Further studies on the effect of degassing on the dispersion and stability of surfactant-free emulsions

Recently reported results indicate that the formation of surfactant-free, oil-in-water emulsions can be significantly enhanced by the almost complete removal of dissolved gases and that the reintroduction of dissolved gases does not immediately destabilize the already-formed emulsions. These initial experiments have been repeated and extended to include a wider range of organic liquids and the application of light scattering to determine droplet size and distribution. The earlier observations have been confirmed. In addition, a systematic trend was found between the solubility of the oil in water and the stability (lifetime) of the degassed oil droplets in water. The lower the solubility, the more stable the emulsion, and for oils that are sparingly soluble in water such as squalane, the small droplets remain stable for several weeks, with buoyancy separation being the main cause of instability of the large droplets with time. The addition of electrolytes, up to molar concentrations, substantially reduces the enhancement of the dispersions on degassing but appears to have little effect on the stability of the already-formed emulsions. The reduction of pH to about 2 significantly reduces both the enhancement of the dispersions on degassing and the stability of the already-formed emulsions. In contrast, the increase of pH to about 11 hardly affects the enhancement of the dispersions on degassing or the stability of the already-formed emulsions. We have confirmed the importance of dissolved gas and its association with the electrostatic effects, but we still cannot provide a complete explanation for the effect of degassing on the hydrophobic dispersions.     

The hydrophobicity of non-aqueous liquids and their dispersion in water under degassed conditions

Several recent studies have shown that many oils, such as hydrocarbons, fluorocarbons, silicone and natural oils, are more readily dispersed as fine (micron-sized) droplets in water when the mixtures are almost completely degassed. These observations have not yet been fully explained and so this paper examines the nature of hydrophobicity of a wide range of oils and considers both the cavitation process and the surface charging expected during the separation of hydrophobic materials in water. Cavitation inside porous hydrophobic solids immersed in water is also considered. We also introduce a quick, easy and alternative method to freeze–thaw degassing, by which enhanced dispersions can be formed, which gives further support to the central role of degassing.     

Influence of degree of gas saturation on multibubble sonoluminescence intensity

The influence of the degree of saturation (DOS) of a gas in a solution on the intensity of multibubble sonoluminescence (MBSL) excited by ultrasound with a frequency of 261 kHz is investigated at various ultrasonic powers and with different concentrations of ethanol, which is added as a volatile solute. At relatively low powers and a high DOS, low ethanol concentrations give higher sonoluminescence (SL) intensities than those obtained with pure water. This intensity enhancement decreases as sonication proceeds because the SL intensity for pure water increases with time, whereas it remains almost constant or decreases slightly in solutions containing ethanol. At relatively low powers, a partially degassed solution has a higher SL intensity than a solution with a high DOS for both pure water and solutions containing ethanol. The reason why the DOS decreases more when ethanol is added is considered mainly to be the accumulation of hydrocarbon products and the promotion of rectified diffusion. Adding an alcohol to a solution enhances ultrasonic degassing.     

Membranes of vertically aligned superlong carbon nanotubes

In the present work, we have developed a simple but effective method to prepare superlong vertically aligned carbon nanotubes (SLVA-CNT) and epoxy composite membranes, and we have demonstrated that various liquids, including water, hexane, and dodecane, can effectively pass through the SLVA-CNT membranes. These results were confirmed by molecular dynamics simulations. While the mechanical densification was used to further enhance the flow transport through the SLVA-CNT membranes, we developed in this study a magnetic-nanoparticle switching system to turn on and off the flow through the nanotube membrane by simply applying an alternating voltage. The methodologies developed in this study should have a significant implication to the development of various smart membranes for advanced intelligent systems.     

