Alcohol-water Mixtures Research Articles

Deposition of silicon dioxide antireflection coatings on glass by sol-gel method in the presence of Pluronic® F127 block-copolymer

Hydrolysis of tetraethoxysilane in the presence of Pluronic® F127 block-copolymer in a water-alcohol mixture was used to obtain sol-formulations from which antireflection coatings were deposited onto silicate glass by the dip-coating method and then calcined at high temperatures (200–500°C). Electron spectroscopy was used to study the dependence of the optical transmission of glass samples with a coating on the concentration of Pluronic® F127 in the starting sol, introduction of organic additives (toluene) into the sol, and calcination temperature of the glasses obtained. The refractive index and hardness of the film coatings were determined and their surface structure was assessed.

Hydrogen bonding in DPD: application to low molecular weight alcohol-water mixtures.

In this work we propose a computational approach to mimic hydrogen bonding in a widely used coarse-grained simulation method known as dissipative particle dynamics (DPD). The conventional DPD potential is modified by adding a Morse potential term to represent hydrogen bonding attraction. Morse potential parameters are calculated by a mapping of energetic and structural properties to those of atomistic scale simulations. By the addition of hydrogen bonding to DPD and with the proposed parameterization, the volumetric mixing behavior of low molecular weight alcohols and water is studied and experimentally observed negative volume excess is successfully predicted, contrary to the conventional DPD implementation. Moreover, the density-dependent DPD parameterization employed provides the asymmetrical shapes of the excess volume curves. In addition, alcohol surface enrichment at the air interface and self-assembly in the bulk is studied. The surface concentrations of alcohols at the air interface compare favorably with the experimental observations at all bulk-phase alcohol fractions and, in consonance with experiment, some clustering is observed.

Ultrafast SET-LRP of hydrophobic acrylates in multiphase alcohol–water mixtures

A multiphase SET-LRP system using thein situgenerated Cu(0) by reduction of Cu(ii)Br2with NaBH4in various alcohols containing water was developed and used for SET-LRP of hydrophobic acrylates. From left to right: a solution of methanol/water containing Cu(ii)Br2, the same solution after addition of BA and its SET-LRP.

Polyelectrolyte conformational transition in aqueous solvent mixture influenced by hydrophobic interactions and hydrogen bonding effects: PAA–water–ethanol

Molecular dynamics simulations of poly(acrylic acid) PAA chain in water–ethanol mixture were performed for un-ionized and ionized cases at different degree-of-ionization 0%, 80% and 100% of PAA chain by Na+ counter-ions and co-solvent (ethanol) concentration in the range 0–90vol% ethanol. Aspects of structure and dynamics were investigated via atom pair correlation functions, number and relaxation of hydrogen bonds, nearest-neighbor coordination numbers, and dihedral angle distribution function for back-bone and side-groups of the chain. With increase in ethanol concentration, chain swelling is observed for un-ionized chain (f=0) and on the contrary chain shrinkage is observed for partially and fully ionized cases (i.e., f=0.8 and 1). For un-ionized PAA, with increase in ethanol fraction ϕeth the number of PAA–ethanol hydrogen bonds increases while PAA–water decreases. Increase in ϕeth leads to PAA chain expansion for un-ionized case and chain shrinkage for ionized case, in agreement with experimental observations on this system. For ionized-PAA case, chain shrinkage is found to be influenced by intermolecular hydrogen bonding with water as well as ethanol. The localization of ethanol molecules near the un-ionized PAA backbone at higher levels of ethanol is facilitated by a displacement of water molecules indicating presence of specific ethanol hydration shell, as confirmed by results of the RDF curves and coordination number calculations. This behavior, controlled by hydrogen bonding provides a significant contribution to such a conformational transition behavior of the polyelectrolyte chain. The interactions between counter-ions and charges on the PAA chain also influence chain collapse. The underlying origins of polyelectrolyte chain collapse in water–alcohol mixtures are brought out for the first time via explicit MD simulations by this study.

Structure and Hydrogen Bonding of Water in Polyacrylate Gels: Effects of Polymer Hydrophilicity and Water Concentration.

