Kinetics of isothermal thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends

The thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends of different compositions was investigated by means of isothermal thermogravimetry in flowing atmosphere of synthetic air at temperatures 240–270 °C. The main degradation processes are dehydrochlorination of PVC and CPE. For calculation of the apparent activation energy and apparent pre-exponential factor two kinetic methods were used: isoconversional method and Prout–Tompkins method. True compensation dependency between Arrhenius parameters, obtained using Prout–Tompkins model, was found. Calculated kinetic parameters of isothermal thermooxidative degradation are close to those from non-isothermal degradation and confirm the assumption of the main degradation process in PVC/CPE blends.     

Computational and experimental study on the influence of the porogen on the selectivity of 4-nitrophenol molecularly imprinted polymers

In molecular imprinting the porogen plays a decisive role, as it not only affects the physical properties of the resulting polymer including its porosity, the specific surface area, and the swelling behavior, but also governs the stability of the prepolymerization complex, which in turn decisively determines the recognition properties of the resulting molecularly imprinted polymer (MIP).     

An Approximate Linear Solvation Energy Relationships Model Based on Snyder’s Selectivity Parameters. Chromatographic Behavior of Some 1-Aralkyl-4-Arylpiperazines

In order to elucidate the influence of the mobile phase composition on the retention of some 1-aralkyl-4-arylpiperazines, Snyder’s selectivity and polarity concept for building a simple linear solvation energy relationships model of chromatographic behavior was used. Maximum variability of mobile phase selectivity was achieved by using ternary mixtures of solvents from three different corners of the Snyder selectivity triangle: methanol as a strong proton donor, acetone as a strong proton acceptor and dimethyl formamide as a dipole interactor. Water was added to keep elution strength constant. Mobile phase composition was varied using Simplex–lattice mixture design. Selectivity parameters were calculated on the basis of linear relationships between volume fractions of pure solvents and their χ _e , χ _d , χ _n values. For seven-substituted 1-aralkyl-4-arylpiperazines R _M values were measured and correlated with previously calculated selectivity parameters. Mathematical models obtained are discussed according to the structural properties of the studied compounds.     

Silica-based composite and mixed-oxide nanoparticles from atmospheric pressure flame synthesis

Binary TiO₂/SiO₂ and SnO₂/SiO₂ nanoparticles have been synthesized by feeding evaporated precursor mixtures into an atmospheric pressure diffusion flame. Particles with controlled Si:Ti and Si:Sn ratios were produced at various flow rates of oxygen and the resulting powders were characterized by BET (Brunauer–Emmett–Teller) surface area analysis, XRD, TEM and Raman spectroscopy. In the Si–O–Ti system, mixed oxide composite particles exhibiting anatase segregation formed when the Si:Ti ratio exceeded 9.8:1, while at lower concentrations only mixed oxide single phase particles were found. Arrangement of the species and phases within the particles correspond to an intermediate equilibrium state at elevated temperature. This can be explained by rapid quenching of the particles in the flame and is in accordance with liquid phase solubility data of Ti in SiO₂. In contrast, only composite particles formed in the Sn–O–Si system, with SnO₂ nanoparticles predominantly found adhering to the surface of SiO₂ substrate nanoparticles. Differences in the arrangement of phases and constituents within the particles were observed at constant precursor mixture concentration and the size of the resultant segregated phase was influenced by varying the flow rate of the oxidant. The above effect is due to the variation of the residence time and quenching rate experienced by the binary oxide nanoparticles when varying the oxygen flow rate and shows the flexibility of diffusion flame aerosol reactors.     

Kinetic spectrophotometric determination of traces of molybdenum(VI) by its inhibitory effect on the oxidation of 4-hydroxycoumarine by potassium permanganate.

The present paper describes a simple, selective and sensitive kinetic method for the determination of trace amounts of molybdenum(VI) based on its inhibitory effect on the reaction oxidation of 4-hydroxycoumarine by KMnO(4) in the presence of hydrochloric acid, at pH 1.75 at 25 degrees C. The rate of the indicator reaction was followed spectrophotometrically by measuring the decrease in the absorbance of KMnO(4) at 525 nm. The development method includes optimization of the reagent concentration and temperature. The calibration graph was linear in the range of concentrations from 20 to 200 ng/cm(3) of molybdenum(VI). The probable relative error was in the interval 3.10 - 10.52% for the concentration range of 200 - 20 ng/cm(3) molybdenum(VI), respectively. The interference effects of the foreign ions were determined to assess the selectivity of the method. The developed method was found to have relatively good selectivity, sensitivity, simplicity and rapidity. The proposed method was applied to the determination of molybdenum(VI) in a particular type of steel and alloy (hastelloy).     

The effects of heating on mechanical loss in tantala/silica optical coatings

Second-generation interferometric gravitational-wave detectors will operate at temperatures noticeably above room temperature. Study was done to determine what effect elevated temperatures would have on the Q and coating thermal noise of the detector mirrors. Results show that increased temperature increases loss angle in a manner that is more significant at higher frequencies. Trends show that the increased temperature will have a negligible effect at the low (100 Hz) frequencies important to second-generation detectors.     

Water-hydrocarbon interfaces: effect of hydrocarbon branching on interfacial structure

Molecular dynamics simulation are performed for the water/hydrocarbon system to study the effect of hydrocarbon branching on interfacial properties. The following two series of hydrocarbons are considered: (1) n-pentane, 2-methyl pentane, and 2,2,4-trimethyl pentane (constant chain length) and (2) n-octane, 2-methyl heptane, and 2,2,4-trimethyl pentane (constant molecular mass). With a simple algorithm for identification of surface sites and mapping nonsurface sites to these surface sites, intrinsic profiles were constructed with respect to the surface layer. Intrinsic density profiles for water and hydrocarbons with respect to the hydrocarbon and water surface, respectively, resemble density profiles of liquids in the presence of a wall. Order parameters were used to study orientation of molecules with respect to the surface normal and the hydrogen bond network was characterized in terms of the number of hydrogen bonds per water molecule and percentage of hydrogen bonded molecules in the first coordination shell. The corresponding intrinsic profiles were obtained. The O-H bond for surface water was found to have two preferential orientations, pointing toward the hydrocarbon phase and parallel to the interface. Hydrocarbon molecules in series 1 orient along the interface with the more branched molecule better aligned. For molecules in series 2, the larger molecular length reduces the alignment of molecules along the interface.