THE EFFECT OF pH ON THE AEROBIC and ANAEROBIC PHOTOLYSIS OF TRYPTOPHAN AND SOME TRYPTOPHAN-CONTAINING DIPEPTIDES

Abstract— Rates of photolysis, quantum yields of fluorescence, and fluorescence emission maxima for the dipeptides glycyltryptophan (Gly-Trp) and tryptophylglycine (Trp-Gly) and for free tryptophan (Trp) were determined under both degassed and aerated conditions in the pH range 4.5-10.0. The photolyses were performed at 25°C using 290 nm radiation from a 1000 W xenon lamp. Photolysis rates were determined by monitoring tryptophan fluorescence loss with time. It was found that Trp-Gly and free Trp showed similar behavior in that their fluorescence quantum yields and photolysis rates increased significantly above neutral pH. In contrast, the Gly-Trp fluorescence yield was smaller than that of Trp or Trp-Gly, showing no significant increase at high pH and the photolysis rate for Gly-Trp decreased with increasing pH. In comparing aerated to degassed samples, it was found that degassing had a far greater effect on the photolysis rates of Trp and Trp-Gly than on the photolysis rate of Gly-Trp especially at higher pH. But, degassing did not change the relative fluorescence quantum yields or fluorescence emission maxima of any of the three compounds. Possible mechanisms for photolysis under various experimental conditions were examined in light of the data.     

Measurements and modeling of quaternary (liquid + liquid) equilibria for mixtures of (methanol or ethanol + water + toluene + n-dodecane)

The extraction of aromatic compound toluene from alkane, dodecane, by mixed solvents (water + methanol), (water + ethanol) and (methanol + ethanol) have been studied by (liquid + liquid) equilibrium (LLE) measurements at three temperatures (298.15, 303.15, and 313.15) K and ambient pressure. The compositions of liquid phases at equilibrium were determined by gas liquid chromatography.The experimental tie-line data for three quaternary mixtures of {(water + methanol) + toluene + dodecane}, {(water + ethanol) + toluene + dodecane}, and {(methanol + ethanol) + toluene + dodecane} are presented. The experimental quaternary LLE data have been satisfactorily correlated by using the UNIQUAC and NRTL activity coefficient models. The parameters of the models have been evaluated and presented. The tie-line data of the studied quaternary mixtures also were correlated using the Hand method. The partition coefficients and the selectivity factor of solvent are calculated and compared for the three mixed solvents.The comparisons indicate that the selectivity factor for mixed solvent (methanol + ethanol) is higher than the other two mixed solvents at the three studied temperatures. However, considering the temperature variations of partition coefficients of toluene in two liquid phases at equilibrium, an optimum temperature may be obtained for an efficient extraction of toluene from dodecane by the mixed solvents.     

SET‐LRP of acrylates in air

Single Electron Transfer‐Living Radical Polymerization (SET‐LRP) represents a robust and versatile method for the rapid synthesis of macromolecules with well defined topology. In SET‐LRP, certain combinations of solvents and ligands facilitate the disproportionation of in situ generated Cu(I) species into “nascent” Cu(0) and Cu(II) species. A combination of heterogeneous and “nascent” Cu(0) activation yields polymers with very high chain end functionality. Under suitable conditions the tolerance toward oxygen must be increased since Cu(0), the activator in SET‐LRP, acts as an oxygen scavenger in all inert gas purification systems. Here we demonstrate that SET‐LRP of methyl acrylate can be conducted in the presence of air. The addition of a small amount of reducing agent hydrazine hydrate to the reaction mixture reduces Cu₂O generated by the oxidation of Cu(0) with air, regenerating Cu(0) and allowing for the synthesis of polymers with predictable molecular weight and perfect retention of chain end functionality. The kinetics plots obtained under these conditions were identical to these generated by degassed samples. High conversions were achieved within a very short reaction time. In these SET‐LRP experiments, the reagents were not deoxygenated or subjected to standard degassing procedures such as freeze‐pump‐thaw or nitrogen sparging. This simple SET‐LRP procedure provides an efficient and economical approach to the synthesis of functional macromolecules. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1190–1196, 2010     

A 1H magnetic resonance imaging study of porosity in polyurethane foams

¹H magnetic resonance imaging (MRI) is used to study the distribution of water in polyurethane foams. Flexible open-celled foams are easily distinguished from the closed-cell foams as the latter does not absorb any detectable amounts of water. Flexible foams degassed in vacuo revealed no structural detail due to the resolution limitation of approximately 100 μm. Incompletely degassed foams revealed considerable areas of trapped gas which were recorded as a function of distance beneath the water. Samples injected with water indicated that a tortuous flow pathway is taken due to the presence of cell windows. Samples with lower porosity had a higher resistance to flow.     

