Micellization of dodecyldimethylethyl- ammonium bromide in aqueous solution

Specific conductivity of aqueous solutions of dodecyldimethylethylammonium bromide has been determined in the temperature range of 15-40°C. The critical micelle concentration (cmc) and ionization degree of the micelles, b, were determined from the data. Thermodynamic functions, such as standard Gibbs free energy, ΔG _m°, enthalpy, ΔG _m°, and entropy, ΔG _m°, of micellization, were estimated by assuming that the system conforms to the mass action model. The change in heat capacity upon micellization, ΔG _m°, was estimated from the temperature dependence of ΔG _m°. An enthalpy-entropy compensation phenomenom for the studied system has been found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal parameters associated to micellization of dodecylpyridinium bromide and chloride in aqueous solution

Electrical conductivity of aqueous solutions of dodecylpyridinium chloride and bromide have been determined. From these data the critical micelle concentration (cmc) was determined. The thermal properties as standard Gibbs free energy, enthalpy and entropy of micellization was estimated from a uncharged-phase separation model and enables to obtain another properties like heat capacity of micellization and the relevant parameters in the minimum of temperature dependence of cmc. The enthalpy-entropy compensation was shown for the studied compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature dependence of second critical micelle concentration of dodecyldimethylbenzylammonium bromide in aqueous solution

The specific conductivity of dodecyldimethylbenzylammonium bromide (C12BBr) in aqueous solutions, in the temperature range of 15 to 40 °C, has been measured as a function of molality. The two breaks which were found on the conductivity against molality plots were attributed to the critical micelle concentration, cmc, and second critical micelle concentration, 2^nd cmc, respectively. The ratio of the slopes, S, of the three linear fragments on the plots, S2/S1 and S3/S1, was attributed to the degree of ionization of the micelles at cmc and 2^nd cmc respectively. It was shown that the values of the 2^nd cmc estimated above 27 °C are only apparent due to thermal disintegration of the micelles. In the temperature range of 15 to 27 °C, the values of the 2^nd cmc increase gradually and the plot of the 2^nd cmc against temperature is concave. The ratio of 2^nd cmc/cmc for C12BBr at 25 °C amounts to 15 and appears to be high compared to the literature values for other surfactants. For comparative purposes the cmc and 2^nd cmc values were also estimated conductometrically for decyldimethylbenzylammonium bromide (C10BBr) at 25 °C. The 2^nd cmc value for this surfactant is higher compared to the value for the C12 homologue by a factor of 2.6.The standard Gibbs free energies of micellization at cmc and at the 2^nd cmc were estimated from the experimental data for both surfactants at 25 °C.     

Influence of temperature on the micellization of sodium dodecylsulfate in water from speed of sound measurements

Speed of sound measurements for aqueous solutions of sodium dodecylsulfate (NaDS) have been carried out from 20 to 45°C at intervals of 5°C. The critical micellar concentrations (cmc) were determined and their change with temperature is discussed. A second change in the speed of sound has been found between 15 to 20mM for temperatures above 20°C. Values for G _m ^o , H _m ^o and S _m ^o for the micellization process have been determined and compared with data previously obtained from other experimental properties. These results confirm that the micellization process of NaDS in water is mainly entropically driven.     

Effect of counterion on thermodynamic micellar properties of tetradecylpyridinium in aqueous solutions

Electrical conductivity of aqueous solutions of tetradecylpyridinium bromide and chloride has been measured as a function of surfactant molal concentration and temperature. From the molal dependence of conductivity, the critical micelle concentration and the micellar ionization degree were estimated. The temperature dependence of these parameters has been used for calculating the thermodynamic parameters related with the micellization process by using the classical charged pseudophase separation model. The effect of the counterion on the conventional thermodynamic potentials of micellization such as standard Gibbs free energy, enthalpy and entropy has also been a matter of study. Finally, the occurrence of the enthalpy–entropy compensation phenomenon was verified and the relevant parameters discussed.     

电化学方法测定纳米材料的热力学函数

以纳米铜为例,首次采用电化学方法获取纳米材料的热力学函数.通过电化学沉积法制备了粒子尺寸约80nm的纳米铜电极,测定纳米铜与块体铜电极的电势差,以块体铜的热力学函数值为参考标准,根据纳米铜与块体铜的热力学关系式,求得纳米铜的标准摩尔生成焓、标准摩尔生成吉布斯自由能、标准摩尔熵分别为5.16kJmol-1、0.216kJmol-1、49.75JK-1mol-1,同时,求得纳米铜可逆电池反应的热效应为-4.95kJmol-1.     

