Vjacheslav V. Zuev

Electro-optical properties of 4,4-bis-[omega-(4-cyanobiphenyl-4yloxy)alkyloxy]biphenyls nematics

Electro-optical properties of nematics of the trimer series 4,4-bis-[omega-(4-cyanobiphenyl-4yloxy)alkyloxy]biphenyls have been investigated by the method of orientational elastic deformations in electric fields. The number n of CH2 groups in the oxyalkyl fragment was varied from n 2 to n 10. A strong odd-even effect was observed in the optical anisotropy Deltan and in the values of the threshold potential V0 for the trimer nematics. These effects are, respectively, caused by oscillations of the degree of inter- and intra-molecular orientational order when n is varied. The great difference in the dependences of Deltan and V0 on n is discussed and compared with data for dimers.

Polymer-Dispersed Liquid Crystals: Progress in Preparation, Investigation, and Application

Polymer-dispersed liquid crystals (PDLCs), composed of micro-sized liquid crystal domains embedded in a continuous polymer matrix, are an important class of materials that hold promise for many opto-electronic applications. In this review, based on an analysis of research publications appearing between 2006 and 2012, preparation of conventional PDLCs and nanoparticles-doped PDLCs, their properties, and their application for opto-electronic devices are described.

Thermal degradation of para-substituted polystyrenes

Abstract The thermal degradation of a series of para-substituted polystyrenes with electron-donating (CH3, NH2) and electron-attracting (NO2,Cl,Br) substituents has been studied in isothermal conditions at 600°C using pyrolysis chromatography/mass spectrometry and in dynamic conditions using thermogravimetry. The pyrolysis of these substituted polystyrenes gives monomer as the main product for all polymers (60–80 wt.%). The other distribution of products supports the view that thermodestruction of these polymers starts from a random chain scission. The main process for all substituted polystyrenes is depolymerization, similar to unsubstituted polystyrene. In the case of para-substituted polystyrenes a good linear dependence was found between Tmax on the thermogravimetry curve and the Hammett constants of the substituents (Tmax =403.5–67.486 σx). The results indicate that the Hammett relationship can describe quantitatively the trends in Tmax and thus thermostability of substituted polystyrenes and that thermostability of these polymers depends only on electronic nature of substituent and their possibility to stabilise macroradicals forming on chain scission.

Self‐assembling in a living supramolecular linear nematic polymer‐like system

Self‐assembling in a linear supramolecular liquid crystalline (LC) polymer based on 4,4′‐bipyridine and bis‐(4‐carboxyphenyloxycarbonyl)‐heptanoate was studied by IR spectroscopy and optical microscopy. Although just a simple single hydrogen bond is required for the formation of a polymer chain, the reversibility of the hydrogen bonding forces the supramolecular macromolecule to behave under specific conditions similar to a mixture composed of two partly immiscible low molecular weight materials rather than as a polymer. An analytical description indicates that nematic droplets form two overlapping thermodynamically optimised statistical ensembles all across the phase transition in the linear supramolecular LC polymer studied. The kinetics of the nematic nucleus growth in the melted polymer was also studied. The number of generated nematic droplets oscillates with time. Two regimes of the growth kinetics were recognised: (i) nucleation and nucleus growth and (ii) nucleus coarsening, i.e. Ostwald ripening.

Synthesis and characterization of polyurethane-urea microcapsules containing galangal essential oil: statistical analysis of encapsulation

Galangal essential oil (GEO) is known to possess antimicrobial activity (e.g. against Staphylococcus aureus). A way to increase oil lifetime in plants is encapsulation in polyurethane–urea (PUU) microcapsules. In this study, PUU microcapsules with GEO were synthesized by interfacial polymerization at oil–water interface in oil–water emulsion. A statistical analysis of the microcapsule size was successfully applied for characterization of the encapsulation process. Using the model of reversible aggregation, it was shown that the process of encapsulation takes place in the conditions of thermodynamic control. The polymerization conditions (agitation rate in the range 2000–10 000 rpm/min) are the key factors that affect the mean microcapsule size of primary capsules formed during encapsulation. Two complementary processes were determined the mean capsule size during a transformation of these primary microcapsules: break-up and coalescence of oil droplets in the oil-in-water emulsion. The agitation rate does not influence the coalescence of the oil droplets, but the threshold value of agitation speed (in this system 4000 rpm/min) does exist and that is what strongly increases break-up of oil droplets. The higher agitation rate resulted in smaller size of microcapsules (mean diameter decreasing from 5.6 to 4.9 µm for primary capsules and from 13.8 to 9.8 µm for secondary capsules) and with a narrower size distribution. The last mode of encapsulation allows the more effective use the shell material for encapsulating of larger amount of oil.

