Aqueous Alcohol Mixtures Research Articles

SET-LRP of Bio- and Petroleum-Sourced Methacrylates in Aqueous Alcoholic Mixtures.

Single-electron transfer-living radical polymerization (SET-LRP) in "programmed" aqueous organic biphasic systems eliminates the judicious choice of solvent and also provides accelerated reaction rates. Herein, we report efforts to expand the monomer scope for these systems by targeting methacrylic monomers and polymers. Various environmentally friendly aqueous alcoholic mixtures were used in combination with Cu(0) wire catalyst, tris(2-dimethylaminoethyl)amine (Me6-TREN) ligand, and p-toluenesulfonyl chloride (Ts-Cl) initiator to deliver well-defined polymethacrylates from methyl methacrylate, butyl methacrylate, and other monomers derived from biomass feedstock (e.g., lactic acid, isosorbide, furfural, and lauric acid). The effect of water on the nature of the reaction mixture during the SET-LRP process, reaction rate, and control of the polymerization is discussed. The control retained under the reported conditions is demonstrated by synthesizing polymers of different targeted molar mass as well as quasi-block AB copolymers by "in situ" chain extension at high conversion. These results highlight the capabilities of SET-LRP to provide sustainable solutions based on renewable resources.

Composite Membranes with a Polyvinyltrimethylsilane Skin Layer for Separation of Water–Alcohol Mixtures

The paper presents the characteristics of a laboratory-made water-selective composite membrane with a selective layer of hydrophobic polyvinyltrimethylsilane (PVTMS) for use in the processes of vapor-phase membrane recovery of alcohols from dilute aqueous alcohol mixtures of biogenic origin. The support is a polyacrylonitrile ultrafiltration membrane, and the PVTMS skin layer of the resulting composite membrane has a thickness of 3 to 4 microns. The vapor transport and separation characteristics of the membrane for water–ethanol and water–butanol mixtures in the temperature range of 60–80°C have been studied. It has been shown that the membrane selectivity varies in the range of 23–39 for the water/ethanol pair or 100–140 for the water/butanol pair. A specific feature of the hydrophobic water-selective membrane as applied to the vapor-phase process is the stability of its characteristics due to the absence of swelling, in contrast to hydrophilic water-selective membranes whose characteristics substantially depend on the activity of water vapor. The process of vapor-phase membrane recovery of ethanol and butanol from dilute aqueous alcohol mixtures of biogenic origin with their initial concentrations of 10 and 1 wt %, respectively, has been mathematically modeled on the basis of the experimental data. The calculation results show that the composite membrane obtained makes it possible to concentrate ethanol and butanol to 95 and 98 wt % with degrees of recovery of more than 0.8 and more than 0.9, respectively.

Molecular Insight into the Liquid Propan-2-ol + Water Mixture.

The hydrogen bonding structure of the mixture propan-2-ol + water is analyzed at ambient conditions of temperature and pressure with molecular modeling and simulation techniques. A new force field for propan-2-ol is developed for this purpose on the basis of quantum chemical calculations and validated for a wide range of macroscopic properties. The basic mixing properties, excess volume and excess enthalpy, as well as the most important transport properties, that is, diffusion coefficients and shear viscosity, are considered to verify the suitability of the employed force fields for studying the complex behavior of this aqueous alcoholic mixture. Radial distribution functions and hydrogen bonding statistics are employed to characterize the hydrogen bond network and molecular clustering. Inhomogeneous mixing on the microscopic level, given by the presence of segregation pockets, is identified. The interrelation between the intriguing macroscopic behavior of this binary mixture and its microscopic structure is revealed.

Polyacrylamide "revisited": UCST-type reversible thermoresponsive properties in aqueous alcoholic solutions.

Combining experiments and all-atom molecular dynamics simulations, we study the conformational behavior of polyacrylamide (PAM) in aqueous alcohol mixtures over a wide range of temperatures. This study shows that even when the microscopic interaction is dictated by hydrogen bonding, unlike its counterparts that present a lower critical solution temperature (LCST), PAM shows a counterintuitive tunable upper critical solution temperature (UCST)-type phase transition in water/alcohol mixtures that was not reported before. The phase transition temperature was found to be tunable between 4 and 60 °C by the type and concentration of alcohol in the mixture as well as by the solution concentration and molecular weight of the polymer. In addition, molecular dynamics simulations confirmed a UCST-like behaviour of the PAM in aqueous alcoholic solutions. Additionally, it was observed that the PAM is more swollen in pure alcohol solutions than in 80% alcoholic solutions due to θ-like behaviour. Additionally, in the globular state, the size of the aggregates was found to increase with increasing solvent hydrophobicity and polymer concentration of the solutions. Above its phase transition temperature, PAM might be present as individual polymer chains in the coil state (≤10 nm). As PAM is a widespread polymer in many biomedical applications (gel electrophoresis, etc.), this finding could be of high relevance for many more practical applications in high performance pharmaceuticals and/or sensors.