Morphology study of Nafion membranes prepared by solutions casting

The structures of Nafion membranes prepared by solutions casting from low aliphatic alcohols/water mixture solvents and N,N′‐dimethyl formamide (DMF) solvent were investigated using differential scanning calorimeter and small angle X‐ray scattering. The aggregation behavior of Nafion molecules in the casting solutions was also investigated using dynamic light scattering. We show that the morphology of membranes was strongly influenced by the conformations of Nafion molecules in the solutions. In aliphatic alcohol/water mixture solvents, which have a worse compatibility with Nafion backbones, the Nafion molecules aggregate and form fringed rod‐like structures. These primary rod‐like structures then aggregate again through fringed side chains to form secondary ionic aggregations. In DMF solvent, owing to its better compatibility with Nafion backbones, less Nafion molecules aggregate. The high degree of Nafion molecular aggregations in aliphatic alcohol/water mixture solvents leads to a high degree of hydrophobic and hydrophilic phase separation for membranes prepared by casting from Nafion/aliphatic alcohol/water solutions. However, the lower degree of molecular aggregations in DMF solvent results in a lower degree of hydrophobic and hydrophilic phase separation for membranes prepared by casting from Nafion/DMF solution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3044–3057, 2005     

Phase behavior and rheology of oil-swollen micellar cubic phase and gel emulsions in nonionic surfactant systems

We have studied the phase behavior and rheological property of the cubic phase and related gel emulsions in water/nonionic/dodecane systems. In the phase behavior study, it is pointed out that the formation of the discontinuous cubic phase (I₁) is not common in all nonionic surfactant systems; however, a cubic phase (I₁) with oil-swollen micelles or a cubic phase microemulsion is found in the water/C₁₆EO₆/dodecane system, which can solubilize large amount of oil. It was also observed that water/C₁₆EO₆/dodecane system forms stable gel emulsion. In the rheological study we have found an anomalous behavior of the I₁ phase in the water/C₁₂EO₆/dodecane and the water/C₁₆EO₆/dodecane systems. In the water/C₁₂EO₆/dodecane system, the viscoelastic nature of the I₁ phase has been observed, which is shifted to the elastic nature with the addition of dodecane, whereas, highly elastic nature was observed in the water/C₁₆EO₆/dodecane system. In both the cases shear-thinning behavior were seen. The elastic modulus, G′ and complex viscosity, |η1| of the I₁ phase increase with the dodecane concentration in the water/C₁₂EO₆/dodecane system, whereas, decreasing trend have been observed in the water/C₁₆EO₆/dodecane system. This anomalous behavior is suggested due to the nonspherical shape of micelles or polydispersity of the micelles in the water/C₁₆EO₆/dodecane system. The rheological behavior of the O/I₁ gel emulsion was also studied in both the systems.     

Extending the applicability of pressurized hot water extraction to compounds exhibiting limited water solubility by pH control: curcumin from the turmeric rhizome

Pressurized hot water extraction (PHWE, also known as subcritical water extraction) is commonly considered to be an environmentally friendly extraction technique that could potentially replace traditional methods that use organic solvents. Unfortunately, the applicability of this technique is often limited by the very low water solubility of the target compounds, even at high temperatures. In this paper, the scope for broadening the applicability of PHWE by adjusting the pH of the water used in the extraction is demonstrated in the extraction of curcumin (which exhibits very limited water solubility) from untreated turmeric (Curcuma longa L.) rhizomes. Although poor extraction yields were obtained, even at high temperatures when using degassed water or neutral phosphate buffer as the extraction medium, yields exceeding those obtained by Soxhlet extraction were achieved using highly acidic pH buffers due to curcumin protonation. The influence of the temperature, pH, and buffer concentration on the extraction yield were investigated in detail by means of a series of designed experiments. Optimized conditions for the extraction of curcumin from turmeric by PHWE were estimated at 197 °C using 62 g/L buffer concentration at pH 1.6. The relationships between these variables were subjected to statistical analysis using response surface methodology.     

