Search results for "Efficient"
showing 10 items of 1603 documents
Effect of the reference solution in the measurement of ion activity coefficients using cells with transference at T=298.15K
2010
Abstract This work reports individual activity coefficients of ions at T = 298.15 K in aqueous solutions obtained from voltage values of the respective half-cell ion-selective-electrode and a single-junction Ag–AgCl reference electrode, filled with different reference solutions at different concentrations. For potassium and chloride ions in KCl aqueous solutions, reference solutions of KCl, NaCl, or CsCl were used. For sodium and chloride ions in aqueous NaCl solutions, reference solutions of CsCl were used. Experimental runs were performed at molalities (1, 2, and 3) m of the reference solution. The concentration of the sample solution was increased, starting from around 1 · 10−3 m, up to …
Energetics of sodium dodecylsulfate-dodecyldimethylamine oxide mixed micelle formation
1994
Enthalpies of dilution and osmotic coefficients of the sodium dodecyl-sulfate (NaDS)-dodecyldimethylamine oxide (DDAO) mixtures in water have been measured at 25 and 37°C, respectively. From the enthalpies of dilution the apparent molar relative enthalpies LΦ were calculated. The change of the LΦ vs. total molality mt profiles with the mole fraction reflects the variation of the ionic character of the mixed micelles. From the osmotic coefficients the nonideal free energy G2ni were calculated. By combining G2ni with the partial molar relative enthalpies, the nonideal entropies TS2ni were determined. At a given mole fraction, G2ni and TS2ni values are decreasing and increasing respectively, t…
Thermodynamic properties of N-octyl- and N-dodecylnicotinamide chlorides in water
1990
Densities, heat capacities and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for N-octyl- and N-dodecylnicotinamide chlorides in water over an extended concentration region. Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25°C were derived as a function of the surfactant concentration. For both surfactants, plots of volumes, enthalpies and free energies vs. concentration are regular whereas those of heat capacities and entropies present anomalies at about 0.8 and 0.1m for the octyl and dodecyl compounds, respectively. Changes in the slope of a plot of osmotic coefficients times molality vs. molality were…
Prediction of Maxwell – Stefan diffusion coefficients in polymer – multicomponent fluid systems
2014
Abstract Calculations of mass fluxes in multicomponent fluids based on the system of generalized Maxwell–Stefan equations (GMSE) is preferably used because Maxwell–Stefan (M–S) diffusion coefficients are symmetrical and have a clear physical meaning, as they reflect the binary friction forces between compounds in the system. For the calculation of the mass transport of a multicomponent fluid in the polymer basing on GMSE, it is necessary to have M–S diffusion coefficients. This paper proposes a method that allows their calculation using widely available self-diffusion coefficients and binary diffusion coefficients for infinitely diluted mixtures. The proposed method was compared with the me…
Modeling ATP protonation and activity coefficients in NaClaq and KClaq by SIT and Pitzer equations.
2006
Abstract The acid–base properties of Adenosine 5′-triphosphate (ATP) in NaCl and KCl aqueous solutions at different ionic strengths (0 I / mol L − 1 ≤ 5 for NaCl aq , 0 I / mol L − 1 ≤ 3 for KCl aq ) and at t = 25 °C were investigated. A selection of literature data on ATP protonation constants and on activity isopiestic coefficients was performed, together with new potentiometric measurements (by ISE-H + , glass electrode). Both literature and new experimental data were used to model the dependence on ionic strength and ionic medium of ATP protonation by SIT (Specific ion Interaction Theory) and Pitzer equations. In addition to values of first and second ATP protonation constants in…
Calculations of organic-solvent dispersions of single-wall carbon nanotubes
2005
The aqueous solubility Sw and 1-octanol–(Po), cyclohexane–(Pch), and chloroform–(Pcf) water partition coefficients are calculated. The properties of single-wall carbon nanotubes (SWNT) are related to the indices (n, m) designating the chiral vector. SWNTs are classified in zigzag (n, 0), armchair (n, n), and chiral (n, m). These properties permit classifying SWNTs according to (n, m). Correlations between (n2 + nm + m2)1/2, log Sw, log Po, log Pch, and log Pcf show that (n, m) are adequate indices. The (10,10) is the most abundant SWNT, presenting consistency between great kinetic stability, small Sw, and great {Po, Pch, Pcf}. The room temperature solubility of SWNTs is investigated in a va…
Isobaric Vapor−Liquid Equilibria of the Water + 2-Propanol System at 30, 60, and 100 kPa
1996
Isobaric vapor−liquid equilibria were obtained for the water + 2-propanol system at 30, 60, and 100 kPa. The activity coefficients were found to be thermodynamically consistent by the methods of Van Ness−Byer−Gibbs, Kojima, and Wisniak. The data were correlated with five liquid phase activity coefficient models (Margules, Van Laar, Wilson, NRTL, and UNIQUAC).
Binding of basic amphipathic peptides to neutral phospholipid membranes: a thermodynamic study applied to dansyl-labeled melittin and substance P ana…
1997
A thermodynamic approach is proposed to quantitatively analyze the binding isotherms of peptides to model membranes as a function of one adjustable parameter, the actual peptide charge in solution z(p)+. The main features of this approach are a theoretical expression for the partition coefficient calculated from the molar free energies of the peptide in the aqueous and lipid phases, an equation proposed by S. Stankowski [(1991) Biophysical Journal, Vol. 60, p. 341] to evaluate the activity coefficient of the peptide in the lipid phase, and the Debye-Huckel equation that quantifies the activity coefficient of the peptide in the aqueous phase. To assess the validity of this approach we have s…
A series expansion of the extended Debye-H�ckel equation and application to linear prediction of stability constants
1996
The Debye-Hückel semiempirical extended equation is frequently used to calculate activity coefficients of chemical species and equilibrium constants at ionic strengths different from those used in their experimental evaluation. A series expansion of the extended Debye-Hückel equation is proposed here and checked with experimental data taken from the literature. The expansion is linear in the ionic parameters and yields a geometrical series which converges rapidly and that enables the accurate calculation of interpolated and extrapolated activity coefficients and equilibrium constants by simple and multiple linear regression without previous knowledge of the ionic parameters.
Isobaric Vapor–Liquid Equilibria for the Extractive Distillation of Ethanol + Water Mixtures Using 1-Ethyl-3-methylimidazolium Dicyanamide
2011
Isobaric vapor–liquid equilibria (VLE) for the binary systems ethanol + 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) and water + [emim][DCA] as well as the VLE for the ternary system ethanol + water + [emim][DCA] have been obtained at 100 kPa using a recirculating still. The effect of [emim][DCA] on the ethanol + water system has been compared with that produced by another ionic liquid reported in the literature on the basis of the variation of solvent activity coefficients in ionic liquid (IL) + molecular solvent binary systems. From the results, [emim][DCA] appears as one of the best entrainers for the extractive distillation of the ethanol + water mixtures, causing the azeotrope…