Alcohol induced gelation of TEMPO-oxidized cellulose nanofibril dispersions.

Solvent-induced physical hydrogels of TEMPO-oxidized cellulose nanofibrils (OCNFs) were obtained from aqueous/alcoholic dispersions of fibrils in lower alcohols, namely, methanol, ethanol, 1-propanol and 2-propanol. The sol-gel transition occurs above a critical alcohol concentration of ca. 30 wt% for all alcohols tested. The rheological properties of the hydrogels depend on the nature of the alcohol: for ethanol, 1-propanol and 2-propanol the magnitude of the shear storage modulus follows the alcohol hydrophilicity, whilst methanol produces the weakest gels in the group. Above a second critical concentration, ca. 60 wt% alcohol, phase separation is observed as the gels undergo syneresis. Analysis of small-angle X-ray scattering data shows that the OCNFs may be modelled as rigid rods. In the presence of lower alcohols, attractive interactions between nanofibrils are present and, above the alcohol concentration leading to gelation, an increase of the OCNF cross-section is observed, suggesting alcohol induced aggregation of nanofibrils.

Two-Ply Composite Membranes with Separation Layers from Chitosan and Sulfoethylcellulose on a Microporous Support Based on Poly(diphenylsulfone-N-phenylphthalimide)

Two-ply composite membranes with separation layers from chitosan and sulfoethylcellulose were developed on a microporous support based on poly(diphenylsulfone-N-phenylphthalimide) and investigated by use of X-ray diffraction and scanning electron microscopy methods. The pervaporation properties of the membranes were studied for the separation of aqueous alcohol (ethanol, propan-2-ol) mixtures of different compositions. When the mixtures to be separated consist of less than 15 wt % water in propan-2-ol, the membranes composed of polyelectrolytes with the same molar fraction of ionogenic groups (-NH3+ for chitosan and -SO3− for sulfoethylcellulose) show high permselectivity (the water content in the permeate was 100%). Factors affecting the structure of a non-porous layer of the polyelectrolyte complex formed on the substrate surface and the contribution of that complex to changes in the transport properties of membranes are discussed. The results indicate significant prospects for the use of chitosan and sulfoethylcellulose for the formation of highly selective pervaporation membranes.

Mechanism of transformation of protons in the process of creating aqueous-alcoholic mixtures

Mechanism of transformation of protons in the process of creating aqueous-alcoholic mixtures

Self-assembly of t-butyloxycarbonyl protected dipeptide methyl esters composed of leucine, isoleucine, and valine into highly organized structures from alcohol and aqueous alcohol mixtures.

Short peptides composed of phenylalanine and sequences derived from amyloidogenic peptides have the ability to self-assemble to form nanostructures including hydrogels. The self-assembly of peptides composed of only hydrophobic amino acids and aliphatic protecting groups have not been investigated in detail. We have examined various aspects of nanostructures formed by N-terminal t-butyloxycarbonyl-protected aliphatic dipeptide methyl esters dissolved in various solvents. Scanning electron microscopic images indicate that depending on the sequence, position of the amino acid and solvent of dissolution, the peptides self-assemble into superstructures such as nanotubes and needles particularly from aqueous mixtures of organic solvents. Crystallization was not required for self-assembly into nanostructures. Circular dichroism and attenuated total internal reflection fourier transform infrared spectroscopy studies indicate that the peptides adopt β-conformation in the superstructures both in solution and solid state. The nanostructures composed of entirely aliphatic moieties have the ability to bind to aromatic dyes such as Rhodamine 6G, Nile red and Congo red. They also bind to Thioflavin T although the structures do not resemble amyloid fibrils. The powder X-ray diffraction patterns suggest distinctive packing of the monomers. These structures are stabilized by intermolecular hydrogen bonds and hydrophobic interactions resulting in superstructures containing long distance order and were devoid of hemolytic activity.

