A. V. Sharapova

Liquid-crystalline polypropyleneimine dendrimer as a stationary phase for gas chromatography

The adsorption properties of a stationary phase for gas chromatography based on a Chromaton N-AW diatomite support modified with a 2K2S16 mesomorphic polypropyleneimine dendrimer are studied. Using the Rohrschneider constants, the studied stationary phase is classified as low polar. It is shown that the new stationary phase is suitable for the separation of both isomers and mixtures of organic substances bearing various functional groups up to a temperature of 150°C.

Thermodynamics of solution in liquid crystalline poly(propyleneimine) dendrimers by inverse gas chromatography

Thermodynamic characteristics of infinitely diluted solutions of n-alkanes and n-alcohols in the columnar and isotropic phases of poly(propyleneimine) dendrimers, generations 1-3 (G1-G3), have been investigated by inverse gas chromatography (IGC). Effects of the dendrimer structure, the chemical nature and molecular size of the non-mesogenes on the ability to get dissolved in the liquid crystalline phases are discussed. The compatibility of the low-molecular compounds with the anisotropic phases is stated to increase with generation G.

Mesomorphism of thermotropic poly(propyleneimine) dendrimers and phase equilibria in systems on their basis

The thermotropic mesomorphism of poly(propyleneimine) dendrimers of first, second, and third generations has been studied by the methods of polarization thermomicroscopy and DSC. Phase diagrams for the binary systems of dendrimers with n-amyloxy-n′-cyanobiphenyl calamite liquid crystal and hexa(pentyloxy)triphenylene discotic liquid crystal have been constructed. Measurements have been carried out over the entire concentration range at temperatures corresponding to the stable states of nematic, columnar, and isotropic phases. The effects of the chemical nature and shape of linear and cyclic mesogen molecules on the manifestation of mesomorphism in LC dendrimers are considered.

Thermodynamic parameters for the dissolution of n-alkanes and n-alkanols in a liquid-crystalline polypropylenimine dendrimer: A gas-chromatographic study

Thermodynamic parameters for the dissolution of n-alkanes (C7-C11) and n-alcohols (C5-C9) under infinite dilution in the columnar and isotropic phases of a polypropylenimine dendrimer have been determined by inverse gas chromatography. Thermodynamic functions have been investigated as a function of the phase state of a mesogen, the length of alkyl chains of sorbates, and temperature. For the dissolution of low-molecular-mass organic compounds, a higher endothermic effect corresponds to a larger entropy factor with its positive deviation from ideality. The dominant effect of the entropy constituent of the Gibbs energy on the dissolution of sorbates in a high-molecular-mass LC solvent has been revealed. The Rohrschneider constants have been estimated for the stationary phase based on the dendrimer. The experimental data indicate the low polarity of the sorbent that is close to those of phenyl-containing siloxane phases.

Chromatographic properties of fullerene modified with liquid crystal p,p'-azoxyphenetol

Stationary phases for gas chromatography based on liquid crystal p,p′-azoxyphenetol applied onto Chromaton N-AW bearing a layer of C60 fullerene were studied. The thermodynamic properties of the adsorption of n-alkanes and n-alcohols on the mesogen surface were studied at low occupancies. Test mixtures of structural isomers of substituted benzene and polycyclic aromatic hydrocarbons were analyzed in a wide temperature range from 100 to 240°C.

A Thermodynamic Approach to the Selectivity of Liquid Crystalline Reentrant Phases

The thermodynamic characteristics and selectivity of sorption of disubstituted benzene, pyridine, and naphthalene by the p-n-nonyloxybenzoyloxy-p′-cyanoazobenzene, p-n-hexyloxycinnamoyloxy-p′-cyanoazobenzene liquid crystalline phases and their mixture was studied by gas chromatography. The reentrant nematic phase of a mixture of mesogens was found to possess high selectivity to structural isomers. The results of manifestation of liquid crystalline phase selectivity are discussed on the basis of the enthalpy and entropy characteristics of solution of sorbates.

Activity coefficients of butanol isomers in liquid crystalline cholesteryl tridecylate according to data of reverse phase gas chromatography and tensiometry

The reverse phase gas chromatography technique was used to determine the activity coefficients of butanol isomers at infinite dilution in the smectic, cholesteric and isotropic phases of cholesteryl tridecylate. Experimental parameters with which the chromatographic process may be viewed as balanced and proceeding within the bulk of the liquid crystal were defined. Alcohol activity coefficients in binary systems with cholesteryl tridecylate determined by the gas chromatographic and tensiometric techniques were found to be in good agreement. A conclusion is reached on the suitability of the reversed-phase gas chromatographic technique for studying smectic and cholesteric liquid crystalline phases.

Phase equilibria in liquid crystalline systems based on polypropylenimine dendrimer

The thermodynamic characteristics of infinitely dilute solutions of saturated hydrocarbons in the columnar and isotropic polypropylenimine dendrimer phases were studied by gas chromatography. The contribution of the entropy Gibbs energy component to the solution of sorbates in a liquid crystalline solvent at a positive deviation from ideality was found to be predominant. A phase diagram of the binary system consisting of the dendrimer and nematic p-amyloxy-p′-cyanobiphenyl was constructed. The effect of the chemical nature and shape of component molecules on the mesomorphism of the mixtures is discussed.

The influence of the generation number of liquid-crystalline polypropyleneimine dendrimers on the sorption of low-molecular-weight compounds

The thermodynamic characteristics of ultimately dilute solutions of n-alkanes and n-alkanols in columnar and isotropic poly(propyleneimine) dendrimer phases of three generations (G1-G3) were studied by reversed-phase gas chromatography. The influence of the structure of dendrimers and the chemical nature and the size of nonmesogen molecules on their ability to be dissolved in liquid crystalline phases is discussed. It was found that the compatibility of low-molecular-weight compounds with anisotropic phases increased as the number of dendrimer generation grew.