Alcohol-water Mixtures Research Articles

The C-O Stretching Infrared Band as a Probe of Hydrogen Bonding in Ethanol–Water and Methanol–Water Mixtures

ABSTRACT Infrared spectra of the ethanol–water and methanol–water mixtures in the mole fraction range of 0.1 to 0.9 were recorded in the attenuated reflection (ATR) mode. Traditionally, the hydrogen bonding of water with other molecules has been studied by investigation of the OH stretching band frequencies and intensities of water. However, in the case of alcohol–water mixtures, this procedure presents a problem due to the complete overlap of the hydroxyl absorptions from the alcohol and water. In the present study, we have adopted an alternative approach of understanding the ethanol–water and methanol–water hydrogen bonds through the analysis of the C-O stretching band. The intrinsic high intensity of the C-O band and nearly complete absence of its overlap with the water bands make it a good candidate for the study of hydrogen bonding interactions in alcohol–water mixtures. The integrated areas of the C-O stretching band versus mole fractions were plotted for both mixtures. In the case of methanol–water mixtures, the C-O stretching band area plot was linear, whereas such plot for the ethanol–water mixtures had two distinct slopes that switched at the 0.5 mole fraction. The C-O band plot areas were used to explain the molecular associations in the mixtures studied.

Separation of isopropyl alcohol–water mixtures by pervaporation using copolymer membrane: Analysis of sorption and permeation

Membrane made from copolymer of acrylonitrile and methyl acrylate designated as PANMA was used for pervaporative dehydration of isopropyl alcohol (IPA) over the concentration range of 75–100wt% IPA in water. Sorption of the membrane was evaluated in terms of thermodynamic interaction parameters based on Flory–Huggins lattice model. Engaged species induced clustering (ENSIC) model was also used to explain swelling of the membranes. Coupling in sorption was explained by activity coefficient of water and IPA in feed and membrane using Flory–Hugging thermodynamics and also by interpolating ENSIC parameters. Intrinsic membrane properties like partial permeability and membrane selectivity was also determined. Total solvent volume fraction (TSVF) model was used to determine diffusion coefficient and plasticization coefficient of the solvents. The membrane was found to show very high water selectivity (3540) and good flux (3.3kg/m2hμm) for highly concentrated (99.8wt%) IPA at 30°C temperature.

Effect of alcohol and alcohol/water mixtures on crystalline structure of CdS nanoparticles

A simple approach is discussed to synthesise CdS nanoparticles using various pure alcohols and their mixtures with water as a reaction medium. The study highlights that the solvent plays an effective role not only in controlling the particle size but also the structure. The size and phase of CdS nanoparticles were controlled by thermal reaction between cadmium precursor and thiourea in alcohol and their mixtures with water. Use of pure alcohols for the synthesis produces cubic structure as revealed from X-ray diffraction (XRD), while mixture of water with alcohol gives rise to hexagonal phase. XRD showed the presence of CdS nanoparticles with size 10–13 nm in an alcohol–water mixture whereas use of alcohols alone showed size in the range 1–3 nm. The composition and structural features were also studied by Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Thiourea, in the presence of pure alcohol seems to be responsible for reduction in particle size as compared to that in the presence of alcohol/water mixture. The possible mechanism for the structural phase transition is discussed on the basis of change in surface energy and solvent–solvent interaction.

Stability of spray combustion for water/alcohols mixtures in oxygen-enriched air

The feasibility of burning fuels that are heavily diluted with water was evaluated. This concept could potentially be utilized to directly generate steam for a variety of applications, including power generation and enhanced oil recovery. Two water-soluble fuels, ethanol and 1-propanol, were heavily diluted with water and sprayed into a swirl-stabilized burner and the blow-off limits were obtained to identify the flame stability. The blow-off limit was experimentally determined as the lowest O2 concentration where a flame could exist under a given oxidizer flow rate. For the present experimental system, stability maps were determined as a function of fuel concentration and oxidizer flow rate for different types of nozzles and both alcohols. Contours of temperature and overall fuel mass fraction in the droplets were obtained for a flame burning 15wt% ethanol in an oxidizer of 50% O2 and 50% N2. The results revealed that preferential vaporization of ethanol over water plays an important role in enhancing flame stability. To further understand this, a model of bi-component droplet vaporization was employed for both the diffusion limit and distillation limit modes of liquid mass transfer. The results confirmed the preferential vaporization of ethanol and demonstrated that it is necessary to account for the non-ideal solution behavior of the alcohol–water mixture to appropriately model the vaporization process. The model also demonstrated that for this experimental system, droplet vaporization was better characterized by the distillation limit mode with enhanced mass transfer by convection.