Evolution of the micro-structure of aqueous alcohol mixtures with cooling: A computer simulation study

We study by computer simulations aqueous ethanol and tert-butanol mixtures for temperatures below room temperature, from T=250K to T=150K, in order to monitor how concentration fluctuations and micro-segregation evolve with the lowering of temperature. Similarly to our recent study of aqueous-methanol mixtures [J. Chem. Phys. 145, 144502 (2016)], we find that concentration fluctuations tend to decrease - as monitored by the lowering of the k=0 value of the structure factors, while micro-segregation becomes more specific, in particular with a marked tendency of water to form short chain-like clusters, instead of large bulky nano-domains at higher temperatures. This clustering translates into a growing pre-peak in the water-water structure factors at k ≈ 0.5Å−1. The decrease of concentration fluctuations is also in agreement with the fact that calculated Kirkwood-Buff integrals tend to become ideal, in sharp contrast with the data for T=300K, in particular for aqueous-tbutanol mixtures. This near-ideality is a consequence of water forming supra-molecular linear clusters. We conjecture that the cooling of nano-structured mixtures produces a “transfer” of k=0 concentration fluctuation mode towards k≠0 mode, leading in particular to these supra-molecular water clusters.

Poly(N-isopropylacrylamide) Microgels under Alcoholic Intoxication: When a LCST Polymer Shows Swelling with Increasing Temperature.

Poly(N-isopropylacrylamide) (PNIPAM) microgel is a smart polymer that shows a volume phase transition temperature (VPTT) at around 32 °C in aqueous solutions, above which it collapses. In this work, combining experiments and molecular simulations, it is shown that PNIPAM microgels do not always exhibit a collapsed structure above the VPTT. Instead, PNIPAM in aqueous alcohol mixtures shows a two-step conformational transition, i.e., a collapse at low temperatures (T < 32 °C) and a reswelling when T > 50 °C. The present analysis indicates that delicate microscopic interaction details, together with the bulk solution properties, play a key role in dictating the reswelling behavior. Even when PNIPAM microgels swell with increasing T, this is not a standard upper critical solution behavior.

How does poly(N-isopropylacrylamide) trigger phase separation in aqueous alcohol?

Short chain alcohols, such as methanol and ethanol, are fairly well miscible in water over full mixing ratios. Moreover, when poly(N-isopropylacrylamide) is added in the same mixtures, the solution phase separates at low alcohol concentrations. From the fundamental understanding of phase separation within the mean-field picture, we can expect interaction parameter χ between water and alcohol to be significantly larger than unity. On the contrary, however, χ remains invariant and close to zero over full mixing ratios of aqueous alcohol mixtures. Here, we show how the preferential binding of poly(N-isopropylacrylamide) with alcohols facilitates local phase separation without altering bulk solution χ.

Negative rejection of nonionic dye in aqueous alcohol solutions during nanofiltration by hydrophobic membranes

This paper reports that nonionic dye (“Oil Red O”) is negatively rejected during nanofiltration of its aqueous ethanol solution by hydrophobic membranes made of high-permeability glassy polymers. This implies that the dye concentrates in the permeate region. A probable reason for the observed negative rejection is positive adsorption of the neutral dye molecules inside the membrane pores. Comparing samples of PTMSP- and PMP-based membranes we verify the slightly modified version of the “fine porous membrane” model proposed here. Based on our own experimental data for the rejection coefficient and the normalized flux (permeability) through both polymeric membranes in dependence on alcohol concentration under different values of applied pressure, we calculate the main physico-chemical parameters of these membrane systems, i.e. the diffusion and the equilibrium distribution coefficients of “Oil Red O” molecules inside the membrane. Comparing the theoretically predicted parameters to the experiment-based rejection-flux curves, we conclude that the PTMSP-based membrane is 4–11 times more permeable for the neutral dye than the PMP-based membrane, although both membranes have very similar values of the negative rejection coefficient. The diffusion coefficient of “Oil Red O” is 1.5–8 times higher inside the PTMSP membrane compared to the PMP membrane, while the distribution coefficients for both membranes are close to each other. It might mean that the PMP membrane has a denser structure than the PTMSP membrane. Both membranes can be effectively used to purify aqueous alcohol mixtures of different dyes.

