Effect of 1-Pentanol on the Thermodynamics of the Micellization of Hexadecyltrimethylammonium Bromide in Aqueous Solutions

Russian Journal of Physical Chemistry A - The thermodynamic parameters (ΔH, ΔG, and ΔS) of the micellization of hexadecyltrimethylammonium bromide (CTAB) in aqueous solutions of...     

Extracting hydrocarbons from water using a centrifuge

An original method for the solid-phase microextraction of hydrocarbons from water using a centrifuge is proposed. Comparative results from the chromatographic elution of substances after liquid-phase and solid-phase microextraction are presented. The percentage of the extraction of substances from aqueous solutions and the minimum detection limit for aromatic and aliphatic compounds are calculated.     

Water vapor as a carrier gas in capillary gas chromatography

The use of water vapor as carrier gas in capillary chromatography is analyzed. Under equivalent conditions, a comparison of water vapor and helium as a mobile phase was performed during the separation of diesel fuel components. The advantage of water vapor was demonstrated. The resolutions of peaks were calculated for a pair of substances, C₁₈-iso and C₂₀ (4.4 for water vapor and 3.9 for helium). The Van Deemter dependences were measured, and it was demonstrated that the substantially lower viscosity of the water vapor compared to helium makes it possible to perform the separation of substances in a broader range of linear velocities, comparable to hydrogen used as mobile phase. The prospects for using water vapor was demonstrated in chromatographic analysis of hydrocarbons.     

Effect of Urea on the Thermodynamics of Hexadecyltrimethylammonium Bromide Micelle Formation in Aqueous Solutions

The effect of urea on the thermodynamics of hexadecyltrimethylammonium bromide (CTAB) micelle formation in aqueous urea solutions was studied by isothermal titration microcalorimetry. The thermodynamic functions of ΔH, ΔG, and ΔS of CTAB micelle formation were calculated. The critical micelle concentrations (CMC) were determined. The addition of urea to the solution decreased the micelle formation entropy. This was attributed to the “lowering” of the structural temperature of the solution, which led to an increased number of hydrogen bonds and structure formation of water.

     

Studies of the enthalpy relaxation and the “multiple melting” behavior of semicrystalline poly(arylene ether ether ketone) (PEEk)

We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes in the amorphous phas e of semicrystalline PEEK — enthalpy relaxation below the glass transition (T _g) and secondary crystallization aboveT _g. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer — the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained from small strain creep studies of physical aging of semicrystalline PEEK below and aboveT _g.We gratefully acknowledge support of this work by the National Science Foundation, Science and Technology Center for High Performance Polymeric Adhesives and Composites under DMR grant 91-2004 and by an NSF Young Investigator Award (DMR 93-57512).     

Heats of sorption of nuclear-spin isomers of water on activated carbon

Classical chromatographic measurements with the use of a nonselective thermal-conductivity detector were performed to determine the heats of sorption of the ortho and para spin-isomers of water on SKT activated carbon: Q _ortho = ?38.9 kJ/mol and Q _para = ?46.8 kJ/mol, as compared to published values of the overall heat of sorption of water on carbon adsorbents of 40–45 kJ/mol.     

Electrometric titrations of Cr(VI), Mn(IV), V(V), Co(III) and U(VI) with a standard iron(II) solution in alkaline media containing hexitols

Direct and indirect potentiometric, bipotentiometric and biamperometric titrations with a standard iron(II) solution are described for some inorganic compounds in alkaline media containing hexitols (mannitol, dulcitol and sorbitol). The optimal conditions for titrations based on the Cr(VI) → Cr(III), Mn(IV) → Mn(III) → Mn(II), V(V) → V(IV), Co(III) → Co(II) and U(VI) → U(IV) systems are discussed. Of the hexitols studied, sorbitol has the greatest effect on the value of the redox potential of the Fe(III)/Fe(II) system; the E_f° value is about —1.10 V vs. SCE.