The bulk properties of the water-dimethylsulfoxide system at 278–323.15 K and atmospheric pressure

The densities of water-dimethylsulfoxide (DMSO) mixtures were measured over the temperature range 278–323.15 K and over the whole range of compositions at atmospheric pressure. The partial molar volumes of water and dimethylsulfoxide, mixture volumetric thermal expansion coefficients, and partial molar volumetric thermal expansion coefficients of the components were calculated. The composition dependences of the density of the mixture passed a maximum at x ～ 0.6 at all temperatures (x is the mole fraction of dimethylsulfoxide). The composition dependences of the partial molar volumes of water and DMSO also passed extrema.     

The effect of UV irradiation on air/water interfacial activity of Tween 20–coumarin conjugates

In order to obtain photo-sensitive surfactants, coumarin derivatives were covalently attached, through either ester bond or ether bond, to hydroxyl groups located at the ends of PEO segments of Tween 20. The molar ratios of Tween 20 to coumarin residues in both Tween 20–coumarin conjugate having ester bond (TCES) and ether bond (TCET) were about 1:1 despite the excess coumarin in the reaction mixture. The photo-dimerization degree was in the order of TCET?>?TCES?>?a free coumarin derivative. And the air/water interfacial activity was in the order of TCET?>?Tween 20?>?TCES. The interfacial activities of TCES and TCET increased with the UV irradiation time. This is possibly because the coumarin residues of TCES and TCET are photo-dimerized to produce Gemini surfactant-like dimeric surfactants. The photo-induced change in the interfacial activity of TCES was slightly greater than that of TCET, probably due to the difference in the length, the polarity, and the flexibility of the linker between two monomeric conjugates of Gemini-like dimeric surfactants.     

Effect of volume concentration and temperature on viscosity and surface tension of graphene–water nanofluid for heat transfer applications

In the present study, the effect of volume concentration (0.05, 0.1 and 0.15 %) and temperature (10–90 °C) on viscosity and surface tension of graphene–water nanofluid has been experimentally measured. The sodium dodecyl benzene sulfonate is used as the surfactant for stable suspension of graphene. The results showed that the viscosity of graphene–water nanofluid increases with an increase in the volume concentration of nanoparticles and decreases with an increase in temperature. An average enhancement of 47.12 % in viscosity has been noted for 0.15 % volume concentration of graphene at 50 °C. The enhancement of the viscosity of the nanofluid at higher volume concentration is due to the higher shear rate. In contrast, the surface tension of the graphene–water nanofluid decreases with an increase in both volume concentration and temperature. A decrement of 18.7 % in surface tension has been noted for the same volume concentration and temperature. The surface tension reduction in nanofluid at higher volume concentrations is due to the adsorption of nanoparticles at the liquid–gas interface because of hydrophobic nature of graphene; and at higher temperatures, is due to the weakening of molecular attractions between fluid molecules and nanoparticles. The viscosity and surface tension showed stronger dependency on volume concentration than temperature. Based on the calculated effectiveness of graphene–water nanofluids, it is suggested that the graphene–water nanofluid is preferable as the better coolant for the real-time heat transfer applications.     

Vibrational sum-frequency generation at protein modified air–water interfaces: Effects of molecular structure and surface charging

Protein and surfactant modified air–water interfaces are an important model system for colloid science as many applications for example aqueous foams in food products rely on our knowledge and ability to tune molecular structures at these interfaces. That is because interfaces are a fundamental building block in the hierarchical structure of foam, where in fact the molecular level can determine properties on larger length scales. For that reason it is of great importance to increase our ability to study air–water interfaces with molecular level probes and to obtain not only information on coverage but also direct information on interfacial composition, molecular order, orientations as well as information on the charged state of an interface. Vibrational sum-frequency generation (SFG) is a powerful tool that can help to address these issues and is inherently surface sensitive. In this contribution we will review recent developments in the use of SFG for studies of biomolecules at aqueous interfaces and discuss current issues with the interpretation of SFG spectra from electrified interfaces. In order to guide interpretations from interface spectroscopy we invoke the use of complementary methods such as ellipsometry and zetapotential measurements of bulk molecules.     