Thermocapillary modulation of self-rewetting films

Whereas surface tension decreases linearly with temperature for most fluids, here we consider those that exhibit a well-defined minimum. Specifically, our study is motivated by dilute aqueous mixtures of long-chain alcohols, for which surface tension is typically assumed to be a quadratic function of temperature. Utilization of these so-called ‘self-rewetting fluids’ has grown significantly in the past decade, due to observations that heat transfer is enhanced in applications such as film boiling and pulsating heat pipes. With similar applications in mind, we investigate the dynamics of a thin film with quadratic surface tension which is subjected to a temperature modulation in the bounding gas. A model is developed within the framework of the long-wave approximation, and a time-averaged thermocapillary driving force for destabilization is uncovered that results from the nonlinear surface tension. Linear stability analysis of the nonlinear partial differential equation for the film thickness is used to determine the critical conditions at which this driving force destabilizes the film and numerical investigation of this evolution equation reveals that linearly unstable perturbations saturate to regular periodic solutions (when the modulational frequency is set properly). Properties of these flows such as bifurcation at critical points and long-domain flows, where multiple unstable linear modes interact, are also discussed.

Volumetric and optical properties of ACE inhibitor captopril in aqueous-alcoholic mixtures

Captopril is an angiotensin-converting enzyme (ACE) inhibitor that is used for the treatment of hypertension and congestive heart failure. This article addresses the accurate measurements of densities and refractive indices of solutions containing captopril in pure solvents such as water, methanol, ethanol and 1-propanol and aqueous mixtures of methanol, ethanol and propan-1-ol of 30%, 50% and 70% by volume in a wide range of drug concentration at 26°C. This article also includes the evaluation of apparent molar volume, partial molar volume at infinite dilution and transfer volumes. The concentration dependence of the refractive indices studied and respective fitting parameters have been reported. Different properties are interpreted in terms of intermolecular interactions, effect of drug on structure of solvent/solvent mixture and overall structural fittings in solutions.

Prediction of the surface tension of binary liquid mixtures of associating compounds using the Cubic Plus Association (CPA) equation of state

Abstract Accurate knowledge of the surface tension of liquid mixtures is of considerable importance in the development of chemical processes that involve mass and heat transfer across phase interfaces. Despite the significant progress made in the development of advanced equations of state (EOS) for accurate representation of thermophysical properties, as well as sophisticated models for the thermodynamic equilibrium of highly non-ideal mixtures, they nonetheless have been to a large extent underrepresented in the prediction and correlation of the surface tension of such systems. In the current work, a modified version of the Butler equation is adopted alongside the Cubic Plus Association (CPA) EOS, with the objective of predicting and correlating the surface tension of binary liquid mixtures of associating compounds. In doing so, the experimental data of aqueous and non-aqueous mixtures of alcohols, glycols, acids, and phenol, comprised of 238 data points belonging to 18 binary mixtures are studied. It is shown that by incorporation of an association term based on the Wertheim's first-order thermodynamic perturbation theory, the CPA EOS can satisfactorily predict the values of surface tension with an AARD of only 9.78%, compared with deviations of 73.87% and 28.38% obtained for the Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) EOSs, respectively. Also, a major advantage of the proposed model is its inherent capability to simultaneously estimate the composition of the surface phase alongside the mixture surface tension. In addition, with only one adjusted binary parameter, AARDs of 5.29%, 7.09%, and 11.02% are obtained for the correlation of the experimental data using the CPA, SRK, and PR EOSs, respectively.

How does Poly(N-isopropylacrylamide) Trigger Phase Separation in Aqueous Alcohol?1, "Высокомолекулярные соединения. Серия С"

Abstract - Short chain alcohols, such as methanol and ethanol, are fairly well miscible in water over full mixing ratios. Moreover, when poly(N-isopropylacrylamide) is added in the same mixtures, the solution phase separates at low alcohol concentrations. From the fundamental understanding of phase separation within the mean-field picture, we can expect interaction parameter between water and alcohol to be significantly larger than unity. On the contrary, however, remains invariant and close to zero over full mixing ratios of aqueous alcohol mixtures. Here, we show how the preferential binding of poly(N-isopropylacrylamide) with alcohols facilitates local phase separation without altering bulk solution .

Diffusion in Multicomponent Liquids: From Microscopic to Macroscopic Scales.