The ability to tune the hydrophilicity of polyacrylate copolymers by altering their composition makes these materials attractive candidates for membranes used to separate alcohol-water mixtures. The separation behavior of these polyacrylate membranes is governed by a complex interplay of factors such as water and alcohol concentrations, water structure in the membrane, polymer hydrophilicity, and temperature. We use molecular dynamics simulations to investigate the effect of polymer hydrophilicity and water concentration on the structure and dynamics of water molecules in the polymer matrix. Samples of poly(n-butyl acrylate) (PBA), poly(2-hydroxyethyl acrylate) (PHEA), and a 50/50 copolymer of BA and HEA were synthesized in laboratory, and their properties were measured. Model structures of these systems were validated by comparing the simulated values of their volumetric properties with the experimental values. Molecular simulations of polyacrylate gels swollen in water and ethanol mixtures showed that water exhibits very different affinities toward the different (carbonyl, alkoxy, and hydroxyl) functional groups of the polymers. Water molecules are well dispersed in the system at low concentrations and predominantly form hydrogen bonds with the polymer. However, water forms large clusters at high concentrations along with the predominant formation of water-water hydrogen bonds and the acceleration of hydrogen bond dynamics.

Methods for the extraction of biologically active substances from medicinal plants based on an example of St. John’s wort components

The efficiency of extraction of biologically active substances from common St. John’s wort (Hypericum perforatum L.) under varied conditions was compared in order to optimize a sample preparation procedure. The extraction with water and water–alcohol solutions under static conditions and with stirring was examined; the effect of ultrasonic treatment and extraction with water and water–alcohol mixtures under dynamic conditions at elevated temperature and pressure and the extraction with supercritical carbon dioxide were studied. It was established that, in the extraction of biologically active substances from plant materials, the chemical affinity of an extractant the extracted component is of primary importance; an increase in the pressure under dynamic conditions is the second factor in importance, which increases the efficiency of extraction.

Self-assembly of a peptide with a tandem repeat of the Aβ16-22 sequence linked by a β turn-promoting dipeptide sequence.

Amyloid deposits have been found to be abundant in patients with Alzheimer's disease due to fibril formation by the Aβ peptides. Peptide Aβ16-22, comprising of the seven-residue segment KLVFFAE, spanning residues 16-22 of the full length Aβ42 peptide, aggregates to form fibrils or other nanostructures in isolation, depending on the conditions of dissolution and incubation. In this study, we have examined the self-assembly of PAβ, a tandem repeat peptide of the Aβ16-22 sequence, joined by a β-turn-inducing sequence Asn-Gly. To study the effect of various solvents on the self-association, hexafluoroisopropanol (HFIP), trifluoroethanol (TFE) and methanol were used. The peptide was also incubated in fibril-promoting conditions of 20% fluorinated alcohol-water mixtures which form dynamical solvent clusters, as well as in 20% MeOH-water mixture which does not form solvent clusters. Secondary structural studies suggest the presence of β-structures. Electron microscopic images indicate that fibril formation occurs in a time-dependent manner, under different conditions of solvent composition. Thioflavin-T fluorescence studies confirm the presence of amyloid fibrils in the aggregates. Although the insertion of the Asn-Gly sequence has not facilitated the formation of an ideal Type I' rigid turn, the intramolecular interactions aid the formation of a flexible β-turn conformation, with twisted β-sheets. Interactions between the intermolecular β-sheets result in the formation of amyloid fibrils. Organic solvents appear to play an important role in modulating self-assembly of peptide PAβ during fibril formation. Studies on β-hairpin engineered amyloidogenic peptides could lead to knowledge about suitable conditions for generating a diverse range of polymorphic structures.

Atypical wetting behaviour of alcohol–water mixtures on hydrophobic surfaces

Abstract Methanol, ethanol, n -propanol and their aqueous solutions are widely used in many industrial applications where wettability is one of the most important parameters. This project was focused on the experimental study of the wetting behaviour of these mixtures on two similar hydrophobic surfaces in the full concentration range. Based on the measurements of dynamic surface tension and dynamic liquid drop spreading we proved the stable composition of liquid layers on the solid–liquid and liquid–air interfaces. Likewise, in bulk liquid the existence of small aggregates consisting of water and alcohol molecules is assumed. This complex internal structure of aqueous solutions of short chain alcohols influences the surface properties of these solutions and explains the higher contact angles when compared to pure liquids with similar surface tension.