Excess volume and surface tension of some flavoured binary alcohols at temperatures 298.15, 308.15 and 318.15 K

ABSTRACT

From the measured work of Ching-Ta and Chein-Hsiun Tu, we have presented the theoretical results of Surface tension and excess volume for three binary systems: namely 2-Propanol+Benzyl alcohol(1), 2-Propanol+2-Phenylethnol(2) and Benzyl alcohol+2-Phenylethanol(3) at temperatures 298.15, 308.15 and 318.15 K and atmospheric pressure over the concentration range 0.05–0.95. Theoretical results were computed from Flory model, Ramaswamy and Anbananthan (RA) model and model devised by Glinski, and studied the mixing properties and interactions of these liquids. Deviations in the surface tension (?σ) were evaluated and fitted to the Redlich–Kister polynomial equation to derive the binary coefficients and standard errors. Moreover, McAllister multi-body interaction model based on Eyring’s theory of absolute reaction rates has also been applied. For liquid mixtures, the free energy of activation is additive, based on the proportions of the different components of the mixture and interactions of like and unlike molecules. The behaviour of the liquids was studied and correlated with the molecular interactions from these liquid state models. Conclusively, these non-associated and associated models were compared and tested for different systems showing that the McAllister multi-body interaction model yields good results as compared to associated models, while Flory model shows more deviations.     

The boundary condition at the air–liquid interface and its effect on film drainage between colliding bubbles

The drainage of thin liquid films between colliding bubbles is strongly influenced by the boundary conditions at the air–liquid interface. Theoretically, the interface should not resist any tangential stress (fully mobile) in a clean water system, resulting in very fast film drainage and coalescence between bubbles within milliseconds. In reality, under most experimental and industrial conditions, the presence of impurities or surfactants can immobilize the interface and significantly hinder bubble coalescence by several orders of magnitude. In this opinion, we introduce the recent progress on understanding the boundary conditions at the air–water interface, and how they may affect the outcome of bubble collisions. The transition from mobile to immobile boundary conditions in the presence of contaminations is discussed. Despite the considerable recent progress, there are still experimental and theoretical challenges remaining on this topic, for example, finding the mechanism for hindered bubble coalescence by high salt concentrations.     

Unified molecular view of the air/water interface based on experimental and theoretical χ(2) spectra of an isotopically diluted water surface

The energetically unfavorable termination of the hydrogen-bonded network of water molecules at the air/water interface causes molecular rearrangement to minimize the free energy. The long-standing question is how water minimizes the surface free energy. The combination of advanced, surface-specific nonlinear spectroscopy and theoretical simulation provides new insights. The complex χ((2)) spectra of isotopically diluted water surfaces obtained by heterodyne-detected sum frequency generation spectroscopy and molecular dynamics simulation show excellent agreement, assuring the validity of the microscopic picture given in the simulation. The present study indicates that there is no ice-like structure at the surface--in other words, there is no increase of tetrahedrally coordinated structure compared to the bulk--but that there are water pairs interacting with a strong hydrogen bond at the outermost surface. Intuitively, this can be considered a consequence of the lack of a hydrogen bond toward the upper gas phase, enhancing the lateral interaction at the boundary. This study also confirms that the major source of the isotope effect on the water χ((2)) spectra is the intramolecular anharmonic coupling, i.e., Fermi resonance.     

Mutual influence of cetyltrimethylammonium bromide and Triton X-100 on their adsorption at the water–air interface

On the basis of surface tension values of the aqueous solution of cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) mixtures measured at 293 K as a function of CTAB or TX-100 concentration at constant TX-100 or CTAB concentration, respectively, the real surface area occupied by these surfactants at the water–air interface was established which is inaccessible in the literature. It appeared that at the concentration of the CTAB and TX-100 mixture in the bulk phase corresponding to the unsaturated monolayer at the water air-interface this area is the same as in the monolayer formed by the single surfactant at the same concentration as in the mixture. In the saturated mixed monolayer at this interface the area occupied by both surfactants is lower than that in the single surfactant monolayer corresponding to the same concentration in the aqueous solution. However, the decrease of the CTAB adsorption is lower than that of TX-100 and the total area occupied by the mixture of surfactants is also lower than that of the single one. The area of particular surfactants in the mixed saturated monolayer changes as a function of TX-100 and CTAB mixture concentration and at the concentrations close to CMC or higher the area occupied by both surfactants is the same. The changes of the composition of the mixed surface monolayer are connected with the synergetic effect in the reduction of the water surface tension by the adsorption of CTAB and TX-100 at the water–air interface. This effect was confirmed by the values of the standard Gibbs free energy of adsorption of both individual surfactants and their mixtures with different compositions in the bulk phase determined by using the Langmuir equation if RT instead of nRT was applied in this equation.     

The promotion effect of oxygen on the dissociative adsorption of water to uranium dioxide surface: a GGA + U study

Journal of Radioanalytical and Nuclear Chemistry - The promotion effect of O2 on the dissociative adsorption of H2O to UO2 surface is studied by first-principles method within...     

