Vladimir P. Barannikov

Thermal stability of polyvinyl alcohol/nanocrystalline cellulose composites.

Thermal stability of polyvinyl alcohol/cellulose nanocrystals (PVA/CNCs) composites prepared with solution casting technique was studied. The PVA/CNCs composites were characterized by Fourier transform infrared spectrometry, X-ray diffraction, differential scanning calorimeter (DSC) and thermogravimetric (TG) analysis. Due to the presence of CNCs nanoparticles, thermal degradation of the composites occurs at much higher temperatures compared to that of the neat PVA. Thermal stability of the PVA/CNCs composites is maximally enhanced with CNCs content of 8-12 wt%. Some thermal degradation products of the PVA/CNCs composites were identified by mass spectrometric analysis. TG measurements with synchronous recording of mass spectra revealed that the thermal degradation of both CNCs and PVA in the composites with CNCs content of 8-12 wt% occurs simultaneously at a much higher temperature than that of CNCs or the neat PVA. However, with increasing CNCs content more than 12 wt% the thermal stability of the composites decreases. In this case, the degradation of CNCs comes first followed by the degradation of PVA.

Thermochemical characteristics of the near surroundings of tetraphenylporpffln in benzene, pyridine and carbon tetrachloride

Abstract A new approach which allows the solvation surroundings of macrocyclic molecules to be simulated is proposed on the basis of thermogravimetric data. For the first time the compositions are determined of saturated solvates of tetraphenylporphin (H 2 TPP) with benzene, pyridine and carbon tetrachloride: H 2 TPP· 16C 6 H 6 , H 2 TPP· 18C 5 H 5 N and H 2 TPP·16CCl 4 . The energetic parameters of the interparticle interactions in the near solvation surroundings of H 2 TPP are characterized. A method is proposed for the evaluation of the change in enthalpies of solvation of macrocyclic molecules based on the values of the heats of evaporation.

Correlation of enthalpic and volume characteristics of 15-crown-5 in solution with molecular parameters and physical properties of solvents

Abstract The solution and solvation enthalpies at infinite dilution of 15-crown-5 in different organic solvents and water were measured. The limiting partial molar volumes of the crown ether in a series of solvents studied were determined using experimental density data. On the basis of the scaled particle theory the satisfactory multiparameter correlation of the quantities measured with properties of solvents was obtained. The known equations as modified by the introduction of more accurate radial distribution function g 12 ( r ) were used.

An investigation of the structural and thermodynamic properties of polystyrene fullerene-containing films

Polystyrene films doped with small additives of fullerenes (w = 0–1 × 10−3) are obtained. The nonmonotonic dependence of the glass transition point on composition with a minimum at w = 1 × 10−4 is revealed by the DSC method. It is concluded that there is a plasticizing action of small amounts of filler at w < 1 × 10−4 and domination of the effect of intermolecular interactions of fullerene with polystyrene at w > 1 × 10−4. It is established by small-angle X-ray scattering that composites containing fullerenes in the amount w > 1 × 10−4 are characterized by the greatest mobility of the segments in the modified polymer chains.

Crystal solvates of zinc(II) bis(dipyrrinates) with triethylamine: composition, stability and spectral-luminescent properties

Abstract Crystal solvates of 2,2′-, 2,3′- and 3,3′-bis(dipyrrinato)zinc(II) with triethylamine (TEA) were obtained by slow crystallization. Composition, structural organization, stability, and spectral-luminescent properties of the crystal solvates were studied by FTIR, Powder X-ray Diffraction, thermal, mass spectral, absorption and fluorescence analyses. The thermal dissociation processes of crystal solvates in an argon atmosphere have been investigated. It is shown that zinc(II) helicates with decamethylsubstituted 2,2′-, 2,3′-, and 3,3′-bis(dipyrrin)s with TEA form stable supramolecular complexes of the composition [Zn2L2(TEA)4] and [Zn2L2TEA]. Spectroscopic studies showed that the quantum yield (φ) of [Zn2L2(TEA)n] crystal solvates in cyclohexane is noticeably (3–4.5 times) lower than φ of [Zn2L2] complexes. Quantum chemical study indicated the most likely mechanism for the coordination of solvent molecules on the coordinating centers of [Zn2L2]. Thermal and energy stability of [Zn2L2(TEA)n] solvates reduced when replacing the 2,2′- on 2,3′-, and 3,3′-isomer. The obtained results are of interest for the development of [Zn2L2] fluorescent sensors of the electron donor molecules.