A Radio Frequency Sensor For Measurement Of Small Dielectric Property Changes

We propose a sensitive radio frequency (RF) sensor for the measurement of small dielectric property changes. Interference is used to cancel parasitic background signals to improve sensitivity. The device consists of two Wilkinson power dividers, a 180 degree reversephase and an in-phase CPW (coplanar waveguide)-slotline back-toback balun. The small dielectric property changes between de-ionize water and two sets of primary alcohol-water mixtures with different concentrations in terms of molar fractions are measured with clear sensing and identification. The sensor offers almost thirteen times greater sensitivity than conventional transmission lines. Experimental results also show that the lowest detection limit for the molarity of primary alcohol is about 0.25% across the sensitive sensor. Compared with microwave soil moisture sensors the proposed RF device is more sensitive.

27Al and 31P NMR Investigations of Soluble Aluminophosphate Species in Alcohol–Water Mixtures

In this work, phosphorus-31 and aluminum-27 nuclear magnetic resonance techniques were used to characterize the distribution of soluble aluminophosphate species in methanol + water and ethanol + water mixtures. The assignment of the peaks to aluminate species was attempted, clarifying earlier work and producing information on the different aluminophosphate complexes. Nine peaks were observed at −0.41, −6.4, −7.5, −7.9, −13.1, −13.9, −16.6, −18.1 and −20.6 ppm. Four new peaks appeared in the 31P NMR spectra of the alcoholic aluminophosphate solutions and their intensities changed with changes of the alcohol:water volume ratio. These new peaks were observed in the presence of methanol or ethanol but not in aqueous solutions.

Effects of pH on Properties of Soy Protein Isolate/Guar Gum Composite Films

The objective of this research was to investigate the effect of pH(7.0, 8.0, 9.0, 10.0) on the properties of soy protein isolate (SPI)/guar gum (GG)composite films casted with 0.2 %(w/v)guar gum polysaccharide, 5.0 %(w/v)SPI, 1.5 %(w/v)glycerol plasticizer, and 4:1(v/v) mixture of distilled water and anhydrous alcohol. Composite membranes from different pH conditions were evaluated from following aspects: tensile strength (TS), elongation at break (EB), water vapor permeability (WVP), water solubility (WS) and surface hydrophobicity(SH)

Association in solutions of monoatomic alcohols and their mixtures with water

The association of certain monoatomic aliphatic alcohols in tetrachloromethane and in wateralcohol mixtures was studied by spectroscopy (from 800 to 1100 nm), the self-modelling curve resolution (using the MILCA algorithm), and quantum chemistry. The decomposition of spectral curves was used to determine the number, composition, and stability of associates over a wide range of concentrations (from 0 to 100 wt %). The ranges of concentration were determined for the existence of homo- and heteromolecular associates of alcohols. Our conclusions based on chemometric method were confirmed by quantum chemical simulations of the particles that can exist in a solution, and the data on the structure of associates of monoatomic alcohols were supplemented.

Thermochemistry of solvation and complexation in the Cu(NO3)2-water-ethanol-L-α-alanine system at 298.15 K

The heats of mixing of aqueous solutions of copper(II) nitrate and sodium alaninate and the heats of dilution of an aqueous solution of sodium alaninate in water-ethanol mixtures were calorimetrically measured at 298.15 K. The enthalpies of transfer of α-alaninate from water into water-alcohol mixtures and the standard molar enthalpies of the reaction of copper(II) complexation with α-alaninate ion in the mixtures under study are calculated. The resulting enthalpy parameters are compared with those of the similar system containing synthetic β-alanine, which was studied earlier.

