Dilute Aqueous Solutions Of Alcohols Research Articles

Relaxation and equilibrium properties of dilute aqueous solutions of alcohols

Regularities of equilibrium state establishment in dilute aqueous solutions of alcohols and the concentration and temperature dependences of the contraction, which is one of the simplest and important thermodynamic characteristics of solutions, were considered. The equilibrium state in aqueous solutions of the alcohols is established for days and even weeks after preparation. Such a slow relaxation process is directly related to the formation of the microheterogeneous state of the system and peculiarities of its time evolution. The character of the temperature and concentration dependences of the contraction is satisfactorily explained on the basis of the simplest virial equation of state assuming that its parameters are determined by the averaged potentials of intermolecular interaction. The physical nature of peculiar points of aqueous solutions of alcohols, i.e., intersection points of the contraction curves or points in the vicinity of which the intensity of molecular light scattering anomalously increases, was considered. The appearance of peculiar points depends on orientational correlations in water. The possibility of existence of peculiar points in other binary solutions is also discussed.

Aqueous solutions of lower alcohols investigated by pyrene fluorescence spectroscopy

The aqueous solutions of lower alcohols such as methanol, ethanol, 1-propanol and 2-propanol, were studied by fluorescence spectroscopy of pyrene, defining the Py scale for polarity. Sigmoidal curves were used to fit the Py values of aqueous alcohol solutions as a function of the logarithm of water–alcohol mole ratio, i.e., log(WAR). The results from curve fittings were discussed in terms of the structural transitions of aqueous alcohol solutions, as well as the dissociation constants for alcohol– and water–pyrene complexes. The microscopic alcohol and water phases were considered to be saturated with each other, and the structures of dilute aqueous alcohol solutions were found to be more complicated than those of concentrated ones.

Observation of Marangoni flow in ordinary and self-rewetting fluids using optical diagnostic systems

Dilute aqueous solutions of alcohols with a high number of carbon atoms can be considered as self-rewetting fluids due to their properties associated to an anomalous dependency of the surface tension with temperature in some ranges of concentrations. In this paper research activities focused on numerical simulations and laboratory experiments of the behaviour of a thin layer of liquid subject to a horizontal thermal gradient. The investigated liquids include ordinary liquids and water/alcohols mixtures. Physical properties measurements, in particular surface tension and refractive index, are also presented. Flow visualization and interferometric analysis have been carried out using optical diagnostic systems.

3P-001 希薄アルコール水溶液中の球状タンパク質の体積挙動(蛋白質・物性(3),第46回日本生物物理学会年会)

3P-001 希薄アルコール水溶液中の球状タンパク質の体積挙動(蛋白質・物性(3),第46回日本生物物理学会年会)

Technical Note: The Stability of Aqueous Alcohol Standard used in Breath Alcohol Testing after Twenty-Six Years Storage

ABSTRACTThe long-term stability of dilute alcohol aqueous solutions used in breath alcohol testing was determined after approximately twenty-six years storage at room temperature. At each alcohol concentration, aliquots from four single-sealed polyethylene bottles containing 500 mL of solution at manufactured alcohol concentrations of 0.484, 2.420, 3.025, and 3.630 mg/mL, were analysed in triplicate by headspace gas chromatography. After twenty-six years storage, the mean percent changes (and ranges) were +4.4 (−6.5 to +8.3), +0.6 (−13.9 to +5.5), −2.0 (−15.6 to +3.5) and −26.3 (−39.1 to +3.9) for each concentration, respectively. The greatest percent loss in alcohol occurred in the alcohol standard at the highest concentration and decreased at the lower alcohol concentrations tested. Dilute aqueous alcohol solutions (of 3.035 mg/mL or less) show remarkable stability after long term storage at ambient temperatures.