Raman Spectroscopy of Water-Ethanol Solutions: The Estimation of Hydrogen Bonding Energy and the Appearance of Clathrate-like Structures in Solutions.

The structure of aqueous alcohol solutions at the molecular level for many decades has remained an intriguing topic in numerous theoretical and practical investigations. The aberrant thermodynamic properties of water-alcohol mixtures are believed to be caused by the differences in energy of hydrogen bonding between water-water, alcohol-alcohol, and alcohol-water molecules. We present the Raman scattering spectra of water, ethanol, and water-ethanol solutions with 20 and 70 vol % of ethanol thoroughly measured and analyzed at temperatures varying from -10 to +70 °C. Application of the MCR-ALS method allowed for each spectrum to extract contributions of molecules with different strengths of hydrogen bonding. The energy (enthalpy) of formation/weakening of hydrogen bonds was calculated using the slope of Van't Hoff plot. The energy of hydrogen bonding in 20 vol % of ethanol was found the highest among all the samples. This finding further supports appearance of clathrate-like structures in water-ethanol solutions with concentrations around 20 vol % of ethanol.

In-situ synthesis of Ni/N-doped CNFs-supported graphite disk as effective immobilized catalyst for methanol electrooxidation

In this study, a facile, controllable, and efficient process (electrospinning followed by calcination at 1100 °C under argon atmosphere) is developed for in-situ synthesis of Ni/N-CNFs catalyst as thin film immobilized on graphite disk. Moreover, the influence of nitrogen content on the catalytic activity of the supported Ni-doped CNFs toward methanol oxidation was investigated. The composition and morphology of the prepared catalysts were characterized by XRD, EDX, FE-SEM and TEM techniques. The electrocatalytic activity and stability were evaluated by cyclic voltammetry (CV) and chronoamperometry, respectively. Compared to the powder form, the results indicated that the proposed in-situ immobilization of the introduced nanofibers on graphite disk reveals distinct enhancement in the electrocatalytic activity due to merging of the underneath nanofibers with the graphite support which eliminates the interfacial resistance. Numerically, the detected maximum current density was 270.44 and 80.59 mA/cm2 for Ni/N-CNFs/graphite and unsupported nanofibers, respectively. Moreover, the obtained results have also showed that nitrogen doping effectively enhances the electrocatalytic activity and stability of Ni/CNFs toward methanol oxidation in the alkaline medium. However, due to the influence of methanol content on the water-alcohol mixture fluidity, the optimum methanol concentration was observed to be 0.5 and 5.0 M for the supported and unsupported nanofibers, respectively. Overall, this study opens new avenue to prepare one-pot current collector/electrode plate to be utilized in the fuel cell technology.

Equation of state for water-alcohol mixtures over a wide range of state variables

Coefficients of the three-parameter polynomial equation of states are determined from experimental data on the (p, ρ, T, x) relationship for water-aliphatic alcohol (methanol, ethanol, and n-propanol) mixtures in the liquid and vapor phases and in the supercritical state: expansions of compressibility factor Z = p/RTρm into series in powers of reduced density ω = ρm/ρmcr; reduced temperature τ = T/Tcr and composition x (as the mole fraction of alcohol), \(Z = p/RT\rho _m = 1 + \sum\nolimits_{i = 1}^m {\sum\nolimits_{j = 0}^n {\sum\nolimits_{k = 0}^s {a_{ijk} \omega ^i \tau ^{ - j} x^k ;} } } p = RT\rho _m = [1 + \sum\nolimits_{i = 1}^m {\sum\nolimits_{j = 0}^n {\sum\nolimits_{k = 0}^s {a_{ijk} \omega ^i \tau ^{ - j} x^k } } ]} \). The mean percentage errors of the calculated pressure values relative to the experimental values are 2% (liquid phase), 0.7% (vapor phase), and 0.5% (supercritical fluid).

