Thermodynamics of binary mixtures: Volumes,heat capacities,and dilution enthalpies for then-pentanol+2-methyl-2-butanol system

The densities, heat capacities, and dilution enthalpies ofn-pentanol+2-methyl-2-butanol mixtures have been measured, in many cases as a function of temperature, over the complete mole fraction range. Excesses thermodynamic properties, apparent and partial molar heat capacities, volumes and expansibilities were derived. The concentration and temperature dependences of these functions are discussed in terms of the variations of the structure of the system caused by the participation of the two alcohol molecules (with quite different steric hindrance of the alkyl chain around the-OH group) in the dynamic intermolecular association process through hydrogen bonding.     

Volumes and heat capacities of mixtures of dimethylformamide with several dialkylacetamides

Densities and heat capacities per unit volume of binary mixtures of dimethylformamide and a series of di-n-alkylacetamides have been measured and converted into excess molar volumes and heat capacities of the mixtures. In addition, the apparent and partial molar volumes and heat capacities of the various components have been evaluated. They vary smoothly with the mole fraction. The apparent molar heat capacities in the mixtures depend linearly on volume fraction, so that the partial molar heat capacities can be described using only one parameter for each mixture.     

Volumetic Properties of Glycerol with N,N-Dimethylformamide and with Water at 25 and 35°C

Densities of glycerol + N,N-Dimethylformamide (DMF) and glycerol + water mixtures have been measured over the full range of compositions at 25 and 35°C. Excess molar volumes and excess partial molar volumes, of each system have been calculated. All mixtures show negative values of the excess molar volume due to increased interactions between unlike molecules.     

Volumetric Properties of N, N-Dimethylformamide with 1,2-Alkanediols at 20°C

Dilatometric measurements of excess molar volumes and excess partial molar volumes have been made for binary mixtures of N, N-dimethylformamide with 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 1,2- pentanediol, and 1,2-hexanediol at 20°C over the entire composition range. The results are explained in terms of dissociation of the self-associated 1,2-alkanediol molecules and the formation of aggregates between unlike molecules through C = O ... 3H-O hydrogen bonding. Further, the effects of difference in chain lengths and steric factors on molecular interactions are also examined. From the experimental results, excess molar volumes were calculated and correlated by a Redlich–Kister type function in terms of mole fractions.     

Volumes and heat capacities of water andN-methylformamide in mixtures of these solvents

The densities of mixtures ofN-methylformamide (NMF) and water (W) have been measured at 5, 15, 25, 35, and 45°C, and the heat capacities of the same system at 25°C, both over the whole mole-fraction range. From the experimental data the apparent molar volumes (_v) and heat capacities (_c) of NMF and of water are evaluated. The relatively small difference between the partial molar volumes or heat capacities at infinite dilution and the corresponding molar volumes or heat capacities of the pure liquids for both NMF and water suggests that with regard to these quantities replacement of a NMF molecule by a water molecule or vice versa produces no drastic changes. The partial molar volume of water at infinite dilution in NMF is smaller than the molar volume of pure water, but the corresponding partial molar heat capacity is unexpectedly high.     

Cobalt(II) chloro complexation in N-methylformamide–N, N-dimethylformamide mixtures

Cobalt(II) chloro complexation has been studied by titration calorimetry and spectrophotometry in solvent mixtures of N-methylformamide (NMF) and N,N-dimethylformamide (DMF). It revealed that a series of mononuclear CoCln_n ^(2–n)+ (n=1–4) complexes are formed in the mixtures of NMF mole fraction x _NMF=0.05 and 0.25, and the CoCl⁺, CoCl₃ ^– and CoCl₄ ^2– complexes in the mixture of x _NMF=0.5, and their formation constants, enthalpies and entropies were obtained. As compared with DMF, the complexation is markedly suppressed in the mixtures, as well as in NMF. The decreasing formation constant of CoCl⁺ with the NMF content is mainly ascribed to the decreasing formation entropy. DMF is aprotic and thus less-structured, whereas NMF is protic to form hydrogen- bonded clusters. In DMF-NMF mixtures, solvent clusters in neat NMF are ruptured to yield new clusters involving DMF, the structure of which depends on the solvent composition. The entropy of formation of CoCl⁺ will be discussed in relation to the liquid structure of DMF, NMF and their mixtures.     

