Standard potentials of the silver/silver-iodide electrode in aqueous mixtures of ethylene glycol at different temperatures and the thermodynamics of transfer of hydrogen halides from water to glycolic media

The standard potentials (E°) of the silver/silver-iodide electrode in aqueous mixtures of ethylene glycol (containing 10, 30, 50, 70 and 90 wt-% glycol) have been determined from emf measurements of the cell Pt, H₂(g, 1 atm)/HOAc(m₁), NaOAc(m₂), Kl(m₃), solvent/AgI/Ag at nine temperatures ranging from 5 to 45°C. These E° values have been utilized to compute free energy (Δt_t°), entropy (ΔS_t°) and enthalpy (ΔH_t°) changes accompanying the transfer of HI from water to each of the solvents. These values as well as those for HCl and HBr and obtained earlier have also been utilized to evaluate ΔS_t°(i) for individual ions by a method of ‘simultaneous extrapolation,’ which in turn furnished the values of ΔH_t°(i) for these ions. These quantities and also the ‘chemical’ contributions for the halide ions as obtained by subtracting the ‘electrostatic’ contribution computed with the Born equation, have been examined in the light of ion—solvent interactions as well as the structural changes of the solvents. The observed results conform with what is expected from the competitive effects of the preferential solvating capacities of water towards halide ions and that of other solvents towards hydrogen ions, and also of the effects arising from the structural changes of the solvents that are likely to occur in the over-all transfer process.     

Solutions of benzoic acid in formamide—II. thermodynamic properties from electromotive force measurements

The emf of the cell Pt, H₂, HBz(m), Hg₂Bz₂, Hg in formamide has been measured at 5°C intervals over the temperature range 5–45°C. The values of the standard potentials of the mercury—mercurous benzoate electrode can be fitted in the form of equation, obtained by using the least squares method:

The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reaction have been evaluated for different temperatures.     

Selective adsorption of L-TA/D-TA by β-cyclodextrin derivative modified with l-tryptophan: Isotherm,kinetic and thermodynamics studies

β-Cyclodextrin derivative modified with l-tryptophan (L-Trp-CD) was prepared for recognitive chiral separation of tartaric acid enantiomers from ethanol solution. Kinetic properties were successfully investigated by pseudo-first-order model and pseudo-second-order model. Equilibrium data were described by the Langmuir and Freundlich isotherm models. The thermodynamics parameters (positive values of ΔH° and ΔS°, negative values of ΔG°) indicated that binding system for L-Trp-CD was endothermic, entropy gained and spontaneous. Selective adsorption result of l-tartaric acid (L-TA)/d-tartaric acid (D-TA) by L-Trp-CD indicated that L-Trp-CD has significantly higher adsorption capacity for L-TA compared with D-TA, and the selectivity coefficient is 3.36.     

Thermodynamics of the silver—silver chromate electrode in water + 10, + 20, + 30 and + 40 mass percent of dioxane at different temperatures

The emf of the cell: Ag, AgCl, NaCl(m)?Na₂CrO₄(m/2), Ag₂CrO₄, Ag in water + 10, + 20, + 30, and + 40 mass percent of dioxane has been measured at 5°C intervals over the temperature range 15–45°C. The values of the standard potentials of the silver—silver chromate electrode have been determined in these mixed solvent media at these temperatures. The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reaction in water + dioxane mixtures have been evaluated at these temperatures. The results are discussed in terms of the preferential solvation of the ions.     

Uptake of aromatic solvents by polyethylene films

The sorption properties of the solvents benzene, toluene, and xylene in polyethylene films at 40, 60, and 80°C were investigated. The diffusion coefficient increased with an increase in the sorption temperature for the solvents and was highest for xylene and least for benzene. The inability of xylene to show a definite order of the diffusion coefficients at the investigated temperatures was attributed to the presence of two methyl side groups in the molecule. The solubilities of the solvents in polyethylene increased with an increase in the sorption temperature, and the following order of the solubilities could be observed: xylene > toluene > benzene. The permeabilities of the solvents in polyethylene depended on the sorption temperature, and the following order of the permeabilities was observed: xylene > toluene > benzene. The calculated activation energies of sorption in polyethylene films were all positive; benzene had the highest energy of sorption, and xylene had the lowest. The calculated enthalpies of sorption (ΔH_S) were also positive for the three solvents and were in the following order: xylene > toluene > benzene. The calculated entropies of sorption (ΔS) were negative for the solvents and showed trends similar to the variation of ΔH_S among the solvents. The change in the Gibbs free energies of sorption (ΔG_S), evaluated with the expression ΔG_S = ΔH_S ? TΔS (where T is the Kelvin temperature), were all positive, and this was an indication of the nonspontaneity of the solubility of polyethylene in the aromatic solvents at 313 K. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3849–3854, 2007     

