Alcohol-water Binary Mixtures Research Articles

Structural transition in alcohol-water binary mixtures: A spectroscopic study

The strengthening of the hydrogen bonding (H-bond) network as well as transition from the tetrahedral-like water network to the zigzag chain structure of alcohol upon increasing the alcohol concentration in ethanol-water and tertiary butanol (TBA) — water mixtures have been studied by using both steady state and time resolved spectroscopy. Absorption and emission characteristics of coumarin 153 (C153), a widely used non-reactive solvation probe, have been monitored to investigate the structural transition in these binary mixtures. The effects of the hydrogen bond (H-bond) network with alcohol concentration are revealed by a minimum in the peak frequency of the absorption spectrum of C153 which occur at alcohol mole fraction ∼0·10 for water-ethanol and at ∼0·04 for water-TBA mixtures. These are the mole fractions around which several thermodynamic properties of these mixtures show anomalous change due to the enhancement of H-bonding network. While the strengthening of H-bond network is revealed by the absorption spectra, the emission characteristics show the typical non-ideal alcohol mole fraction dependence at all concentrations. The time resolved anisotropy decay of C153 has been found to be bi-exponential at all alcohol mole fractions. The sharp change in slopes of average rotational correlation time with alcohol mole fraction indicates the structural transition in the environment around the rotating solute. The changes in slopes occur at mole fraction ∼0·10 for TBA-water and at ∼0·2 for ethanol-water mixtures, which are believed to reflect alcohol mole fraction induced structural changes in these alcohol-water binary mixtures.

“Non-Evaporating” Microdroplets on Self-Assembled Monolayer Surfaces under Ambient Conditions

A unique "non-evaporation" phenomenon, i.e., the unusually slow evaporation process of sessile microdroplets on self-assembled monolayer (SAM) surfaces, is reported. It has been observed that only droplets containing a certain proportion of a volatile and a less-volatile component undergo non-evaporation, which is characterized by hours-long existence of the droplets maintaining constant contact angle, contact area, and volume. We propose that for alcohol-water binary mixtures on SAM surfaces, the highly orientated and closely packed hydrophobic 1-decanethiol molecules induce a concentration gradient of alcohol in water, with a higher concentration of alcohol near the SAM surface. Initial evaporation of the alcohol (more volatile) increased the contact angle until the establishment of a new composition, which contains a strong hydrogen-bonding network among the water molecules in the presence of the alcohol alkyl chains. There is a lessened tendency for the alcohol to evaporate in the presence of a concentration gradient due to such interactions, which results in the observed "non-evaporating" phenomenon. This type of unusual evaporating profile was not observed on conventional substrates, such as polycarbonate sheets and microscope glass slides modified with alkyltrichlorosilanes.

Ultrasonic velocity measurements in ethanol–water and methanol–water mixtures

In this study, ultrasonic velocity measurements were used to estimate the alcohol type and volume concentration in water–alcohol binary mixtures. Varying mixtures of ethanol in water and methanol in water were prepared and the ultrasonic velocities for each concentration level were measured between 10 and 50 °C. Results of the statistical analyses indicated that ultrasonic velocity measurements can be used to distinguish between ethanol and methanol in a water–alcohol binary mixture and to estimate the alcohol concentration level. The results were validated by testing three commercial liquids with a known ethanol concentrations and one commercial liquid with known methanol concentration.

Study of Kinetics of Bromophenol Blue Fading in Alcohol-Water Binary Mixtures by SESMORTAC Model

Solvent effects on the kinetics of bromophenol blue fading have been investigated within a temperature range in binary mixtures of methanol, ethanol, 1-propanol, ethylene glycol and 1,2-propanediol with water of varying solvent compositions up to 40% by weight of organic solvent component. Correlation of logk with reciprocal of the dielectric constant was linear. Finally a mechanism was proposed for the bromophenol blue fading upon SESMORTAC (study of effect of solvent mixture on the one-step reaction rates using the transition state theory and cage effect) model, by means of this model, the fundamental rate constants of the fading reaction in these solvent systems were calculated.

