic substituents in the mesogenic fragment leads to a change from the nematic type of the mesophase to the smectic type.

Kinetics of formation of polymer dispersed liquid crystals in a liquid-crystalline polymer matrix

With the use of optical polarization microscopy, the kinetics of phase separation during cooling of molten mixtures of a nematic low-molecular-mass liquid crystal and a liquid crystalline polymer is studied to produce polymer dispersed liquid crystals. The statistical drop-size distribution of a low-molecular-mass liquid crystal is described in the terms of equilibrium thermodynamics of irreversible processes. For a nematic polymer component of a mixture, the analysis of time dependences of the average diameter of drops of a low-molecular-mass liquid crystal makes it possible to reveal two stages in the kinetics of their growth and to describe this process according to the universal law of cluster growth. For a smectic polymer component, the Avrami equation is used to quantitatively describe the kinetics of growth of low-molecular-mass liquid-crystal drops.

The kinetics of cholesteric phase growth from an isotropic melt of liquid crystalline polymer with mesogenic groups in the main chain

The kinetics of growth of cholesteric phase drops in the phase transition (during cooling) of an isotropic melt of a liquid crystalline polymer containing mesogenic groups in the main chain was studied by polarization optical microscopy. The statistical drop size distribution was described in terms of the equilibrium thermodynamics of irreversible processes. An analysis of the time dependences of the mean diameter of drops revealed the existence of two stationary stages of the kinetics of cholesteric phase growth and allowed these stages to be quantitatively described by the universal law of the growth of clusters.

Heterogeneous equilibria and the kinetics of isotropic liquid-nematic phase transition in a multicomponent mixture 4-alkyl-4′-cyanobiphenyls

The isotropic liquid-nematic phase transition and the kinetics of growth of nematic phase drops during this phase transition were studied by polarization optical microscopy and IR spectroscopy for a four-component system during cooling. The statistical drop size distribution was described in terms of the equilibrium thermodynamics of irreversible processes. An analysis of the time dependences of the mean diameter of drops showed the presence of two kinetic stages of nematic phase growth and allowed them to be described by the universal law of cluster growth. In conformity with the Gibbs phase rule, nematic phases with different compositions can coexist at equilibrium.

Callimatic and T-shaped liquid crystalline compounds with fluorinated terminal groups

A series of liquid crystalline polyesters with a rigid T-shaped or a stick-like mesogenic fragment and fluorinated terminal groups of various structures was synthesized and studied by means of polarization optical microscopy, differential scanning calorimetry, and IR and 1H NMR spectroscopy. It was shown that the effect of the fluorinated group on the thermostability of the mesophase depends on the shape of the mesogenic fragment. The thermostability of the mesophase in callimatic liquid crystalline compounds with perfluorinated terminal groups is higher and in those with difluoromethyl terminal groups containing one hydrogen atom is lower compared with their alkyl analogs. This is connected with the possibility of weak hydrogen bonding that destroys the liquid crystalline order. The thermostability of the mesophase in compounds with a T-shaped mesogenic fragment and any fluorinated terminal groups is always higher compared with their alkyl analogs.