Equilibrium bulk polymerization of 1,3-dioxolan

Cationic bulk polymerization of 1,3-dioxolan has been carried out in sealed ampoules using a high vacuum technique. The polymerization is initiated with triethyl oxonium hexafluorophosphate and the equilibrium between monomer and active polymer is attained within a few hours. Specific volumes of pure monomer and polymer in solution of its own monomer have been measured. Equilibrium measurements have been performed in the 40° to 141·4°C temperature range and the ceiling temperature is estimated to be 144° ± 2°C. The effect of short polymer chains on the equilibrium is discussed briefly. Values of ΔG_lc, the free energy of polymerization of one mole of pure liquid monomer to one base-mole of amorphous polymer, are computed making allowance for the non-ideal mixing. Respective values of ?17.5 ± 0.8 kJ/mol and ?47.9 ± 2.2JK^?1mol^?1 are deduced for the corresponding ΔH_lc and ΔS_lc. ΔG_lc is also computed from published data on equilibrium polymerization of 1,3-dioxolan in various solvents and the combined results for both types of polymerization yield ΔH_lc = ?16.7 ± 0.5kJ/mol and ΔS_lc = ?45.8 ± 1.5JK^?1mol^?1 for the 20° to 140°C range.     

Experimental determination of the thermodynamic parameters affecting the adsorption behaviour and dispersion effectiveness of PCE superplasticizers

For adsorption of three different allylether-based PCE superplasticizers on CaCO₃ surface, the thermodynamic parameters ΔH, ΔS and ΔG were determined experimentally. The GIBBS standard free energy of adsorption ΔG_0ads, the standard enthalpy of adsorption ΔH_0ads and the standard entropy of adsorption ΔS_0ads applying to an unoccupied CaCO₃ surface were obtained via a linear regression of ln K (equilibrium constant) versus 1 / T (VAN'T HOFF plot). Additionally, the thermodynamic parameters characteristic for a CaCO₃ surface loaded already with polymer (isosteric conditions) were determined using a modified CLAUSIUS-CLAPEYRON equation.For all PCE molecules, negative ΔG values were found, indicating that adsorption of these polymers is energetically favourable and a spontaneous process. Adsorption of PCEs possessing short side chains is mainly instigated by electrostatic attraction and a release of enthalpy. Contrary to this, adsorption of PCEs with long side chains occurs because of a huge gain in entropy. The gain in entropy results from the release of counter ions attached to the carboxylate groups of the polymer backbone and of water molecules and ions adsorbed on the CaCO₃ surface. With increased surface loading, however, ΔG_isosteric decreases and adsorption ceases when ΔG becomes 0. The presence of Ca²⁺ ions in the pore solution strongly impacts PCE adsorption, due to complexation of carboxylate groups and a reduced anionic charge amount of the molecule. In the presence of Ca²⁺, adsorption of allylether-based PCEs is almost exclusively driven by a gain in entropy. Consequently, PCEs should produce a strong entropic effect upon adsorption to be effective cement dispersants. Molecular architecture, anionic charge density and molecular weight as well as the type of anchor groups present in a superplasticizer determine whether enthalpy or entropy is the dominant force for superplasticizer adsorption.     

The polycondensation of lithium 11–bromoundecanoate in aqueous media

To obtain a biodegradable plastic, polycondensation, the substitution of bromine by carboxylate was carried out on lithium 11–bromoundecanoate. Using water as a solvent, the formation of a double bond was detected between 70 and 100°C, yielding a good quantity of polymer. Water is recommended as the best solvent for the reaction. Thermodynamic investigations were carried out by using ethylene glycol and water. The reaction is believed to proceed according to the S_N2 mechanism. The ΔH and ΔG values for condensation in ethylene glycol were slightly higher than for those in water, but the reaction rate in water at 70°C was 7 times greater than that in ethylene glycol. The enhancement of dissociation accounts for the advantageous condensation in aqueous media. Furthermore, ΔS shows negative values and ΔG shows positive values, meaning that the reaction should proceed exothermically and not spontaneously. Experiments to condense 11–bromoundecanoate in aqueous media were carried out for ten days in a water bath, kept at 70°C, using 25 mL of 0.05M 11–bromoundecanoate. The degree of polymerization for the resulting polymer was found to be 23 by the end group assay for both bromine and carboxylate. Neither a melting point nor glass transition point for the product were observed. The polymer formed decomposes at 300°C and instantly disperses. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 130–134, 2003     