In spite of considerable research on the nature of aqueous alcohol mixtures that are characterized by microscopic inhomogeneity or incomplete mixing at the molecular level, transport properties have received little attention. We report the results of a study on diffusion in the ternary mixture of water with two alcohols, that is, water + methanol + ethanol, which is investigated on microscopic and macroscopic scales by means of molecular simulation and Taylor dispersion experiments. A novel protocol is developed for the comparison of mutual diffusion coefficients sampled by two fundamentally different approaches, which allows for their critical analysis. Because of complex intermolecular interactions, given by the presence of hydrogen bonding, the analysis of transport processes in this mixture is challenging for not only on the microscopic scale for simulation techniques but also on the macroscopic scale due to unfavorable optical properties. Binary limits of the Fick diffusion matrix are used for validation of the experimental ternary mixture results together with the verification of the validity of the phenomenological Onsager reciprocal relations. The Maxwell-Stefan diffusion coefficients and the thermodynamic factor are sampled by molecular simulation consistently on the basis of given force field models. The protocol for the comparison of the results from both approaches is also challenging because Fick diffusion coefficients of ternary mixtures depend on the frame of reference. Accordingly, the measured coefficients are transformed from the volume-averaged to the molar-averaged frame of reference, and it is demonstrated that both approaches provide not only similar qualitative behavior along two concentration paths but also strong quantitative agreement. This coordinated work using different approaches to study diffusion in multicomponent mixtures is expected to be a significant step forward for the accurate assessment of cross-diffusion.

Further Numerical Analyses on the Solubility of Sulfapyridine in Ethanol + Water Mixtures

Background: Dissolution thermodynamic quantities of sulfapyridine (SP) have been reported in the literature for aqueous alcoholic mixtures. Nevertheless, no attempts to evaluate the preferential solvation of this drug in this binary system, have been reported. In this way, the inverse Kirkwood-Buff integrals (IKBI) were used to evaluate this behavior in solution. Methods: Solubility data for SP dissolved in binary ethanol (EtOH) + water mixtures at various temperatures were mathematically represented using the Jouyban-Acree (J-A) model. The preferential solvation parameters of SP by EtOH (δx1,3) in EtOH + water mixtures were obtained from some thermodynamic properties of the mixtures by means of the IKBI method. Results: Solubility of SP in EtOH + water mixtures is adequately described by the J-A model in second order. Moreover, SP is sensitive to specific solvation effects, so the δx1,3 values are negative in water-rich and EtOH-rich mixtures indicating preferential solvation by water in these mixtures. By contrary, δx1,3 values are positive in the range 0.24 < x1 < 0.53 indicating preferential solvation by EtOH in these mixtures. Conclusion: It can be assumed that in water-rich mixtures the hydrophobic hydration around the aromatic rings plays a relevant role in the solvation. The higher drug solvation by EtOH in mixtures of similar solvent proportions could be due to polarity effects. Moreover, in EtOH + water mixtures SP could be acting as a Lewis acid with the EtOH molecules and in EtOH-rich mixtures the drug could be acting as a Lewis base with water molecules.

Encapsulation of the elderberry fruit anthocyanins by spray drying

Spray-dried forms of anthocyanins were prepared in a maltodextrin matrix. The anthocyanins were extracted by maceration of elderberry fruits in 0.1 M HCl followed by extract filtration through a paper filter. The extract was partially purified by solid phase extraction in a column filled with styrene-divinylbenzene copolymer beads (Sepabeads SP859/L) or in syringe cartridges with C18 silica (BioChemMack ST, Moscow, RF) followed by re-extraction with aqueous HCl and alcohol mixtures. The procedure of reversed-phase HPLC determination of the extracted anthocyanin type is discussed in comparison to HILIC method in DIOL silica columns. The latter method was shown to be preferable to avoid systematic errors in the anthocyanin type determination. Solidphase extraction in syringe cartridges gave samples with very high anthocyanins concentration (up to 70 g of cyanidin-3-glucoside chloride equivalent). When using the copolymer sorbent, the concentration was somewhat lower: up to 27 g/l. After spray drying red powder samples with anthocyanins content more than 2% were prepared, although freeze drying gave only dark resin. The red color of the samples indicates the space separation of flavylium ions in the solid state by radicals of the maltodextrin background.

(Liquid + liquid) equilibria of four alcohol–water systems containing 1,8-cineole at T = 298.15 K

As an eco-friendly compound from essential oils, 1,8-cineole (cineole, eucalyptol) has the potential to replace the ozone depleting industrial solvents. This paper presents experimental (liquid+liquid) equilibrium (LLE) data for four alcohol–water systems containing 1,8-cineole. To evaluate the phase equilibrium properties of 1,8-cineole in aqueous alcohol mixtures, LLE values for the ternary systems (water+methanol or ethanol or 1-propanol or 1-butanol+1,8-cineole) were determined with a tie-line method at T=298.15K under atmospheric pressure. The well-known Hand, Bachman and Othmer–Tobias equations were used to test the reliability of the experimental results. The binodal curves and distribution ratios of alcohol in the mixtures are shown and discussed. The experimental LLE values were satisfactorily correlated by the NRTL and UNIQUAC models.