Features of colloidal disperse structure formation in petroleum bitumen

Temperature-modulated differential scanning calorimetry has been employed to analyze the structure-related thermal properties of petroleum bitumen. This method enables one to distinguish between “order–disorder” and glass transitions, thereby making it possible to monitor and identify structure-related phase transformations, the signals from which are invisible or overlapped in the thermograms of conventional differential scanning calorimetry. Bitumen has been shown to be a colloidal disperse system only under certain temperature–time conditions. Its dispersed phase may be represented by aggregates of two types with colloidal sizes. Saturated hydrocarbons form a solid crystalline phase in accordance with the regularities of first-order structural phase transitions and nucleation mechanism of phase separation. Asphaltenes and resins form a solid amorphous phase for a relatively long time as a result of a structural relaxation glass transition by the spinodal mechanism of phase separation.     

Thermal and structural characterization of bitumen by modulated differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry - This paper presents the results of investigation of model bitumens, prepared by mixing of individual fractions of bitumen (saturates, aromatics, waxes,...     

Water-soluble proteins as an excipient for drug administration by inhalation

Microspherical particles of composite drugs based on lysozyme and albumin, which can be used in inhalation administration, were prepared by spray drying. The composition of the complexes was determined using experimental and theoretical methods. The use of the protein matrix makes it possible to increase the dissolution rate of the drug in water. The obtained results can be useful for the development of new drug dosage forms with increased bioavailability.

     

Rheological properties of epoxy oligomers and their mixtures in a wide temperature range

The rheological properties of a series of epoxy-diane and epoxy-novolac oligomers and active diluents were studied in a wide temperature range. The activation energies of their viscous flow in the regions of low and high temperatures were calculated. In a series of active diluents, the efficiency of decreasing viscosity of their mixtures with epoxy oligomers correlates with the glass transition temperature of the diluent.     

Molecular recognition of organic compounds by the data on polymorphic and pseudo-polymorphic transformations of tert-butylthiacalix[4]arene derivative

The receptor properties of metastable polymorphic forms of 5,11,17,23-tetra(tert-butyl)-25,26,27,28-tetrakis[N-(2-ethoxycarbonyl(methyl)carbamoylmethoxy]-2,8,14,20-tetrathiacalix[4]arene in the cone and partial cone configurations obtained by the crystallization of their solutions in an organic solvent were studied. The ability of the studied calixarenes to “remember” the history of interaction with individual vaporous organic guests and their mixtures was discovered. The observed different effects of methanol and ethanol vapors on the phase state of the studied calixarene in the cone configuration can be used for qualitative and quantitative analyses of ethanol in binary mixtures. Calixarene in the partial cone configuration can remember the earlier bound methanol. The “memory” effect appears as a specific polymorphic transition in the receptor phase after bound methanol leaving on heating the clathrate. This effect is not observed for other studied guests.     

Thermal analysis of charge-transfer complex formed by nitrogen dioxide and substituted calix[4]arene

Simultaneous thermal analysis with evolved gas analysis (STA-EGA) was used to study the ability of 1,3-alternate conformer of tert-butylcalix[4]arene with four n-propoxy substituents (1) to be applied for detection of nitrogen dioxide in reversible sensors. Solid calixarene 1 forms an intensively colored charge-transfer complex (CTC) with gaseous NO₂/N₂O₄. Using the STA-EGA method, the nature and conditions of CTC bleaching were characterized, including the conditions of its reversible change of color from white to dark blue and back at CTC formation and decomposition. For this, the thermal stability of CTC and its regeneration products were studied. This, together with the ion thermograms for evolved gases, gives the information on the oxidation of 1 by nitrogen dioxide if present.     

Molecular recognition of organic guest vapor by solid adamantylcalix[4]arene

A series of inclusion compounds prepared by saturation of the solid adamantyl[4]calixarene (host 1) with vaporous organic guests at 298 K was studied by thermal gravimetry and static headspace GC analyses. The sorption isotherms of guests by host 1, the stoichiometry of the guest—host inclusion compounds, and the Gibbs energies of their formation were determined. The data obtained give evidence of the molecular recognition of the guest shape by host 1. Hence, compound 1 can be used in sensors for recognizing volatile organic compounds with no strong hydrogen or donor-acceptor bonds involved.     

Structure-property relationship for clathrates formed in systems with guest vapor and 1,3-disubstituted <Emphasis Type="Italic">tert</Emphasis>-butylcalix[4]arene

Structure-property relationship was studied for a series of clathrates formed in the systems that model guest-host interactions on the surface of chemical odor sensors of quartz microbalance type. The clathrates of 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis(2-naphthylmethoxy)calix[4]arene (1) obtained by the saturation of its powder with gaseous organic compounds (guests) with the unity thermodynamic activity at 298 K were studied. The stoichiometry and temperature at the starting and ending points of thermal dissociation were determined for all the clathrates and stable intermediates by thermal gravimetric analysis. A sorption isotherm was determined for one guest-host combination; it indicates the formation of a stable clathrate in the system and phase transition of host upon reacting with guest. Decrease in thermal stability of the clathrates of 1 with guests of greater size was observed for studied pairs of homologous guests.