Solutions of iodic acid in formamide. Thermodynamic properties from electromotive force measurements

Electromotive force measurements on cells without liquid junction have been used to determine pK_a of iodic acid and the standard electrode potentials (E°) of the silver-silver iodate electrode in formamide at 9 temperatures from 5–45°C. The pK_a was evaluated by using the Debye-Huckel theory with an ion-size parameter of 5.5 A°. The change in the standard electrode potentials is given as a function of temperature, t°C by the equation E°_t = 0.2786 - 8.125 x 10^?4(t - 25) - 6.385 x 10^?6(t - 25)² The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reactions have been evaluated for different temperatures.     

Thermodynamics of micellization of poly-styrene-block-poly(ethylene/propylene) copolymers in decane

Light scattering was used to establish the dependence of the critical micelle temperature, CMT, on concentration for solutions of three polystyrene-block-poly(ethylene/propylene) copolymers in decane. Electron microscopy studies of particles isolated from the solutions showed that the micelles had narrow size distributions and micellization could be treated thermodynamically as a closed association. The light scattering results were used to calculate the standard Gibbs energies of micellization, ΔG^φ, and the standard enthalpy, ΔH^φ, and entropy contributions, —TΔS^φ. The values of ΔH^φ were large and negative, and markedly dependent on the molecular weight of the polystyrene block. The values of ΔG^φ for the three samples were on the other hand very similar to each other. The standard entropy contributions were unfavourable to micelle formation.     

Taming the Beast: Measurement of the Enthalpies of Combustion and Formation of Triacetone Triperoxide (TATP) and Diacetone Diperoxide (DADP) by Oxygen Bomb Calorimetry

Low‐melting paraffin wax was successfully used as a phlegmatizing agent to perform semi‐micro oxygen bomb calorimetry of spectroscopically pure samples of the sensitive explosive peroxides TATP and DADP. The energies of combustion (Δ_cU) were measured and the standard enthalpies of formation (Δ_fH°) were derived using the CODATA values for the standard enthalpies of formation of the combustion products. Whilst the measured Δ_fH° of DADP (Δ_fH°=−598.5 ± 39.7 kJ mol⁻¹) could not be compared to any existing literature value, the measured Δ_fH° value of TATP (Δ_fH°=+151.4 ± 32.7 kJ mol⁻¹) did not correlate well with the only existing experimental value and confirmed that TATP is an endothermic cyclic peroxide.     

Equilibrium,kinetics, and thermodynamics of Pd(II) adsorption onto poly(m‐aminobenzoic acid) chelating polymer

This study describes the equilibrium, kinetics, and thermodynamics of the palladium(II) (Pd(II)) adsorption onto poly(m‐aminobenzoic acid) (p‐mABA) chelating polymer. The p‐mABA was synthesized by the oxidation reaction of m‐aminobenzoic acid monomer with ammonium peroxydisulfate (APS). The synthesized p‐mABA chelating polymer was characterized by FTIR spectroscopy, gel permeation chromatography (GPC), thermal analysis, potentiometric titration, and scanning electron microscopy (SEM) analysis methods. The effects of the acidity, temperature, and initial Pd(II) concentration on the adsorption were examined by using batch adsorption technique. The optimum acidity for the Pd(II) adsorption was determined as pH 2. In the equilibrium studies, it was found that the Pd(II) adsorption capacity of the polymer was to be 24.21 mg/g and the adsorption data fitted better to the Langmuir isotherm than the Freundlich isotherm. The kinetics of the adsorption fitted to pseudo‐second‐order kinetic model. In the thermodynamic evaluation of the adsorption, the ΔG° values were calculated as ?16.98 and ?22.26 kJ/mol at 25–55°C temperatures. The enthalpy (ΔH°), entropy (ΔS°), and the activation energy (E_a) were found as 35.40 kJ/mol, 176.05 J/mol K, and 61.71 kJ/mol, respectively. The adsorption of Pd(II) ions onto p‐mABA was a spontaneous, endothermic, and chemical adsorption process which is governed by both ionic interaction and chelating mechanisms. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42533.     