Kinetics of the isotropic–nematic phase transition in melted multi-component liquid crystal mixtures upon cooling

The kinetics of the phase separation and the nematic phase growth in two melted commercial multi-component liquid crystal mixtures upon cooling was studied using polarising optical microscopy and IR spectrometry. The droplets of the nematic phase revealed in the optical images across the phase transition were segmented and treated statistically. In the resulting size histograms of mixture B, two overlapping statistical ensembles related to two co-existing nematic phases were recognised; these phases were shown to be different in their chemical structures. In mixture A, any separation within the nematic phase was not found. The statistical ensembles of the nematic droplets were successfully described using the principles of irreversible thermodynamics. Analysis of the mean droplet diameter as a function of time allowed recognition of two regimes of the nematic phase evolution: (1) nucleation and rapid nucleus growth and (2) nucleus coalescence. Both the regimes were quantitatively described with the universal law for the cluster growth.

Catalytic Hydrosilylation of Substituted Acetophenones by 1,1,3,3-Tetrametyldisiloxane with Complexes Rhodium (I) and Platinum (II)

The hydrosilylation of a range of para-substituted acetophenones XC6H4COCH3 (X = H, Me, MeO, F, Cl, NO2) with 1,1,3,3-tetramethyl disiloxane mediated by complexes of rhodium (I) and platinum (II) was investigated. The complexes of platinum (II) are less effective than complexes of rhodium (I), but display greater selectivity. Six 1-(1′-arylethoxy)-1,1,3,3-tetramethyl disiloxanes have been synthesized by hydrosilylation using several coupling catalysts.

Orientational Order and Elastic Deformations in Nematic Texturfs of bis-4-Cyanobiphenyloxyalkanes in an Electric Field

Abstract Using the method of orientational elastic deformations in an electric field we investigated the electrooptical properties of nematics of the bis-4-cyanobiphenyloxyalkanes series differing in the number n of CH2 groups in the oxymethylene chain of the molecule. The value of optical anisotropy of nematics (Δ n=ne - no) and threshold electric potentials Vo of deformations of their monodomain planar texture were determined at different temperatures. In both dependences of Δ n and I/Vo on n strong odd-even effect is manifested. However, the characters of alternations observed in them differ greatly. These differences are due to the fact that the value and sign of I/Vo depend not only on the intermolecular (nematic) orientational order but is determind to a much greater extent by intramolecular order which depends on the polar and polarizing architecture of the molecule.

A Facile and Efficient Synthesis of Organocyclosiloxanes

A new facile preparative method for the synthesis of organocyclosiloxanes is reported. Ring closure of the dichlorosilanes with NaHCO 3 and pyridine gave mixture of organocyclosiloxanes with cyclotrisiloxane as a main product.

Investigation of thermal degradation of poly-(4-n-alkylstyrenes) with long alkyl chain (C6–C10) by pyrolysis-gas chromatography/mass spectrometry

The thermal degradation of a series of poly(4-n-alkylstyrenes), from hexyl to decyl, has been studied in isothermal conditions at 600°C using pyrolysis-gas chromatography/mass spectrometry. The type and composition of the pyrolysis products gave useful indications about the mechanism of thermal degradation. It was shown that the main thermal degradation process is depolymerization, like polystyrene. Other thermal reactions involve fragmentation of alkyl side chains. In particular, a new initiation process for depolymerization of polystyrene based polymers was found: a thermal electrocyclic reaction with the formation of divinylbenzene and alkane, and main chain scission with formation of two macroradicals. The formation of cyclic or polyaromatic structures does not take place.