Synthesis and properties of the composite ceramics from nanocrystalline Al2O3-30% Y0.1Zr0.9O2 prepared from a water-alcohol solution

The hydrogel of the mixed oxide Al2O3-30% Y0.1Zr0.9O2 was prepared by precipitation of ammonia from a water-alcohol mixture (1 : 5). The Al2O3-30% Y0.1Zr0.9O2 compound thus synthesized was characterized using differential scanning calorimetry, transmission electron microscopy, and the BET adsorption method. The obtained sample consisted of spherical particles with an average size of 16–20 nm and a specific surface area of 167 m2/g. The Al2O3-30% Y0.1Zr0.9O2 powder was pressed at 300 MPa and then calcinated at 1600°C for 2 h in air. The topographic and structural features of the prepared ceramics were determined using atomic force microscopy and X-ray electron probe microanalysis. The porosity, the Vickers microhardness, and the tensile strength were determined by mercury porometry.

Improvement of the Composition of Tunisian Myrtle Berries (Myrtus communis L.) Alcohol Extracts

Different extracts from myrtle berries were obtained using alcohol-water mixtures as an extraction medium in the range of 60-90% (v/v) to study the extraction efficiency in the preparation of myrtle liqueur. Flavonoids and anthocyanins were identified by high-performance liquid chromatography (HPLC) coupled with electrospray mass spectrometry and quantified during the maceration period by HPLC coupled with ultraviolet/visible detection. The antioxidant activity was tested by the 2,2-diphenyl-1-picrylhydrazyl assay. Dry matter, pH, and color parameters (L, a, b) were also analyzed. At the end of the maceration period, EE80 showed better anthocyanins stability and the highest total antioxidant activity (87.5%). These results suggest that the use of ethanol 80% provides the extract with the best characteristics for liqueur preparation. The present study contributes significantly to increase the marketing appeal of myrtle berries.

Aggregation induced emission switching and electrical properties of chain length dependent π-gels derived from phenylenedivinylene bis-pyridinium salts in alcohol–water mixtures

Supramolecular π-gels were formed in a mixture of aliphatic alcohols and water for a series of chromophoric phenylenedivinylene bis-N-alkyl pyridinium salts (PPV) appended with terminal aliphatic hydrocarbon chains of different lengths. Gelation could be controlled either by altering the ratio of various alcohol–water mixtures or by changing the aliphatic chain length of the gelator. The temperature- and the ratio-variation in the ethanol–water mixtures exhibited a tunable emission behavior depending on the extent of aggregation which was promoted by aromatic π-stacking, van der Waals and electrostatic interactions among the individual PPV units. Thus, a light-blue emission at higher temperature (>40 °C), a reddish-orange emission at low temperature (<20 °C) and a white-light emission at room temperature (25–30 °C) were observed in solution. The gelators possessing longer aliphatic chains exhibited a higher gel-melting temperature, increased viscoelasticity and shorter fiber diameter based on a delicate hydrophobic/hydrophilic balance. A semiconducting nature of the electrical conductivity was observed for the individual compounds and the magnitude of the current increased with increasing width of the gel fibers upon decreasing the aliphatic chain length. A reversible one-electron redox behavior was observed for the chromophore and the redox potential decreased with the increase in the chain length. A diffusion-controlled redox behavior was observed for the gelators with shorter aliphatic chains. However, the compounds with longer chains made the process diffusion-limited.

Aragonite growth in water-alcohol mixtures: Classical or nonclassical crystallization?

ABSTRACTAragonite can grow from calcium carbonate solutions as the favored phase, at ambient conditions, in the presence of 1:1 volume % water:ethanol. Its form is single and branched needles, with pseudohexagonal symmetry. Morphological evidence demonstrates that all precipitated aragonite is twinned. The recently popularized hypothesis of nonclassical growth by nanocrystal self assembly cannot describe the aragonite crystal form. Rather, its formation is effectively described as spherulitic growth, i.e. by classical crystal growth theory.