Kinetics of thermal inactivation of transglutaminase from a newly isolated Bacillus circulans BL32

BACKGROUND: This paper describes the modeling of the kinetics of thermal inactivation of transglutaminase (TGase) from a newly isolated Bacillus circulans BL32, isolated from the Amazon environment. The purified enzyme was incubated at temperatures ranging from 30 to 70 °C and values of the thermodynamic inactivation parameters, such as activation energy (ΔE), activation enthalpy (ΔH), activation entropy (ΔS), and free energy (ΔG) for thermal inactivation, were calculated. RESULTS: The kinetics of TGase thermo‐inactivation followed a Lumry–Eyring model. The enzyme was very stable up to 50 °C, with approximately 50% of activity remaining after heating for 12 h. It was completely inactivated by incubation at 70 °C for 2 min. ΔE for TGase was 350.5 kJ mol^?1. ΔH and ΔS for thermo‐inactivation of the TGase were 347.8 kJ mol^?1 and 744 J mol^?1 K^?1 at 50 °C, respectively. Dynamic light scattering measurements suggest that the thermal inactivation of this microbial TGase can be partially attributed to the formation of aggregates. CONCLUSION: These results provide useful information about the thermal characteristics of the microbial TGase from B. circulans BL32 and indicate that this enzyme could be a good candidate for industrial applications. Copyright © 2009 Society of Chemical Industry     

A New Approach to the Dissolution Tests Management to Obtain Kinetic and Thermodynamic Data: Release of a Model Drug from Glyceryl Behenate Matrix Tablets

This study is focused on the use of glyceryl behenate as a lipophilic excipient of matrix tablets providing controlled drug release. The aim of this study is to evaluate activation energy (EA) and changes of the thermodynamic parameters (ΔH, ΔS, ΔG) of a dissolution process. These values, which have not yet been published, can lead to better understanding of a drug release mechanism and can extend the use options of glyceryl behenate in the pharmaceutical industry. Values of ΔH, ΔS, ΔG and E_A, providing an overall thermodynamic view on the studied matrix tablets, are evaluated based on the temperature-dependences of the release rate constant of a model drug (temperature range 25 - 45 °C). The studied lipophilic matrix tablets contain 10% to 50% of glyceryl behenate. Dissolution testing is carried out in an aqueous solution of HCl with addition of NaCl (pH1.2). Positive values of ΔH in the range of 3.83 to 56.13 kJ mol^-1 and positive values of ΔG indicate that the dissolution of the studied glyceryl behenate matrix tablets is an endothermic process which does not proceed spontaneously (in a temperature range of 25 - 45 °C). The negative slope of the linear curves of enthalpy-entropy compensation confirms the entropy-driven dissolution. Practical Applications : A better understanding of the dissolution process is an important aspect, e.g., in the field of drug formulation strategy. In this study, it is confirmed that the influence of temperature on the model drug release rate is negligible for tablets containing more than 40% of glyceryl behenate. It is an important result for drug design due to the reduction of risk of a possible dose dumping effect induced by temperature and the prevention of in vivo therapeutic failure.     

A thermodynamic study of the binding of human serum albumin onto N,N′‐diethylaminoethyl dextran microbeads

Adsorption of proteins on solid surfaces is widely studied because of its importance in various biotechnological, medical, and technical applications, e.g., biosensors, cardiovascular implants, and chromatography. Adsorption thermodynamics has been studied on the microbeads of N,N′‐diethylaminoethyl (DEAE) Dextran anion exchanger for the human serum albumin (HSA) at 25, 30, 35, 40, and 45°C. As a result, some thermodynamic parameters like Freundlich constants, thermodynamic equilibrium constant (K_D), standard free energy changes (ΔG_assoc), standard entropy changes (ΔS_assoc), and standard enthalpy change (ΔH_assoc) have been evaluated. Using the linear Van't Hoff plot, ΔH_assoc value of the system for the interaction of bovine serum albumin (BSA)‐adsorbed crosslinked DEAE dextran microbeads was determined as 20.650 kJ/mol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3942–3947, 2006     

Comparison of Water Absorption and Mechanical Behaviors of Polypropene Composites Filled with Rice Husks Ash