Hydrophobic self-assembling in dilute aqueous solutions of alcohols and hydrocarbons

Microheterogeneities, such as local compositions which differ from the average ones, are typical features of aqueous solutions of organic substances. A method for computing the sizes of microheterogeneities at infinite dilution (correlation volumes) is proposed, which is based on a combination between the Kirkwood–Buff theory of solution, an expression for the local concentration, ab initio quantum chemical calculations of the interaction energies and available thermodynamic data. The correlation volumes are calculated for aqueous solutions of methanol, ethanol, propanol and isopropanol. The results obtained for propanol and isopropanol could be compared with the sizes determined via small-angle X-ray scattering and good agreement between the calculated and experimental values found. In addition, the mutual affinity of solute molecules (their self-assembling), which is one of the important characteristics of hydrophobic interactions in aqueous solutions, was evaluated for a number of infinitely dilute aqueous solutions of alcohols and hydrocarbons. The calculations provided an additional argument that the hydrophobic self-assembling of hydrocarbons is mainly a result of the preference of the water molecules to interact among themselves via hydrogen bonding than a result of the interactions between hydrocarbon molecules.

Difference spatial distribution function analysis of aqueous solutions. III. Hydration structures of alcohol and ether solutions having straight chain and branched alkyl groups.

Spatial distribution functions (SDFs), gOO(x,y,z) and gOH(x,y,z), obtained from Monte Carlo simulations at 298 K were applied to characterize the anisotropic structure of infinitely dilute aqueous solutions of alcohols and ethers having straight chain and branched alkyl groups. In spite of the different size and shape of the hydrophobic groups, the spatial orientation of the hydrogen-bonded water molecules was found to be of linear type with a triple layer structure in the hydrogen acceptor (HA) region and a double layer structure in the hydrogen donor (HD) region. The volumes and the coordination number (CN) in the HA region were essentially identical for all alcohol and ether solutions, but the volumes for the isopropyl alcohol (IPA) and isopropyl methyl ether (IPE) solutions were greater than those for the other solutions. In the hydrophobic hydration (HH) region, these values increased with increasing size and shape of hydrophobic groups, except in the case of IPA and IPE solutions. These results indicated that the hydration structures around the isopropyl group in alcohol and ether solutions differed from those in other solutions. From the results of the difference SDF (DSDF), AgOO(x,y,z), between SDFs gOO(x,y,z) for the two states, it was apparent that the distribution of hydration water molecules in the HA region for ether solution was characterized by the increase of the distribution in the direction of lone pair electrons on the oxygen atom of the solute molecule with increasing hydrophobicity.

Diffusion and Structure in Dilute Aqueous Alcohol Solutions: Evidence for the Effects of Large Apolar Solutes on Water

By measuring the dependence of molecular motion on pressure, p, using diffusion measurements as a probe, one can obtain information regarding the structure of solutions containing amphiphilic solutes having apolar or hydrophobic groups. We have found that at low temperatures, the intra-diffusion coefficient (D) of water in a dilute solution of aqueous tert-butyl alcohol (mole fraction, x = 0.025) shows a maximum with increasing p, to a greater relative extent than in pure water under the same conditions. This suggests the water in these solutions is more “structured” than in pure water, though there is a clear distinction from the effects produced by large “structure breaking” ions as solutes where the absolute water diffusion coefficient may show a maximum as concentration or pressure is increased. We have made a survey of a number of other water−alcohol systems; a similar large enhancement occurs in 2-propanol solutions. In solutions of methanol, ethanol, and 2,2,2-trifluoroethanol, the enhancement is similar to that of water with no additional effect. Volumes of activation (ΔVD) have been calculated from the diffusion data. From an analysis of the T and p dependence of D and ΔVD, we have concluded that the mechanism for the diffusion of water in these solutions seems likely to be the same as for pure water. The molecules can move around the obstacle solute molecules via the labile hydrogen-bonded network. Where the temperature is low and the solute alcohol molecules are large, the network appears to be distorted such that the effect of pressure on water diffusion is greater with the maximum appearing at higher pressures than in pure water.

Dilute single and mixed solute systems in a spiral wound reverse osmosis module: Part II. Experimental data and application of the model

In Part I of this paper a system design model for a spiral wound reverse osmosis module was developed. The model allows for the choice of membrane mass transport model and describes material balances, pressure drop, and mixing in the feed channel. In the current paper this model is used to analyze data for single and mixed solute experiments with dilute aqueous alcohol solutions. A commercial FilmTec FT-30 brackish water spiral wound membrane module was used in all experiments. The unknown parameters in the model determined from single solute experimental data can be used to predict the performance for multiple solute experiments. The model predictions for both single and multiple solute separations are consistent with the experimental results over a wide range of pressures and feed flow rates. The mesh step model was shown to describe the mixing in the feed channel spacer well. A further result is the solute transport parameters from the Kimura Sourirajan Analysis were found to be correlated to the steric or polar Taft parameters for this membrane module.

