Some structural peculiarities of CH3COOH-H2O binary mixtures according to proton spin-spin relaxation data

The proton spin-spin relaxation method was used to study the acetic acid-water binary system. The structure of the binary mixture is stabilized over the whole range of concentrations of acetic acid. For heterosolvates, the simplest composition has been determined.Original Russian Text Copyright © 2004 by V. Yu. Buzko, I. V. Sukhno, V. T. Panyushkin, and T. E. DzhioevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 751–754, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Some Structural Features of HCOOH-H2O Mixtures According to Proton Spin-Spin Relaxation Data

The structure of the formic acid-water system was studied by proton spin-spin relaxation at 298 K. The simplest compositions of the heterosolvates were determined.     

Dielectric relaxation studies of binary mixtures of N-methylacetamide and N-methylformamide in benzene solutions using microwave absorption data

Using standard microwave X-band technique and by following Gopala Krishna's single frequency (9.90?GHz) concentration variational method, the dielectric relaxation times (τ) and the dipole moments (μ) of dilute solution of N-methylacetamide (NMA), N-methylformamide (NMF) and NMA?+?NMF binary mixtures in benzene solutions have been calculated at different temperatures. The energy parameters for the dielectric relaxation process for NMA?+?NMF binary mixture containing 30?mol% NMF have been calculated at 25, 30, 35 and 40°C and compared with the corresponding viscosity parameters. A good agreement between the free energy of activation from these two sets of values shows that the dielectric relaxation process like the viscous flow process can be treated as the rate process. From relaxation time behavior of NMA and NMF binary mixture in benzene solution, solute–solute types of the molecular association has been proposed.     

A study of shear-stress relaxation anomalies in binary mixtures of monodisperse polystyrenes

We report measurements of the nonlinear relaxation moduli after a step-shear strain of polystyrene solutions with nearly monodisperse and with bidisperse distributions of molecular weight. We find, as have others, that for monodisperse solutions with M/M_e > 60, there are anomalies, such as an unusually low nonlinear modulus and a kink in a plot of shear stress versus time after the step strain. Here M is the polymer molecular weight and M_e is the entanglement molecular weight. We find that in the bidisperse solutions the anomalies persist as long as M_w/M_e > 60, where M_w is the weight-averaged molecular weight of the bidisperse solution. The persistence of the anomalies in bidisperse solutions disagrees with a theory of Marrucci and Grizzuti that attributes the anomalies to strain inhomogeneities similar to shear banding. The Marrucci-Grizzuti theory predicts that as little as 10% short chains in the bidisperse mix should eliminate the anomalies, whereas in the experiments reported here at least 30% is required. Nevertheless the way in which the anomalies disappear at high strains when one increases the fraction of low-molecular-weight component is qualitatively similar to the theoretical predictions and supports the notion that strain inhomogeneities occur in these systems. © 1992 John Wiley & Sons, Inc.     

Some structural aspects in binary aqueous mixtures of simple amides from rotational molecular motions

Nuclear magnetic relaxation rates of²D and¹⁴N in binary aqueous mixtures of formamide,N-methylformamide (NMF), andN,N-dimethylformamide (DMF) are reported as a function of the mixture composition. From these intramolecular quadrupolar relaxation data separate rotational correlation times for the two components of the mixture can be determined. The relative variation of the single correlation time as a function of the composition is interpreted in terms of structural changes caused by hydrogen bonding and hydrophobic effects. The results also clearly reflect the expected characteristic variation of these effects on the rotational molecular motions in going from formamide to NMF and DMF. The maximum correlation time retardation of DMF in the aqueous mixture is compared with those of other hydrophobic solvents. A correlation between this maximum retardation and the excess enthalpy of mixing of hydrophobic solvents in aqueous solution can be established graphically.     