Composite materials were obtained by filling polypropene with raw and thermally treated rice husks at filler contents from 1 to 20%. The physicochemical properties were determined. A slight increase was observed in the tensile strength of the composites based on white rice husk ash (WRHA) and aerosil (AR) at degree of filling up to 3%. Young's modulus increased and the elongation at break and energy to break point showed a tendency to decrease for all the composites studied. The thermodynamics and kinetics of water absorption at immersion were studied in the temperature interval 25–90°C. The values of the changes in standard free energy, ΔG°, enthalpy, ΔH°, and entropy, ΔS° of adsorption were calculated. Water absorption was found to be thermodynamically difficult due to the diffusion mechanism of the process and it was accompanied by a decrease in the values of ΔH° and ΔS° with an increase in fillers contents. The effects of the amount of absorbed water, temperature, and treatment time on the composites tensile properties were estimated.     

Haematoxylin sorption onto yak hair: kinetic and thermodynamic studies

The kinetic and thermodynamic behaviours of haematoxylin sorption onto yak hair as a model system were investigated. It was found that the sorption kinetics of haematoxylin on hair followed a pseudo‐second‐order kinetic model. The equilibrium sorption capacity increased as the temperature increased from 303 to 313 K, but dropped gradually as the temperature increased beyond 313 K. The maximum equilibrium sorption capacity was 24.04 mg g^?1 at T = 313 K. Meanwhile, the sorption isotherm data were ingood agreement with the Freundlich isotherm, presenting high coefficients (R² > 0.99). The free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) terms for haematoxylin dyeing were also determined, the negative values of ΔG and ΔH obtained indicated that the haematoxylin dye sorption process is a spontaneous and an exothermic one. Also, positive values of ΔS showed an increase in disorder of the system of haematoxylin sorption onto hair. Haematoxylin could be a good candidate as a natural green dye for hair fibre.     

The graphite-sulfate lamellar compounds—I: Thermodynamic properties,new data

The fractional and total thermodynamic values ΔG°, ΔH° and ΔS° are calculated for the electrochemical formation of various stage graphite hydrogenosulfates (GHS) from pyrographite and 18 MH₂SO₄, based on emf measurements of the GHS/18MH₂SO₄/Hg₂SO₄/Hg cell. The disagreement between our results and the previous work of Aronson et al. is explained.     

Thermodynamic aspects of the bovine serum albumin adsorption onto N,N′‐ diethylaminoethyl dextran microbeads

Adsorption of proteins on solid surfaces is widely studied because of its importance in various biotechnological, medical, and technical applications, e.g., biosensor cardiovascular implants and chromatography. Adsorption thermodynamics has been studied on the microbeads of N,N′‐diethylaminoethyl (DEAE) dextran anion exchanger for bovine serum albumin at 25, 30, 35 40, and 45°C. As a result some thermodynamic parameters like Freundlich constants, thermodynamic equilibrium constant (K_D), standard free energy changes (ΔG_assoc), standard entropy changes (ΔS_assoc), and standard enthalpy change (ΔH_assoc) have been evaluated. Using the linear Van't Hoff plot, the ΔH_assoc value of the system for the interaction of BSA adsorbed crosslinked DEAE dextran microbeads was determined as 12.5 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Investigation of Biobased and Petroleum Base Oils in the Entire Spectrum of Lubrication Regimes

The tribological properties of biobased and petroleum-based base oils in the entire lubrication regime were investigated. High oleic sunflower oil (HOSuO) and commercially available polyalphaolefin (PAO-6) were selected to represent biobased and petroleum-based base oils, respectively. These two oils had similar viscosity and pressure-viscosity coefficient at 40 °C, but differed in their chemical structures and many other properties. Tribological tests were conducted on a high frequency reciprocating rig tribometer at 40 and 75 °C, for 60 min, 1000 gf load, and variable combinations of frequency and stroke length. Lubrication regimes were quantified using the Hersey number (H) which was calculated from lubricant viscosity and test parameters (load, frequency, stroke length). The key tribological test outputs were coefficient of friction (COF); film thickness (h) expressed in % from contact resistance measurement; and ball wear scar diameter (WSD). Analysis of experimental data showed that the biobased HOSuO provided lower COF, thicker lubricant film, and lower WSD than the petroleum-based PAO-6, in all lubrication regimes and at both temperatures (40 and 75 °C). The difference in these properties between the two oils, [Δ(COF), Δ(WSD), Δ(h)], were the greatest in the boundary regimes (low H values) where the polar chemical structure of the biobased lubricant played a dominant role.