Thermodynamics of liquid mixtures containing n-alkanes and strongly polar components: VE and C P E of mixtures with either pyridine or piperidine

Excess molar volumes V _E and excess molar heat capacities C _P ^/E at constant pressure have been obtained, as a function of mole fraction x₁, for several binary liquid mixtures belonging either to series I: pyridine+n-alkane (C_lH_2l+2), with l=7, 10, 14, 16, or series II: piperidine+n-alkane, with l=7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. V ^E of pyridine+n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x₁>0.90). All the other systems show positive V ^E only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine+n-heptane in the region rich in piperidine (x₁>0.87). The C _P ^/E at the respective minima, C _P ^/E (x_1,min ), become more negative with increasing l, and the x_1,min values range from about 0.26 (l=7) to 0.39 (l=14). Most interestingly, mixtures of series I exhibit curves of C _P ^/E against x₁ with two minima and one maximum, the so-called W-shape curves.Dedicated to Professor A. Néckel on the occasion of his 65^th birthday. Communicated in part at the XVII^èmes Journées de Calorimétrie, d'Analyse Thermique et de Thermodynamique Chimique, Ferrara, Italy, 27–30 October, 1986.     

Model systems for hydrophobic interactions: Volumes and heat capacities ofn-alkoxyethanols in water

The densities and heat capacities of the first four members of the 2-n-alkoxyethanols were measured in water over the whole mole fraction range with a flow densimeter and a flow microcalorimeter. The methoxy and n-propoxy homologs were studied at 25°C, ethoxyethanol at 19, 25, and 40C, andn-butoxyethanol at 4, 10, 25, 40, and 55°C. While methoxyethanol behaves as a fairly typical polar nonelectrolyte in water,n-butoxyethanol shows trends in the concentration dependence which resemble micellization; some pseudo-microphase transition occurs at about 0.02 mole fraction, and this transition concentration decreases with increasing temperature. There is no simple relationship between this phenomenon and the existence of a lower critical solution temperature at 49°C since the sharpness of the thermodynamic changes is maximum at the lowest temperature and at 55°C the apparent molal quantities on both sides of the two-phase region appear to fall on the same continuous curve. In the region prior to the pseudo-microphase separation the apparent and partial molal heat capacities decrease regularly but beyond approximately 0.01 mole fraction increase sharply to a maximum, suggesting some type of pre-association. The apparent molal heat capacity of water in the binary solutions is larger than the molar heat capacity of water over the whole mole fraction range. The present data seem to be consistent with a clathrate model for hydrophobic hydration and interactions with these systems.     

Volumetric properties of the binary mixture <Emphasis Type="Italic">n</Emphasis>-heptane+ethylbenzene mixtures at high temperatures and high pressures

New experimental data on the density of three (0.2393, 0.4856 and 0.7390 mole fraction of ethylbenzene) binary n-heptane+ethylbenzene mixtures have been measured with a constant-volume piezometer immersed in a precision liquid thermostat. These new experimental data covering a temperature range from 306 to 527 K and a pressure range of 0.1 to 11 MPa. The experimental data reported here have an uncertainty less than 0.06% for the density, 0.05% for the pressure, 15 mK for the temperature, and 0.012% for the concentration. Excess molar volumes were derived using measured values of density for the mixtures and for the pure components calculated with reference equation of state for n-heptane (Span and Wagner, 2003) and for the pure ethylbenzene (Frenkel et al., 2005). The derived values of excess molar volumes at atmospheric pressure were compared with the values reported by other authors in the literature. The effect of pressure on the excess molar volumes was studied.     

Thermodynamic properties of binary mixtures of 2-hexanone withn-alkanes at 35°C

Excess molar enthalpies h ^E and excess molar volumes v ^E of the binary liquid mixtures 2-hexanone+n-alkane (from n-heptane to n-decane) have been determined for various values of the mole fraction of hexanone at 35°C and atmospheric pressure. Excess molar enthalpies were determined by Calvet microcalorimetry and v ^E from densities measured by vibratingtube densimetry. The results are compared with the predictions of several group contribution models.     