Some comments on nature of the structural relaxation and glass transition

We report on an experiment and new formula revealing dynamic and structural heterogeneity observed in liquids and polymeric systems. The formula applied to data obtained by mechanical spectroscopy reveals the glass-forming system behaviour giving the parameters previously postulated. The presented results are compared with data obtained for liquids (oligomers) confined to nanoporous media. To explain the behaviour of the polymeric systems the three-phase model is considered.     

Dielectric relaxation of butyl acrylate—alcohol mixtures using time domain reflectometry

Dielectric relaxation measurements of butyl acrylate—alcohol mixtures at different concentrations and temperatures within the frequency range of 10 MHz to 10 GHz have been carried out using time domain reflectometry. Parameters such as the static permittivity, dielectric relaxation time, the Kirkwood correlation factor, the excess inverse relaxation time, and thermodynamic functions were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The value of the dielectric properties decreases with increasing butyl acrylate concentration in alcohol and systematically varies with the length of alcohol alkyl chain. Negative values of the excess inverse relaxation time found for all concentrations and at all temperatures studied may indicate that the effective dipoles rotate slowly.     

Microwave dielectric spectra and molecular relaxation in formamide-N,N-dimethylformamide binary mixtures

The dielectric dispersion and absorption spectra of formamide (FA), N,N-dimethylformamide (DMF) and their binary mixtures are investigated in the frequency range of 500 MHz to 20 GHz at 30 °C in view of the organic synthesis by microwaves heating using amides solvents. The concentration dependent values of molecular reorientation relaxation times lower than that of the ideal mixing behaviour have been attributed to the cooperative dynamics of H-bonded FA–DMF structures. The molar ratio of stable adduct is 2:1 of FA to the DMF, which is determined from the concentration dependent excess static dielectric constant and the relaxation time plots of these binary mixtures. Electrode polarization effect and ionic conduction in FA and DMF were investigated from their dielectric dispersion spectra in the low frequency region of 20 Hz to 1 MHz.     

Spin-lattice relaxation behaviour of water in cellulose materials in relation to the tablet forming ability of microcrystalline cellulose particles

Medical tablet forming ability of microcrystalline cellulose (MCC) was investigated in relation to the mobility of water molecules in MCC particles. For this purpose, the spin-lattice relaxation time T1 of water in the system was measured by 1H-NMR. Over a wide range of water contents (0.02 H2O/cellulose (g/g) 1.79), two different T1 (T1,l and T1,s) values were observed for water in each MCC sample. Below the equilibrium water content, water having these two different T1 values exchange with each other in an MCC particle reaching an equilibrium state within a given time scale (equilibrium constant K). The T1,l, T1,s and K values for water in MCC, estimated at the equilibrium water content, showed fairly good correlations with the hardness of the tablets made by the MCC samples. Sample with a shorter T1, or larger K tended to have a stronger tablet forming ability. In the spin-spin relaxation time T2 measurements for protons in an MCC/D2O system, two T2 components originating from the glassy cellulose solid (T2,G) and the swelling region (T2,l) were observed. It was found that the mole fraction xL of protons with T2,L in the system exhibits a clear linear correlation with K. From these results, a structural model for the distribution of water in MCC particles was propoed by taking the surface of each microfibril and the disordered region within the microfibril into consideration     

Application of continuous wavelet transformation to the simultaneous kinetic determination of binary mixtures

Wavelet transformation of kinetic profiles as a new and simple method was developed for the simultaneous determination of binary mixtures without prior separation steps. The mathematical explanation of the procedure is illustrated. Daubechies (db), symlet (sym) and discrete meyer wavelet (meyr) from the family of wavelet transforms were selected and applied under the optimal conditions for the resolution of binary mixtures. A model data as well as experimental data were tested. The results from the experimental data relating to the simultaneous spectrophotometric determination of phosphate and silicate based on the formation of phospho- and silico-molybdenum blue complexes in the presence of ascorbic acid, and also simultaneous determination of Co²⁺ and Ni²⁺ based on their complexation reactions with 1-(2-pyridylazo)-2-naphthol (PAN) in micellar media at pH 6.0 were presented as real models. The proposed method was validated by simultaneous determination of phosphate and silicate in detergent and tap water and also Co²⁺ and Ni²⁺ in tap water samples.     