Novel Au/TiO2 photocatalysts for hydrogen production in alcohol–water mixtures based on hydrogen titanate nanotube precursors

In this study, a series of titania nanorods with different phase compositions and surface areas were prepared by calcination of hydrogen titanate (H2Ti3O7) nanotubes at temperatures up to 1000°C. Gold nanoparticles were subsequently deposited on the obtained TiNTx (x=calcination temperature) nanorod supports at loadings between 0.5 and 2.0wt.%, and also onto a commercially available mixed-phase titania support (Degussa P25). TEM, XRF, UV–Vis, XPS and photoluminescence measurements confirmed the presence of gold nanoparticles of mean size 4–7nm on the surface of the Au/TiNTx (x=350–800) and Au/P25 photocatalysts, which suppressed electron–hole pair recombination in TiO2 under UV and created cathodic sites for hydrogen evolution. Hydrogen production tests were conducted on the Au/TiNTx and Au/P25 photocatalysts in various alcohol–water mixtures under UV excitation (6.5mWcm−2) with no external bias applied. The impact of the gold loading and the calcination temperatures on the structural, physico-chemical and photocatalytic properties of the TiNTx nanorods was investigated, and a comparison to P25 was made. A 0.5wt.% Au/TiNT600 photocatalyst demonstrated excellent H2 production activity in all the alcohol–water systems, performing similarly to a 1.5wt.% Au/P25 reference photocatalyst. For both the 0.5wt.% Au/TiNT600 and 1.5wt.% Au/P25 photocatalysts, H2 production rates decreased in the order triol (glycerol)>diol (1,2-ethanediol≈1,2-propanediol)>ethanol>1-propanol. Good correlations were found between the H2 production rates and alcohol properties such as the number of hydroxyl groups, polarity or standard oxidation potential.

Measurements and correlations of density and viscosity for short chain (C1–C3) n-alcohol–water mixtures in the temperature range from 350.7 K to 476.2 K at pressures up to 40 MPa

Densities and viscosities of short chain (C1–C3) n-alcohol–water mixtures have been measured in the entire range of composition at temperature ranges (350.7 to 476.2K) and at pressures up to 40MPa. The Eyring theory for viscosity incorporated with the Patel–Teja (PT) equation of state was applied to the correlation of experimental viscosities, when Redlich–Kister (RK) or van der Waals one fluid (vdW1) mixing rules were applied to mixtures. The two binary interaction parameters of these mixing rules were determined by fitting of viscosity data. Moreover, the density values were also evaluated using the parameters which were determined in viscosity correlation. The Eyring+PT+RK model gave better correlation of viscosities for alcohol–water mixtures within a deviation of 1.5% (3.9% for the Eyring+PT+vdW1 model). The Eyring+PT+RK model was found to be also superior in terms of density evaluation so as to be the deviation within 4.8% (18.7% for the Eyring+PT+vdW1 model).

Effect of TiO2 polymorph and alcohol sacrificial agent on the activity of Au/TiO2 photocatalysts for H2 production in alcohol–water mixtures

This study compares the performance of 5 different Au/TiO2 photocatalysts for H2 production in alcohol–water mixtures under UV excitation, placing particular emphasis on the role of the TiO2 support and alcohol sacrificial reagent. 1.5wt.% Au/TiO2 photocatalysts were prepared by the deposition–precipitation with urea method, using P25 TiO2 (85% anatase and 15% rutile, 49m2g−1), sol–gel anatase (39m2g−1), hydrothermally synthesised anatase (115m2g−1), commercial brookite (33m2g−1) and hydrothermally synthesised rutile (29m2g−1) as supports. UV–Vis, TEM, XRD, XPS and Au L3-edge EXAFS characterisation studies confirmed the presence of gold nanoparticles of mean size 5–10nm on all the Au/TiO2 photocatalysts, which generated intense localised surface plasmon resonances (LSPRs) centred between 560 and 590nm. Gold nanoparticle deposition suppressed electron–hole pair recombination in each TiO2 support following UV excitation, and created cathodic sites on TiO2 for H2 evolution. Photocatalytic H2 production tests were conducted in water, methanol–water, ethanol–water, ethylene glycol–water and glycerol–water mixtures (alcohol concentration 10vol.%) at a UV flux of 6.5mWcm−2. H2 production rates decreased in the order Au/P25>Au/anatase SG≈Au/brookite>Au/anatase HT≫Au/rutile HT when the rates were normalised against photocatalyst surface area. For each Au/TiO2 photocatalyst, the rates decreased in the order glycerol>ethylene glycol>methanol>ethanol. Good correlations were established between H2 production rates and the number of hydroxyl groups, polarity and relative hole scavenging ability of the alcohols. Results improve knowledge about the role of sacrificial reagents in photocatalytic hydrogen production.