Volumetric Properties of Dilute Aqueous Alcohol Solutions at Different Temperatures

Abstract The densities of dilute aqueous solutions of normal alcohols (from methanol to 1-hexanol) and branched-chain alcohols (2-butanol, 2-methyl-1-propanol, and 2,2-dimethyl-1-propanol) were measured at 5, 15, 25, 35, and 45 °C by means of an oscillating-tube densimeter. The apparent molar volumes of the alcohols in aqueous solutions were determined. The temperature dependences of the limiting partial molar volume, excess partial molar volume, concentration dependence, and methylene group contribution to volume were discussed. An alternative analysis based on the use of specific units instead of molar units was also attempted. The characteristic volumetric behavior of aqueous alcohol solutions is more pronounced for shorter- or branched-chain alcohols rather than hydrophobic alcohols. There is no definitive evidence that so-called hydrophobic hydration around the alkyl groups of alcohol in water is accompanied by a prominent volume change. The unique properties, such as negative partial molar expansion, may originate from the hydrogen-bonding interactions between water and alcohol OH groups.

Infrared and X-ray photoelectron spectroscopy of aminophenyltrimethoxysilane films on metals

The molecular structures of thin films formed by aminophenyltrimethoxysilane (APTMS) deposited onto mechanically polished aluminum, iron, and copper substrates from dilute aqueous alcohol solutions were determined using reflection-absorption infrared spectroscopy (RAIR) and X-ray photoelectron spectroscopy (XPS). The as-deposited films on all three substrates were similar and consisted of hydrolyzed oligomers that condensed to form siloxane polymers during heating at elevated temperatures. APTMS films on all three substrates reacted readily with epoxy resins at 150°C. Although some loss of nitrogen was observed, the films formed on aluminum were relatively stable during heating at 250°C and inhibited oxidation of the substrate. The films formed on iron and copper depolymerized rapidly during heating at 250°C and failed to inhibit oxidation of the substrates. It was concluded that APTMS films were potentially useful primers for use at high temperatures on aluminum, but not on copper or iron.

Effect of addition of alcohols on gas holdup and backmixing in bubble columns

AbstractGas holdup and axial dispersion coefficient data for dilute aqueous alcohol solutions and two different diameter columns at larger gas and liquid velocities compared to those of Schügerl et al. (1977) are presented. Data for cocurrent and batch systems are qualitatively explained using Zuber and Findlay's theory (1965) and bubble structure, and quantified further using a dynamic gas disengagement technique. Unified empirical correlations for the gas holdup and axial dispersion coefficients are presented.

Drag coefficient of relatively contaminated gas bubbles

AbstractBased on the velocity profiles around clean and relatively contaminated gas bubbles, the tangential and normal stress, pressure distribution at the surface around the gas bubbles, and finally the viscous, form and total drag coefficient of the gas bubbles were calculated and compared with experimental values for dilute aqueous solutions of alcohols. The theory verifies the experimental observation that the total drag coefficient of single gas bubbbles increases with the contamination factor. The effect of the void fraction of the gas bubble swarm on the total drag coefficient was examined by the use of a void function. Most of the void functions for the relatively contaminated gas bubble swarms were between the values of potential flow and that of solid spheres.

Maximum density effects in dilute aqueous solutions of alcohols and amines

The effect of dipropylamines and dibutylamines on the temperature of the maximum density of water has been determined as a function of amine concentration. These effects have been related to the temperature coefficient of the volume of mixing which for aqueous solutions of both amines and alcohols is negative, giving rise to a positive contribution towards the shift of the temperature of maximum density. This effect is attributed to the stabilization by the solute of residual long-range order present in liquid water, and a comparison is made with the clathrate hydrate structures.

Applications of infrared spectroscopy : The determination of small amounts of alcohols in aqueous solution

Recent developments in methods of analysing dilute solutions of alcohols are briefly reviewed, and a simple modification to the Zeisel reaction is described. This permits the analysis, on a 1 -ml aliquot, of dilute aqueous solutions of alcohols alone or in admixture.