Phase separation of water–alcohol binary mixtures induced by the microheterogeneity

The relationship between liquid-liquid phase separation and microheterogeneity in water-primary alcohol mixtures was examined by analysing the mass spectra of clusters generated through the fragmentation of liquid droplets. By comparing the cluster structures of water-ethanol, -1-propanol, and -1-butanol binary mixtures at various alcohol concentrations, we discovered differences in the molecular clusters that control phase separation. We also studied the role of water in alcohol self-association. Alcohol self-association is promoted in the presence of a small amount of water (ca. 10 approximately 20 wt%), in which the water-water hydrogen-bonding network is weak and does not contribute to alcohol self-association. We have demonstrated that alcohol self-association is also promoted by non-ideal mixing with other alcohols. The self-association of alcohol molecules complements the loss of stabilization energy caused by the relatively weak coexisting interactions. This complementary relationship among intermolecular interactions is an inherent property of solutions, and plays a key role in the phase separation process.

The Landau–Placzek ratio of water–alcohol binary mixtures

Rayleigh–Brillouin scattering was performed for water and alcohol (methanol, ethanol, 1-propanol and 2-propanol) binary mixtures. The Landau–Placzek ratio depends on both concentrations and molecular weights, and qualitatively corresponds to the ultrasonic absorption. Microscopic concentration fluctuation mainly affects the Landau–Placzek ratio of water–alcohol mixtures.

Preferential Solvation Studied by the Fluorescence Spectrum of Pyrene in Water-Alcohol Binary Mixtures

Abstract The local mole fraction of an alcohol such as methanol, ethanol, and 1-propanol was determined on the basis of the polarity variation sensed by pyrene in water-alcohol binary mixtures. The data indicate that alcohol molecules preferentially solvate pyrene in water; the degree of preferential solvation increases with an increase in the extent of the hydrophobic interaction between pyrene and alcohols.

Solvation of inorganic complexes in octanol-water, hexanol-water, and related microemulsions

Solubilities of tris(ethylmaltolato)iron(III) have been determined in dry 1-octanol, 1-hexanol and isobutanol and in the limited ranges of alcohol-water binary mixtures accessible for these alcohols. The observed pattern is discussed in terms of particularly favourable synergic solvation in the mixed solvents and is compared with solvation patterns indicated by the solvatochromic iron(II) complex Fe(CN) 2(bipy) 2.

Membrane permeation of water—alcohol binary mixtures

The permeability and selectivity of nylon-6, cellophane, and cellulose 2.5-acetate membranes toward binary mixtures of aliphatic alcohols and water were studied at 60°C. Commercial membranes made of the above materials were used with and without preswelling. The cellophane membranes swelled considerably more than the other types of membranes in both water and in aqueous isopropanol mixtures containing over 40 mole% H 2O. Therefore, the effects of swelling on membrane permeability were examined in some detail with cellophane membranes. The permeability characteristics of cellophane membranes could be altered significantly by suitable pretreatment. The effects of pretreatment are negligible in the case of cellulose 2.5-acetate and nylon-6 membranes.

Distinguishing between outer-sphere and inner-sphere redox mechanism on the basis of the solvent effect

During kinetic studies of redox reactions of U3+ ions, we paid special attention to the influence of water-alcohol binary mixtures on the reaction rate. Kinetic data suggest that the water-tert-butanol system is of a high diagnostic value. The dependence of log kexp on the molar fraction of tert-butanol passes through a characteristic minimum in the case of an outer-sphere mechanism, whereas in the other case it decreases monotonously.

Kinetics of aquation of chloro- and thiocyanato-chromium(III) complexes in mixed aqueous solvents

Rate constants are reported for spontaneous thermal aquation of the complexes [Cr(NH3)5Cl]2+, cis-[Cr(en)2Cl2]+(en = ethylenediamine), trans-[Cr(OH2)4Cl2]+, and [Cr(NCS)6]3– in a range of solvents, including methanol–, ethanol–, acetone–, dioxan–, and t-butyl alcohol–water binary mixtures. These results, and previously published results on similar chromium (III) complexes, are discussed in terms of the Grunwald–Winstein treatment of solvolyses in mixed aqueous solvents. Although this empirical approach can usefully be employed in discussing the aquation of chlorochromium(III) complexes, its extension to thiocyanatochromium(III) complexes does not seem profitable.