Effect of copper nanoclusters on the tribological properties of steel-steel friction pair in alcohol aqueous solutions

The purpose of this study is to investigate the influence of the alcohol atomicity on the self-organizing control capability in order to achieve the wearlessness effect in the friction pair of steel-steel. The copper-containing lubricant compositions are prepared in the electrolysis of the aqueous solutions of polyatomic alcohols with a copper anode in the ultrasonic field (complex processing). The laboratory testing of the tribological behavior of the lubricating compositions is carried out on four-ball machine using balls of SH-15 steel according to GOST 9490-75. Tribological properties of steel-steel friction pair are studied on the front friction machine AE-5. The copper particle size is defined by the sedimentation analysis method using the disk centrifuge of CPS Disc Centrifuge Model DC 24000 brand in the aqueous solutions of polyatomic alcohols. The topographic studies of the nanocluster metal structures are performed with the scanning probe microscope (SPM) Solver P 47 H in the semi-contact mode of the atomic force microscopy (AFM). The topographic investigations of a servovit film are conducted with the use of the scanning atomic force and power microscope of Compact AFM PHYWE . It is shown that the time increment of the integrated processing of a water-alcohol mixture leads to the strengthening of the antiwear properties of lubricant compositions. Increasing alcohol atomicity facilitates the implementation of the selective transfer, thus reducing wear and the transition time in the wearlessness mode. The resulting molecular ligand copper clusters with an average size of 25 nm are characterized by high uniformity. Thus, the friction track represents rather ironed surface with low roughness.

The roles of metal co-catalysts and reaction media in photocatalytic hydrogen production: Performance evaluation of M/TiO2 photocatalysts (M = Pd, Pt, Au) in different alcohol–water mixtures

M/TiO2 photocatalyst activity for H2 production depends on both the metal co-catalyst (M) and the reaction medium. To quantify such effects, we compared the performance of M/TiO2 photocatalysts (M=Pd, Pt, Au) for H2 production in different alcohol–water mixtures under UV excitation. Photocatalysts were prepared using Degussa P25 TiO2 at metal loadings of 0.5 and 1wt.% for Pd, 1wt.% for Pt and 1wt.% for Au. TEM, UV–Vis, XPS and EXAFS analyses confirmed the presence of supported metal nanoparticles of size ∼2, 1.3 and 5.4nm for Pd/TiO2, Pt/TiO2 and Au/TiO2, respectively. Photoluminescence data established that the metal co-catalysts effectively suppressed electron–hole pair recombination in TiO2 following photo-excitation. The activities of the M/TiO2 photocatalysts for H2 production were evaluated in a wide range of alcohol–water mixtures (alcohol concentration 10vol.%) under UV (365nm, 5mWcm−2). H2 production rates in the alcohol–water mixtures were dependent on (i) the metal co-catalyst; (ii) the co-catalyst loading; and (iii) the alcohol type. Co-catalyst activity followed the order Pd>Pt≈Au. The highest H2 production rates were achieved for the 1wt.% Pd/TiO2 photocatalyst in glycerol–water mixtures (47.5mmolg−1h−1) and 1,2-ethanediol–water mixtures (44.5mmolg−1h−1). H2 production rates decreased in the order glycerol>1,2-ethanediol>1,2-propanediol>methanol>ethanol>2-propanol>tert-butanol≫water. For each M/TiO2 photocatalyst, correlations were established between the rate of H2 production and specific alcohol properties, especially alcohol polarity and the exponential of the alcohol oxidation potential.

Laser-induced capillary effect in thin layers of water-alcohol mixtures.