Excess molar enthalpies and heat capacities of dimethyl sulfoxide + seven normal alkanols at 303.15 K and atmospheric pressure

Excess molar enthalpies and heat capacities of binary mixtures containing dimethyl sulfoxide (DMSO) + seven normal alkanols, namely methanol, ethanol, propan-1-ol, butan-1-ol, hexan-1-ol, octan-1-ol, and decan-1-ol, have been determined at 303.15 K and atmospheric pressure. With the exception of the DMSO-methanol system, which shows negative values, all mixtures show positive values of excess molar enthalpies over the whole range of mole fraction, increasing as the number of carbon atoms increases. Heat capacities of pure components have been determined in the range 288.15 < T (K) < 325.15. Molar heat capacities of the mixtures are always positive and decrease as the number of carbon atoms decreases. The results were fitted to the Redlich-Kister polynomial equation. Molecular interactions in the mixtures are interpreted on the basis of the results obtained.     

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VII. Thermodynamic of Interactions of Na+ Ion with 15-Crown-5 Ether in the Mixture of Water with N,N-Dimethylacetamide at 298.15 K

The thermodynamic functions of the complex formation of 15-crown-5 ether with sodium cation in mixtures of water with N,N-dimethylacetamide at 298.15K are calculated. The equilibrium constants of complex formation of 15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15K. The complexes are enthalpy-stabilized but entropy-destabilized in this mixed solvent. A quantitative dependence of the excess molar enthalpy and entropy of complex formation on the structural and energetic properties of interactions between water and organic solvent molecules in the mixtures of water with N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide has been found. The linear entropy–enthalpy relationship for complex formation is also presented. The solvation enthalpy of the complex in the water–N,N-dimethylacetamide mixtures is discussed.     

Synthesis and characterization of thermoresponsive poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-<Emphasis Type="Italic">N</Emphasis>-hydroxymethylacrylamide-co-2-hydroxyethyl methacrylate) hydrogels

Thermoresponsive hydrogels based on N-isopropylacrylamide, N-hydroxymethylacrylamide, and 2-hydroxyethyl methacrylate, poly(NIPAM–co-NHMAAm–co-HEMA), have been synthesized and their swelling—deswelling behavior studied as a function of NIPAM concentration, NIPAM/NHMAAm and NIPAM/HEMA mole ratio, and total monomer concentration. Copolymers varying in composition have been obtained by redox copolymerization of these three monomers. Temperature has been changed in the ranges from 4 to 70 °C at fixed pH and total ionic strength. Equilibrium swelling ratio, dynamic swelling ratio, and dynamic deswelling ratio were evaluated for all hydrogel systems. The equilibrium swelling ratios of the copolymeric gels decrease with increasing NHMAAm and HEMA content. The formation of the intermolecular hydrogen bonding between hydroxyl and amido groups decreases the hydrophilic group numbers of the gel and the affinity of the gel towards water decreases. The copolymer gels also showed rapid volume transitions with time. The time required for equilibrium shrinking increased with increasing NHMAAm and HEMA content in the gel.     

Conductance studies in amide-water mixtures. II. Sodium salts inN,N-dimethylformamide-water mixtures at 35°C

Conductance data for sodium nitrite, chloride, and acetate in water andN,N-dimethylformamide (DMF)-water mixtures (74.82D42.48) for the concentration range 0.001–0.04N, as well as the densities, viscosities, and dielectric constants of the solvent mixtures at 35°C, are reported. The data have been analyzed by the Fuoss (1975) equation. The existence of a maximum in the viscosity at a 13 mole ratio of DMF and water is indicated. The Walden products for all the three salts pass through a maximum while the equivalent conductances show a minimum with increasing DMF content. The maxima in the Walden product are attributed to the dehydration of ions by the cosolvent (DMF).Part I:Indian J. Chem. 14A, 1015 (1976).Deceased.     