The effect of metal optical constants on far- and mid-infrared reflection—absorption

Although mid-infrared reflection—absorption spectroscopy is almost routine in some laboratories, the application of this technique to far-infrared spectroscopy is generally acknowledged as a difficult experiment at best. In this report the effect of increasing optical indices with wavelength for metals is demonstrated to be a root cause of this difficulty. When appropriate, iron is a reasonable substrate because of the comparatively small imaginary component of its refractive index in the far-infrared region. In addition, there is only a modest loss in spectral intensity of the spectrum for a film on iron relative to the use of the more noble metals as substrate.     

A CFD investigation of the effect of non-Newtonian behavior of Cu–water nanofluids on their heat transfer and flow friction characteristics

Journal of Thermal Analysis and Calorimetry - In the present study, a finite volume method is used to investigate heat transfer and flow friction behavior of non-Newtonian nanofluids. To study a...     

Liquid densities and excess molar volumes for water + diethylene glycolamine,and water,methanol, ethanol, 1-propanol + triethylene glycol binary systems at atmospheric pressure and temperatures in the range of 283.15–363.15 K

Liquid densities and excess molar volumes (V^E) are reported for the binary water+diethylene glycolamine, and water, methanol, ethanol, 1-propanol+triethylene glycol systems at atmospheric pressure and temperatures between 283.15 and 363.15 K in 10 K intervals. Negative V^E were found for all investigated systems. At given temperature, the most negative V^E is for the water+diethylene glycolamine system. For water containing systems, V^E increase with temperature while the inverse effect was observed for alcoholic systems, i.e. V^E became more negative with increasing temperature. For the triethylene glycol systems at constant temperature, absolute value of V^E decreases in the series: water>methanol>ethanol>1-propanol within the whole composition range. The experimental results have been correlated using the three parameter Redlich–Kister equation.     

Assessment of tritium distribution in rain,surface and drinking water in Portugal during 2006–2017 period

Journal of Radioanalytical and Nuclear Chemistry - Water samples from different origins (rain, surface and drinking) collected in Portugal during the years 2006 to 2017 were analyzed for the...     

The effect of coal particle aggregation on the sedimentation and rheology of coal—oil mixtures

The degree of coal particle aggregation in model oil suspension was assessed by particle size distribution using a sedimentation balance. Various statistical parameters were calculated for three suspensions each prepared with Sewell coal, model oil, and (1) calcium petroleum sulfonate (2) no additive and (3) an ethoxylated quartenary ammonium salt. These formulations represented suspensions which were (1) aggregatively stable (2) slightly aggregated and (3) highly aggregated, respectively.Batch settling tests were also conducted with the three formulations at coal concentrations of 10, 35 and 50%. These results indicated that the clarity of the supernatant, the initial settling velocity and the terminal sediment volume increased as the degree of aggregation increased. Rheological data indicated that the aggregatively stable suspensions were Newtonian but that pseudoplasticity and yield stresses were observed in the other formulations to an extent which increased as the degree of aggregation increased.     

Adsorption of Triton X-100 and cetyltrimethylammonium bromide mixture with ethanol at nylon-6–solution interface with regard to nylon-6 wettability: I. The effect of adsorption on critical surface tension of nylon-6 wetting

The contact angle measurements of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (TX-100) and cetyltrimethylammonium bromide (CTAB) mixture with ethanol on nylon-6 were made in the range of the total concentration of CTAB and TX-100 mixture from 1 × 10^?6 to 1 × 10^?3 M and ethanol from 0 to 17.13 M. In the CTAB and TX-100 mixture the mole fraction of TX-100 was equal to 0; 0.2; 0.4; 0.6; 0.8 and 1. On the basis of the obtained results, the critical surface tension of nylon-6 wetting was determined from the dependence of cosine of contact angle and the adhesion tension as a function of the surface tension of the solution. This tension was compared to the components and parameters of nylon-6 surface tension taken from literature and discussed in the light of the surface excess concentration of the surface active agents at the nylon-6–solution interface calculated from the Lucassen-Reynders equation and the Gibbs isotherm.     

Role of cationic moiety in phosphate fertilizers’ molecules on their solution behavior in terms of volumetric and acoustic parameters at different temperatures and atmospheric pressure

Ultrasonic parameters are very useful tools used to study the physic-chemical behavior and molecular interactions of various liquid mixtures. More than 50% problems of irrigated areas are associated with cultivated land and they frequently occur due to salinity. Application of fertilizers into agricultural land could be a remedy for soil salinity by providing essential nutrients to plants. In this research paper, ultrasonic and volumetric properties of phosphate based fertilizers of different molecular compositions at different temperatures have been studied. This is experimental based work; this knowledge can be employed in formulation of fertilizers according to the nature of their application which could enhance fertilizer’s activity either in terms of nutrients development or to control the salinity of soil. Results obtained from calculated ultrasonic and volumetric parameters indicated presence of strong interactions in aqueous fertilizer solutions which depends upon nature of molecules. Among presently studied phosphate fertilizers i.e. triple superphosphate, nitrophosphate and diammonium phosphate, maximum molecular interactions were observed in aqueous triple super phosphate solutions due to the presence of highly charged cationic specie i.e. calcium ions, which can also be used to control the salinity of soil using electrostatic interactions among saline salts and charged cationic species.     