Thermodynamics of the reaction between poly-1,1,2-trichlorobuta-1,3-diene and poly(ethylene imine) to form interpolymer

Thermodynamic parameters of the interpolymer reaction between poly-1,1,2-trichlorobuta1,3-diene and poly(ethylene imine) giving a polymer-polymer compound (incorporating the starting components in a molar ratio of 1 : 2) have been determined by calorimetry. The enthalpy (H°_m), entropy (S°_m), and Gibbs function (G°_m) for this reaction are negative over the whole temperature range studied. The enthalpy of the reaction in chloroform at 298.15 K is about two times smaller, due to the difference in the enthalpies of dissolution of the starting polymers and the enthalpy of swelling of the interpolymer in the same solvent. The glass transition temperature of the interpolymer lies between those of the starting polymers and coincides with the value calculated from the Fox equation. The heat capacity of the interpolymer is smaller than additive values calculated fromC _p ^° of the starting polymers. From the experimentally determinedC _p ^° for the polymers, the thermodynamic functionsC _p ^° (T),H°(T) – H°(O), andS°(T) were calculated for the 0–330 K temperature range, and their configurational entropiesS _c ^° were estimated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2474–2478, October, 1996.     

Solid-Solute Phase Equilibria in Aqueous Solution. XI. Aqueous Solubility and Standard Gibbs Energy of Cadmium Carbonate

The solubilities of CdCO₃ (otavite) in aqueous NaClO₄ solutions have been investigated as a function of ionic strength (0.15 I/mol-kg^–1 5.35, 25°C) and temperature (25°C T 75°C, I = 1.00 mol-kg^–1). A new Chemsage optimization routine was employed to simultaneously evaluate solubility data from this work and other sources, as well as standard electrode potentials determined at different ionic strengths. With the Pitzer equations the solubility constants, , were extrapolated to infinite dilution resulting in log and the ternary ion-interaction parameters ^S_Na,Cd = 0.19 and at 25°C. In addition, the following set of thermodynamic quantities can be derived from the present solubility data for otavite: _f G = –674.2±0.6 kJ-mol^–1; _f H = –755.3±3.4 kJ-mol^–1; S = 93±10 J-mol^–1K^–1. However, the present solubility data are also consistent with a recent determination of the standard entropy of otavite which leads to a recommended set of thermodynamic quantities [_f G (CdCO₃) = –674.2±0.6; _f H (CdCO₃) = –752.1±0.6; S (CdCO₃) = 103.9±0.2].     

Enthalpies of dilution from 50 to 225°C of aqueous decyltrimethylammonium bromide

Enthalpies of dilution of aqueous decyltrimethylammonium bromide have been measured from 0.56 to about .005 mol-kg^–1 and from 50 to 225°C near the saturation pressure of water using a flow calorimeter. The changes of the stoichiometric osmotic and activity coefficients with temperature, the excess apparent molar heat capacity, and the apparent and partial relative molar enthalpies have been calculated from the data.     

Predicted and experimental standard electrode potentials in liquid ammonia at 25°C

Methods are described for the prediction of standard Gibbs free energies of formation of monatomic and polyatomic ions in liquid ammonia at 25°C. Supplementation with auxiliary free energy data allows the tabulation of standard electrode potentials in 1 m acid liquid ammonia solutions for 143 half-reactions involving 58 elements.     

Thermodynamics of the Second Dissociation Constant and Standards for pH of 3-(NMorpholino) Propanesulfonic Acid (MOPS) Buffers from 5 to 55°C

The second dissociation constant pK2 of 3-(N-morpholino)propanesulfonic acid (MOPS) has been determined at eight temperatures from 5 to 55°C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver–silver chloride electrodes. The pK2 has a value of 7.18 ± 0.001 at 25°C and 7.044 ± 0.002 at 37°C. The thermodynamic quantities G°, H°, S°, and C _p ^o have been derived from the temperature coefficients of the pK ₂. This buffer at ionic strength I = 0.16 mol-kg^–1 close to that of blood serum, has been recommended as a useful secondary pH standard for measurements of physiological fluids. Five buffer solutions with the following compositions were prepared: (a) equimolal mixture of MOPS (0.05 mol-kg^–1) + NaMOPS, (0.05 mol-kg^–1); (b( MOPS (0.05 mol-kg^–1) + NaMOPS (0.05 mol-kg^–1) + NaCl (0.05 mol-kg^–1); (c) MOPS (0.05 mol-kg^–1) + NaMOPS (0.05 mol-kg^–1); + NaCl (0.11mol-kg^–1); (d) MOPS (0.08 mol-kg^–1) + NaMOPS (0.08 mol-kg^–1); and (e)MOPS (0.08 mol-kg^–1) + NaMOPS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1).The pH values obtained by using the pH meter + glass electrode assembly are compared with those measured from a flow–junction calomel cell saturated with KCl (cell B), as well as those obtained from cell (A) without liquid junction at 25 and 37°C. The conventional values of the liquid junction potentials E _j have been obtained at 25 and 37°C for the physiological phosphate reference solution as well as for the MOPS buffers (d) and (e) mentioned above.     