Dielectric properties of binary mixtures of n-methylbenzenesulfonamide

The dielectric permittivities of binary mixtures of N-methylbenzenesul-fonamide (N-MBS) with benzyl alcohol, 1,2-dichloroethane, 1,4-dioxane and hexamethylphosphortriamide were measured as a function of mole fraction over the whole composition range at 30 and 50°C. The excess dielectric permittivities and the excess molar polarizations were also calculated. The excess dielectric permittivities ^E and excess molar polarizations P_E were found to be negative for N-methylbenzene-sulfonamide mixtures with benzyl alcohol and 1,4-dioxane, ^E values were positive and P^E values negative for mixtures with 1,2-dichloroethane, and ^E and P^E values were clearly positive for mixtures with hexamethylphosphortriamide. The results are discussed in terms of the strength of the dipolar and hydrogen-bonding interactions between the molecules in various binary mixtures.     

Phase behaviour of binary mixtures of colloidal charged spheres

As a step towards the modelling of binary metal alloys we here report on the shape of the phase boundary of two deionized charged sphere colloidal suspensions as a function of mixing ratio and particle density. Their size ratios are r = 0.68 and r = 0.56. Both aqueous suspensions of polystyrene copolymer spheres crystallize in a body-centred cubic structure. Interesting differences in the shape of the phase boundary are observed. In the first case a peaked increase of crystal stability was observed for a mixing ratio of p = 0.2–0.3, which gives the fraction of small spheres. Also in the second case the stability of the crystalline phase is larger than expected for an ideal solid solution but over a more extended range of small p. In addition at p = 0.7–0.8 we find a pronounced suppression of crystallization and furthermore some indications of a precipitation of one species at p = 0.9. While the first phase diagram resembles that of a solid solution with possibly the onset of compound formation, the second more resembles a eutectic.     

Correlation between topological features and surface tension of binary liquid mixtures

Summary The excess surface tension of a large number of binary liquid mixtures has been correlated with their topological features quantified in terms of the molecular connectivity indices. The agreement between the calculated and experimental ^E values is reasonably well for all the mixtures. A simple correlation has also been proposed between ^E and molar excess volume (V ^E ) of a binary mixture. The correlation is quite useful in correlating ^E data even for the mixtures where either one or both the components are associated in the pure state and/or there is interaction between them.

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Korrelation zwischen topologischen Gegebenheiten und Oberflächenspannung von binären flüssigen Mischungen

Zusammenfassung Die Exzeß-Oberflächenspannungen einer großen Anzahl von binären flüssigen Mischungen wurden mit der Topologie ihrer Komponenten in Form der molekularen Konnektivitätsindices korreliert. Die Übereinstimmung zwischen den ^E -Werten ist für alle Mischungen relativ gut. Es wurde ebenfalls eine einfache Korrelation zwischen ^E und den molaren Exzeß-Volumina (V ^E ) der binären Mischungen vorgeschlagen. Diese Korrelierung ist nützlich, um die ^E -Werte sogar dann für die Korrelation von Mischungen verwenden zu können, wenn entweder eine oder beide Komponenten im Reinzustand assoziiert sind und/oder eine Wechselwirkung zwischen ihnen besteht.

     

Complex formation of Al2(SO4)3 in water-formamide mixtures

The kinetics of formation of AlSO ₄ ⁺ has been investigated in mixtures of water and formamide. In contrast to similar measurements with BeSO₄, the substitution of solvating formamide molecules by the sulfate ion cannot be observed on the aluminum cation. On the other hand, with Al³⁺ cations three well separated water substitution processes are observed, as compared to a single one only with Be²⁺. An explanation for this behavior and for the different pH dependence of the sulfate complex formation for Al³⁺ and Be²⁺ cations is suggested.     