Crystallization of CaCO3in Water–Alcohol Mixtures: Spherulitic Growth, Polymorph Stabilization, and Morphology Change

The presence of alcohol in binary alcohol–water mixtures can affect the precipitation pathways of anhydrous crystalline CaCO3 polymorphs and their morphology. We explored the formation pathways and the effects of several parameters on calcite, vaterite, and aragonite: concentration of simple alcohols, time, and shaking speed, and we derived a multiparameter model for predicting what phase is preferred. We found that shaking speed and alcohol concentration are the most important parameters for affecting the stability of vaterite and aragonite and for changing vaterite morphology, from cauliflower-shaped, spherical aggregates, to dendritic, flatter structures. In all our experiments, the precipitated aragonite was twinned, and both the vaterite and aragonite can be interpreted to form through spherulitic growth. Classical growth theory fully describes their formation; there is no need to invoke the popular hypothesis for nonclassical growth by self-assembly of nanocrystals. These studies, and future work with solutions of low water activity, are paving the way to a better understanding of how organisms select their preferred polymorph and engineer CaCO3 morphology during biomineralization.

Structure and properties of porous film materials based on an aliphatic copolyamide

Phase segregation of solutions of ɛ-caprolactam-polyhexamethyleneadipamide copolymer in alcoholwater mixtures and the influence exerted on the pore structure and properties of film materials by the solution concentration and time of its keeping prior to deposition were studied.

A sample holder for soft x-ray absorption spectroscopy of liquids in transmission mode

A novel sample holder for soft x-ray absorption spectroscopy of liquids in transmission mode based on sample cells with x-ray transparent silicon nitride membranes is introduced. The sample holder allows for a reliable preparation of ultrathin liquid films with an adjustable thickness in the nm-μm range. This enables measurements of high quality x-ray absorption spectra of liquids in transmission mode, as will be shown for the example of liquid H(2)O, aqueous solutions of 3d-transition metal ions and alcohol-water mixtures. The fine structure of the x-ray absorption spectra is not affected by the sample thickness. No effects of the silicon nitride membranes were observed in the spectra. It is shown how an inhomogeneous thickness of the sample affects the spectra and how this can be avoided.

Novel Fluoropolymer Blends for the Fabrication of Sprayable Multifunctional Superhydrophobic Nanostructured Composites

We report a highly efficient technique to form novel fluoropolymer blend dispersions containing poly(vinylidene fluoride) (PVDF) and a fluorinated acrylic copolymer using a cosolvent system comprising N-methyl-2-pyrrolidone (NMP), acetone, and water under pH control. We also show that certain surface-functionalized, high-aspect-ratio nanostructured materials, such as organoclay and carbon nanowhiskers (CNWs), can be easily dispersed in these fluoropolymer blends to fabricate durable and functional superhydrophobic composite coatings upon spray casting. Both clay and CNW superhydrophobic coatings also repel lower surface tension liquids, such as water–alcohol mixtures (∼40 mN/m). Repellency is characterized using droplet sessile contact angle and contact angle hysteresis. Both clay and CNW-based composite coatings display self-cleaning properties (low contact angle hysteresis) for both water and water–alcohol mixtures. Additionally, electrical conductivity measurement of CNW composite coatings demonstrates...

Conformational Changes of Trialanine Induced by Direct Interactions between Alanine Residues and Alcohols in Binary Mixtures of Water with Glycerol and Ethanol

Despite the increasing relevance of characterizing local conformational distributions in the unfolded state, an unambiguous description of the role that solvation and the addition of certain cosolvents play in altering this ensemble has yet to emerge. Alcohol cosolvents, and specifically glycerol, are known to act as protein stabilizers. The underlying mechanism of this effect is, however, still debated. Short alanine-based peptides provide a suitable model system for exploring the influence of cosolvents on backbone conformations, as ample experimental evidence now indicates that alanine does not exhibit a true statistical coil behavior but rather shows strong preference for sampling the polyproline II (PPII) region of the Ramachadran map when solvated in water. To explore the effect glycerol and ethanol cosolvents have on the conformational distribution of trialanine, we combined UV-CD and H NMR spectroscopies. The temperature dependence of the conformationally sensitive maximum dichroism (Δε) and (3)J(H(α)H(N)) coupling constants of two amide protons (N- and C-terminal) was subjected to a global thermodynamic analysis based on simple two-state PPII↔β models. Interestingly, our results show that even small admixtures of alcohol (5% v/v) considerably change the spectral parameters, Δε(PPII) and Δε(β), as well as the enthalpic and entropic differences between the two states. For the central residue of trialanine in 5% glycerol, we obtained a gain in enthalpy favoring PPII of ΔΔH(n) = -4.80 kJ/mol and a compensating increase in entropy favoring the β-strand of ΔΔS(n) = -13.53[J/mol K]. This causes increases in -ΔG and slight increases in PPII content. Further addition of alcohol, however, reverses the trend in that it causes a destabilization of the hydration shell and a shift toward β-strand conformations. The combined manifold of ΔH and ΔS values obtained for the investigated binary mixtures and the pure aqueous solvent exhibits an excellent linear correlation, which reflects enthalpy-entropy compensation and a common transition temperature. The latter can be considered an indication of a weak binding between cosolvent and peptide. A comparison of infrared and Raman spectra of trialanine in water and in water-alcohol mixtures indeed reveals a close proximity between aliphatic side chains of alanine residues and alcohol molecules even for 5% (v/v) alcohol-water mixtures. Hence, our results provide the first experimental evidence for direct interactions between, e.g., glycerol and peptides in aqueous solutions, in line with the result of recent calculations by Vagenende et al. (Biochemistry 2009, 48, 11084-11096) but at variance with preferential exclusion theories.