Thermodynamic, transport, and spectroscopic studies for mixtures of isomeric butanediol and N-methyl-2-pyrrolidinone

The thermodynamic parameters viz. excess molar volume V^E and speed of sound u, transport parameter viscosity η, and spectroscopic parameters viz. IR, ¹H, ¹³C NMR have been measured for the mixtures of isomeric butanediol (1,2-, 1,3-, 1,4-, and 2,3-butanediol) and N-methyl-2-pyrrolidinone over the whole composition range at 308.15 K. The partial molar quantities , isentropic compressibility , viscosity deviation Δη, deviation in Gibbs free energies of activation for viscous flow g(x), and excess NMR chemical shift δ^E have been estimated and analyzed. Results show that the interaction between unlike molecules takes place through hydroxyl groups of isomeric butanediol and CO group of N-methyl-2-pyrrolidinone. Excellent agreement between thermodynamic and spectroscopic measurements is observed.     

Excess enthalpies of water+1,4-dioxane at 278.15, 298.15, 318.15 and 338.15 K

The excess molar enthalpies of (1–x)water+x1,4-dioxane have been measured at four different temperatures. All the mixtures showed negative enthalpies in the range of low mole fraction but positive ones in the range of high mole fraction of 1,4-dioxane. Excess enthalpies were increased with increasing temperature except those of at 278.15 K. Partial molar enthalpies have maximum around x=0.13 and minimum around x=0.75. Three different behaviors for the concentration dependence of partial molar enthalpies were observed for all temperature. Theoretical calculations of molecular interactions of three characteristic concentrations were carried out using the molecular orbital method.     

Excess thermodynamic properties of binary liquid mixtures containing cyclohexylamine at 30°C

The excess volumes of mixing of cyclohexylamine with n-hexane, n-heptene, n-octane, n-nonane, benzene, toluene, nitrobenzene, chlorobenzene and bromobenzene have been measured at 30°C. For all systems except for n-hexane, V ^E is positive over the entire mole fraction range. For the n-hexane mixtures, a sigmoid curve is obtained with negative V ^E at high mole fraction of amine.     

Partial Molar Volumes of Tetraalkylammonium Ions in N, N-Dimethylformamide

The densities of tetraalkylammonium bromide, R₄NBr (R = Et, Pr, Bu, Hex, Hep, Oct), solutions in dimethylformamide have been measured for the composition range (0.05–0.4) mol-kg⁻¹ at 25 ^∘C. Apparent molar V_φ and limiting partial molar volumes ⫫₂^o of the electrolytes have been evaluated. Using the extrapolation values, the limiting partial molar volumes of the tetraalkymammonium ions (⫫_i^o) have been calculated. Analysis of different contributions to the ionic ⫫_i^o indicated partial penetration of solvent molecules into the van der Waal’s volume of tetraalkylammonium (TAA) ions.     

Measurement of Some Thermodynamic and Acoustic Properties of Binary Solutions of N,N-Dimethylformamide with 1-Alkanols at 30°C and Comparison with Theories

Densities, and ultrasonic velocities, uof binary mixtures of N,N-dimethylformamide (DMF) + methanol, + ethanol, + 1-propanol, + 1-butanol, + 1-pentanol, and + 1-hexanol have been measured at 30°C. The ultrasonic velocities have been compared with values calculated from the free-length theory ( FLT) due to Jacobson and collision-factor theory ( CFT) due to Schaaffs. The measured data are used to compute adiabatic compressibility (k _s), deviation in adiabatic compressibility (k _s), intermolecular free length (L _f), molar volume (V _m), and available volume (V _a). The excess molar volume ( V _m ^E) and excess free length (L _f ^E) are also evaluated. For all systems, these results were satisfactorily correlated by the Redlich–Kister polynomial. These parameters are used to discuss dissociation of the self-associated 1-alkanol molecules and the formation of aggregates between unlike molecules through C=O...H–O hydrogen bonding.     

Coil-to-globule transitions of interfacial copolymers in better than theta-solvents

Experimental studies of the coil-to-globule transitions exhibited in better than -solvents by interfacial copolymers ofN-isopropylacrylamide and acrylamide imply that a lower bound for the value of n in then-clusters of poly(N-isopropylacrylamide) (PNIPAM) is 3. The corresponding upper bound is therefore likely to be 5 or 6. Statistical copolymers of PNIPAM containing upwards of 0.75 mole fraction of acrylamide (whose homopolymer does not itself displayn-clustering) exhibited this transition, which disappeared at higher mole fractions of acrylamide. Interfacial homopolymers ofN-ethylacrylamide and its statistical copolymers withN-isopropylacrylamide exhibitedn-clustering at all compositions.