Density and excess molar volumes of binary mixtures of sulfolane with methanol,n -propanol,n -butanol,and n -pentanol at 298.15–323.15 K and atmospheric pressure

Densities, ρ and excess molar volumes, V?^E of the binary mixtures of sulfolane, +methanol, +n-propanol,?+n-butanol, and +n-pentanol were measured at temperatures 298.15, 303.15, 308.15, 313.15, and 318.15?K, respectively, covering the whole composition range except methanol at 303.15–323.15?K. The V ^E for the systems were found to be negative and large in magnitude. The values of V ^E of the sulfolane, +n-butanol and sulfolane, +n-pentanol mixtures are being positive at lower and higher mole fractions of the alkanols (x ₂). The magnitudes of the V ^E values of the mixtures are in the order sulfolane?+?methanol?>?sulfolane?+?n-propanol?>?sulfolane?+?n-butanol?>?sulfolane?+?n-pentanol. The observed values of V ^E for the mixtures have been explained in terms of (i) effects due to the differences in chain length of the alcohols, (ii) dipole–dipole interactions between the polar molecules, and (iii) geometric effect due to the differences in molar volume of the component molecules. These are more noticeable in the case of lower alcohols. All these properties have been expressed satisfactorily by appropriate polynomials.     

A cosolvent pretreatment: effect of solvent–water on enzymatic hydrolysis of glucan,lignin structure,and dynamics

Cellulose - In this study, a biomass pretreatment strategy with a recyclable cosolvent (toluene sulfonic acid/ethanol) was developed. The low boiling point solvent (78.15 °C),...     

Well-defined critical association concentration and rapid adsorption at the air/water interface of a short amphiphilic polymer, amphipol A8-35: a study by Förster resonance energy transfer and dynamic surface tension measurements

Amphipols (APols) are short amphiphilic polymers designed to handle membrane proteins (MPs) in aqueous solutions as an alternative to small surfactants (detergents). APols adsorb onto the transmembrane, hydrophobic surface of MPs, forming small, water-soluble complexes, in which the protein is biochemically stabilized. At variance with MP/detergent complexes, MP/APol ones remain stable even at extreme dilutions. Pure APol solutions self-associate into well-defined micelle-like globules comprising a few APol molecules, a rather unusual behavior for amphiphilic polymers, which typically form ill-defined assemblies. The best characterized APol to date, A8-35, is a random copolymer of acrylic acid, isopropylacrylamide, and octylacrylamide. In the present work, the concentration threshold for self-association of A8-35 in salty buffer (NaCl 100 mM, Tris/HCl 20 mM, pH 8.0) has been studied by F?rster resonance energy transfer (FRET) measurements and tensiometry. In a 1:1 mol/mol mixture of APols grafted with either rhodamine or 7-nitro-1,2,3-benzoxadiazole, the FRET signal as a function of A8-35 concentration is essentially zero below a threshold concentration of 0.002 g·L(-1) and increases linearly with concentration above this threshold. This indicates that assembly takes place in a narrow concentration interval around 0.002 g·L(-1). Surface tension measurements decreases regularly with concentration until a threshold of ca. 0.004 g·L(-1), beyond which it reaches a plateau at ca. 30 mN·m(-1). Within experimental uncertainties, the two techniques thus yield a comparable estimate of the critical self-assembly concentration. The kinetics of variation of the surface tension was analyzed by dynamic surface tension measurements in the time window 10 ms-100 s. The rate of surface tension decrease was similar in solutions of A8-35 and of the anionic surfactant sodium dodecylsulfate when both compounds were at a similar molar concentration of n-alkyl moieties. Overall, the solution properties of APol "micelles" (in salty buffer) appear surprisingly similar to those of the micelles formed by small, nonpolymeric surfactants, a feature that was not anticipated owing to the polymeric and polydisperse nature of A8-35. The key to the remarkable stability to dilution of A8-35 globules, likely to include also that of MP/APol complexes, lies accordingly in the low value of the critical self-association concentration as compared to that of small amphiphilic analogues.