Thermodynamics of glycine solution in aqueous urea. Rule \sqrt m

The solution heats of glycine in aqueous urea have been determined by calorimetry at 298 K (molality 0–13) and 313 K (molality 0–22). The solution heat of the amino acid is described by the linear dependence of this quantity on the square root of the urea molality. The enthalpy, entropy, and Gibbs energy of the transfer of glycine from water to aqueous urea, as well as the heat capacity, entropy variation, and Gibbs energy of glycine solution have been calculated for the temperature range 273–323 K. It is found that urea additions to water reverse the sign of the heat capacity of solution.     

Surfactant ion electrode measurements of sodium alkylsulfate and alkyltrimethylammonium bromide micellar solutions

EMF measurements in water at 25°C have been made using surfactant ion and counterion electrodes on two homologous series of long chain surfactants, the sodium alkylsulfates (R=n-C₈H₁₇ to n-C₁₄H₂₉) and the alkyltrimethylammonium bromides (R=C₁₀H₂₁ to C₁₆H₃₃). The data show evidence of association below the critical micelle concentration (CMC) but not of micelle ordering due to coulombic repulsion above this concentration.     

The aggregation in dodecyltrimethylammonium hydroxide aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC _T=(2.51±0.10)×10^–4 mol · dm^–3 the surface excess becomes zero, atC _T=(1.300±0.041)×10^–3 mol · dm^–3 small aggregates from, which grow with concentration. AtC _T=(1.108±0.010)×10^–2 mol · dm^–3 true micelles form (CMC) and at (3.02±0.28)×10^–2 mol · dm^–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases.     

Thermodynamics of Polyvinylacetate from 0 to 350 K

The temperature dependence of the heat capacity of vinyl acetate in the range 13 to 330 K and of polyvinylacetate between 4.9 and 330 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. Temperatures and enthalpies of physical transitions were measured. From the data obtained, the thermodynamic characteristics of melting of vinyl acetate and parameters of glass transition and glassy state of the monomer and polymer were calculated. The thermodynamic functions H^o(T)-H^o(0), S^o(T), G^o(T)-H^o(0) were estimated for both materials from 0 to 350 K. The results of calculation and the literature value of enthalpy of bulk polymerization of vinyl acetate at T=350 K were used for the estimation of the thermodynamic parameters of its polymerization process ΔH_pol ^o, ΔS_pol ^o, ΔG_pol ^oin the interval 0 to 350 K. A ceiling limiting temperature of polymerization T_ceil ^owas evaluated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Micellization of Cationic Surfactant Cetyltrimethylammonium Bromide in Mixed Water-Alcohol Media

The effect of methanol, ethanol, and 1-propanol on cmc and degree of counter ion binding, β, of cetyltrimethylammonium bromide (CTAB) has been studied conductometrically. The micellization of CTAB in these water-alcohol media have been found to be both dependent on nature as well as the concentration of alcohol in water. The cmc values shift toward higher concentration with increase in alcoholic content up to certain concentration beyond which decrease in cmc is registered in case of all the alcohols. However, the maximum in the cmc versus concentration of alcohol shifts to lower concentration with the increase in number of carbons in alcohol. β shows the inverse peaked behaviour in conformity with the cmc variation. The effects viz. solvent modifying tendency of alcohols and their tendency of penetration into the micelles have been used to interpret their effect on micellization of CTAB.     

Enthalpy of dilution of aqueous sodium chloride from 76 to 225°C and aqueous dodecyltrimethylammonium bromide from 50 to 225°C

Enthalpies of dilution of aqueous sodium chloride from 3.0 to about 0.01 mol-kg^–1 have been measured from 349.2 to 498.2 K near the saturation pressure of water using a flow calorimeter. Enthalpies of dilution of aqueous dodecyltrimethylammonium bromide have been measured from 0.3 to about 0.005 mol-kg^–1 and from 323.4 to 498.3 K, also near the saturation pressure of water.     

Heat capacity of poly(vinyl methyl ether)

The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ₁ = 647 K, Θ₂ = Θ₃ = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by C_p(liquid) = 72.36 + 0.136 T in J K^?1 mol^?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing C_p of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005     

The sources of thermal energy exchange accompanying microbial anabolism

Calculations are made of the thermal energy exchanges accompanying the anabolism of Saccharomyces cerevisiae of four substrates using the equations and . Contrary to a previous postulate cited in the Discussion, the free-energy changes accompanying anabolism are not zero, but can be either positive or negative. However, their magnitude with either sign is small compared to that of catabolism of the same substrates, so that even with free energy changes that are negative it is unlikely anabolism can be considered a spontaneous process.     

Paradigms and Paradoxes: The Solubility of AgCl in Water: Some Thermochemical Issues of Aqueous Ag+ Ion

It is well established in the pedagogical literature that AgCl is insoluble in water while NaCl and KCl are soluble: applications of this difference are made in elementary studies of both qualitative and quantitative analysis. What is usually left unsaid, however, is why AgCl is so much less soluble than NaCl or KCl. This brief note addresses this issue in terms of the thermochemistry of these three metal chlorides and constituent ions as found in their solid salts, aqueous solutions and gaseous diatomic molecules.