Phase behaviour of star-shaped binary mixtures of triphenylbenzenes,triphenylboroxines and triphenyltriazines

ABSTRACT

Star-shaped nonaalkoxy-1,3,5-triphenyltriazines were prepared and their mesomorphism was investigated by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (WAXS and SAXS). Compounds with chain lengths C₉ – C₁₂ displayed enantiotropic hexagonal columnar mesophases over a wide range of temperature. Their similarity in molecular size and mesomorphism prompted us to study their binary mixtures with previously reported planar 1,3,5-triphenylboroxines and propeller-shaped 1,3,5-triphenylbenzenes. All three compounds are fully miscible in their hexagonal columnar mesophases, but mixtures of planar with propeller-shaped compounds generated columnar stacks that contain only one type of molecule to avoid their shape incompatibility. However, the two types of columnar stacks were fully miscible which circumvented macroscopic phase separation.     

On the effect of temperature on the dielectric relaxation time of some benzene derivatives and certain of their binary mixtures

Dielectric relaxation behaviour of polar molecules in a non-polar solvent, or mixtures of these substances at different microwave frequencies and over a range of temperatures and concentrations give an idea about inter- and intra-molecular forces. Also such studies enable one to calculate thermodynamic parameters such as, the change of activation energy for dipole orientation (Δ G?), the enthalpy (Δ H?) and entropy (Δ S?) of activation. Such studies in the case of binary, ternary, etc. mixtures of polar molecules in pure liquid phase or in dilute solution phase of them in a non-polar solvent help in drawing certain quantitative conclusions regarding their relaxation behaviour as to whether a single component is responsible for observed microwave absorption, or a cooperative phenomenon (average) by all the dipoles of the mixture contribute to it. An experimental investigation is here performed on typical systems. With this in view, systematic dielectric measurements in a range of temperatures are carried out at a single microwave frequency on a single weight fraction in benzene of the four substituted phenols, namely, p-fluorophenylacetonitrile, p-bromonitrobenzene, m-bromonitrobenzene and 2-chloro-6-fluoro-benzaldehyde and on binary (1?:?1) mixtures of [p-2-chloro-6-fluoro-benzaldehyde?+?o-ethylphenol] and [p-fluorophenylacetonitrile?+?2-n-butyl phenol] in benzene as solvent at different temperatures. The results are presented and discussed.     

Parallel factor analysis of HPLC-DAD data for binary mixtures of lidocaine and prilocaine with different levels of chromatographic separation

A set of 17 samples containing a constant amount of lidocaine (667 μM) and a decreasing amount of prilocaine (667-0.3 μM) was analysed by LC-DAD at three different levels of separation, followed by parallel factor analysis (PARAFAC) of the data obtained. In Case 1 no column was connected, the chromatographic resolution (R_s) therefore being zero, while Cases 2 and 3 had partly separated peaks (R_s=0.7 and 1.0). The results showed that in Case 1, analysed without any separation, the PARAFAC decomposition with a model consisting of two components gave a good estimate of the spectral and concentration profiles of the two compounds. In Cases 2 and 3, the use of PARAFAC models with two components resolved the underlying chromatographic, spectral and concentration profiles. The loadings related to the concentration profile of prilocaine were used for regression and prediction of the prilocaine content. The results showed that prediction of prilocaine content was possible with satisfactory prediction (RMSEP<0.01). This study shows that PARAFAC is a powerful technique for resolving partly separated peaks into their pure chromatographic, spectral and concentration profiles, even with completely overlapping spectra and the absence or very low levels of separation.     

A correlation of gas solubilities and kinetics of hydrolysis in binary aqueous mixtures

A treatment which predicts the solubilities of gases in solvent mixtures is examined in the context of the analysis of kinetic data for reactions in aqueous mixtures. The treatment is qualitatively successful to some extent in resolving the effects of changes in the initial state of the reacting substrate in the activation parameters.