Systematic choice of crosslinker and filler for pervaporation membrane: A case study with dehydration of isopropyl alcohol–water mixtures by polyvinyl alcohol membranes

Poly vinyl alcohol (PVOH) membrane, was crosslinked with 2, 4 and 6 mass% of four different kinds of crosslinkers i.e. glutaraldehyde (GLU), oxalic acid (OA), dimethylol urea (DMU) and tetra ethyl ortho silicate (TEOS) to produce four different kinds of crosslinked PVOH membranes termed here as PVGLU, PVOA, PVDMU and PVTEOS membrane, respectively. These membranes were first used for pervaporative separation of azeotropic feed concentration of 87.7 mass% of isopropyl alcohol (IPA) in water. Among all of these membranes PVOH membrane crosslinked with 2 mass% (of PVOH) GLU i.e. PVGLU2 was found to show optimum flux and water selectivity (79.75 g/m 2 h and 45.23, respectively, at 40 °C) for separation of this IPA–water azeotropic mixture. This PVGLU2 membrane was further filled with 2, 4, and 6 mass% hydrophilic aluminosilicate filler to produce three different filled membranes i.e. F2PVGLU2, F4PVGLU2 and F6PVGLU2, respectively. These three filled membranes were used for separation of the same azeotropic IPA–water mixtures and F6PVGLU2 membrane was found to show optimum flux and selectivity (109.84 g/m 2 h and 72.71, respectively, at 40 °C). This F6PVGLU2 membrane crosslinked with 2 mass% glutaraldehyde and filled with 6 mass% aluminosilicate filler showing optimum flux and selectivity for azeotropic IPA–water mixture was used for dehydration of IPA using IPA–water mixtures containing 75.87–99.36 mass% IPA in water. All of the filled and unfilled membranes synthesized were also characterized by various conventional methods.

Simultaneous determination of Maillard reaction impurities in memantine tablets using HPLC with charged aerosol detector

A gradient high performance liquid chromatographic (HPLC) method using charged aerosol detection (CAD) was developed for the simultaneous determination of impurities formed by the Maillard reaction in memantine tablets. These impurities were a memantine-lactose adduct (ML), a memantine-dimethylamino glycine adduct (DMAG), a memantine-galactose adduct (MGAL), and a memantine-glucose adduct (MGLU). The chromatographic separation was performed on a Synergy Hydro RP column (100 mm × 3 mm, 2.5 μm particles) from Phenomenex with gradient elution using mobile phases consisting of 0.6% (v/v) of heptafluorobuturic acid (HFBA) in two acetonitrile–isopropyl alcohol–water mixtures. The method validation for the impurities included linearity, accuracy by spike recovery, precision, limits of detection and quantitation, and robustness. The method was sensitive for these non-chromophoric impurities down to 0.4–0.6 μg/mL (0.02–0.03% of the memantine drug substance). The effect of mobile phase HFBA concentration on chromatographic resolution and peak shape was investigated, and the effect of sample diluent acidification on method accuracy via spike recovery was studied. The operational simplicity of the CAD detector for routine quality control has been demonstrated.