The effect of droplet formation in thin layers of water-alcohol mixtures upon laser heating was studied. The droplet growth in the laser beam is governed by the surface tension gradient, which induces solutocapillary flows from the periphery to the center of the heated area. This gradient arises due to the local increase in surface tension caused by the evaporation of alcohol from the heated area of the layer. The experimental results have shown that the increase in the initial concentration of water in the mixture gives rise to the increase in droplet size. However, the increase in the power of laser irradiation leads to a decrease in the droplet growth rate. A simplified one-dimensional model of droplet growth is developed. The model involves the dependence of surface tension on both the temperature and concentration of components in the mixture, as well as the evaporation and condensation of alcohol. The experimental results are compared with those obtained using numerical simulations. A reasonable agreement between experimental and numerical results was shown.

Direct effect of tetrahedral alcohol species on the SPB of gold colloids: a deconvolution study

Aqueous gold colloids with a mean diameter of 15.4 ± 1.5 nm have been transferred into a range of water–alcohol mixtures. The influence of these mixtures (methanol, ethanol, 2-propanol, and tert-butanol), which present different hydrophobic properties, on the surface plasmon band of gold nanoparticles has been studied. Shifts of gold nanoparticles’ surface plasmon band (SPB) depend on the number of methyl groups and hydrophobic character of the alcohol molecule. Results from deconvolution analysis are explained considering variations on the grade of alcohol adsorption on the nanoparticle surface. TEM images indicate aggregation of the nanoclusters in mixtures of 2-propanol and tert-butanol. ζ potential measurements support the exchange of citrate ions by alcohol molecules, which in turn reflects the existence of an additional electrostatic component.

Effect of membrane and process characteristics on cost and energy usage for separating alcohol-water mixtures using a hybrid vapor stripping-vapor permeation process

BACKGROUND Alcohols, including ethanol and butanol, are receiving increased attention as renewable liquid biofuels. Alcohol concentrations may be low in a biological process due to product inhibition and, for non-starch feedstocks, limited substrate concentrations. The result is high separation energy demand by conventional distillation scenarios, despite favorable vapor–liquid equilibrium and, for butanol, partial miscibility with water. A hybrid vapor stripping–vapor permeation process, termed membrane assisted vapor stripping (MAVS), incorporating a fractional condensation step was found to be at least 65% more energy efficient than conventional distillation approaches. The effect of process design, component performance, and capacity changes on the energy usage and processing cost of MAVS systems for separating ethanol, 1-butanol, and acetone/butanol/ethanol (ABE) mixtures from water was studied. RESULTS For the recovery of 1-butanol from a 1 wt% aqueous solution, the 99.5 wt% 1-butanol product contained 7.0 times as much heating value energy as the MAVS process required to recover and dry it. The calculated cost to perform this separation was 0.126 US$ kg−1-product (0.102 US$ L−1) for a heating value cost of 3.69 US$ GJ−1, far below the current values for crude oil and conventionally-produced ethanol. Energy (electricity, natural gas) was 23% of this cost. The largest capital cost item was the compressor on the overhead vapor stream from the stripping column. Capital costs for membranes/modules was the 6th highest cost category, representing only 4% of the capital cost. A 10-fold increase in membrane cost caused the cost of production to increase 38%. CONCLUSION Hybrid MAVS processes are an energy- and cost-efficient means to recover alcohols from water. Despite recent fluctuations, fossil fuel costs are projected to increase. Thus processes utilizing mechanical energy to recapture and transfer thermal energy, including MAVS, should have a greater cost advantage in the future. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

A highly tunable and fully biocompatible silk nanoplasmonic optical sensor.

Novel concepts for manipulating plasmonic resonances and the biocompatibility of plasmonic devices offer great potential in versatile applications involving real-time and in vivo monitoring of analytes with high sensitivity in biomedical and biological research. Here we report a biocompatible and highly tunable plasmonic bio/chemical sensor consisting of a natural silk protein and a gold nanostructure. Our silk plasmonic absorber sensor (SPAS) takes advantage of the strong local field enhancement in the metal-insulator-metal resonator in which silk protein is used as an insulating spacer and substrate. The silk insulating spacer has hydrogel properties and therefore exhibits a controllable swelling when exposed to water-alcohol mixtures. We experimentally and numerically show that drastic spectral shifts in reflectance minima arise from the changing physical volume and refractive index of the silk spacer during swelling. Furthermore, we apply this SPAS device as a glucose sensor with a very high sensitivity of 1200 nm/RIU (refractive index units) and high relative intensity change.