A novel synthesis method for cyclodextrins from maltose in water-organic solvent systems

A novel enzymatic synthesis method of cyclodextrin (CD) from low-mol-wt maltose using cyclomaltodextrin glucanotransferase (CGTase) fromBacillus macerans has been developed in various water-organic solvent systems. A Β-CD was synthesized in a two-phase system consisting of water and cyclohexane. However, no CDs could be synthesized in an aqueous buffer solution. A maximal yield of Β- CD has been obtained at a cyclohexane content volume of 44%. This synthesis has been obtained only at low temperatures, i.e., 7‡C, and did not take place at 50‡C. In addition, various organic solvents have been used for the enzymatic synthesis of CD from maltose. Consequently, Β-CD could be synthesized in various water-organic solvent systems, e.g., cyclohexane, benzene, xylene, and chloroform, but no enzymatic reaction occurred using aliphaticn-hydrocarbon solvents such as hexane, dodecane, and hexadecane. Furthermore, α- and Β- CD could be synthesized in water mixture solutions using organic solvents having an alcoholic group (e.g., ethanol, propanol, butanol, and pentanol) in a wide range of the reaction temperatures, typically 7–50‡C. In this temperature range, α- and Β-CD were also formed and the maximal yield from maltose to Β-CD of approx 13% was reached in 60 h.     

Density Functional Theory Study of Solvent Effects on the Structure and Vibrational Frequencies of Tetranitrotetraazabicyclooctane “bicyclo‐HMX”

Density Functional Theory (DFT) calculations have been performed on the high explosive compound tetranitrotetraazabicyclooctane (bicyclo‐HMX) in gas phase employing the self‐consistent field (SCF) theory and in different solvents, i.e. cyclohexane, dichloroethane, ethylalcohol, acetonitrile, and water, utilizing the self‐consistent reaction field (SCRF) theory at a B3LYP/6–31 1G** level of theory. Reasonable agreement has been found between the computed and the available experimental data. The effects of different solvents on the geometry, electronic structure, and vibrational frequencies are discussed. Various solvents under consideration are found to have similar effects on the above properties. But some properties change regularly with the increasing polarity of the solvents, and the stronger the solvent polarity is, the larger the change is. In addition, based on the vibrational analysis, standard thermodynamic properties of bicyclo‐HMX in gas phase are also computed by using the statistical thermodynamic principle.     

Detection of novel gaseous states at the highly oriented pyrolytic graphite-water interface

We report a novel form of the gaseous state at the interface of water and highly oriented pyrolytic graphite (HOPG) that is induced by local supersaturation of gas. Such local supersaturation of gas next to the HOPG substrate can be achieved by (1) displacing an organic liquid with a gentle flow of water, (2) displacing cold water (approximately 0 degrees C) with a gentle flow of warm water (approximately 40 degrees C), or (3) preheating the HOPG substrate to approximately 80 degrees C before exposing it to water at room temperature. In addition to the spherical-cap-shaped nanobubbles reported by many researchers, flat (quasi-two-dimensional, pancake-like) gas layers and nanobubble-flat gas layer composites (spherical-cap-shaped nanobubbles sitting on top of the quasi-two-dimensional gas layers) were detected. These entities disappeared after the system was subjected to a moderate level of degassing (approximately 0.1 atm for 1.5 h), and they did not form when the liquids involved in the aforementioned displacing procedure (to induce local supersaturation of gas) had been predegassed (to approximately 0.1 atm). The stability and some physical properties of these newly found gaseous states are examined.     

不同溶剂对聚醚砜酮基炭膜结构及气体分离性能的影响

为考察不同溶剂对聚醚砜酮(PPESK)炭膜结构和性能的影响,以PPESK为前驱体,分别以NMP,CHCl3,C2H2Cl4,DMAc为溶剂制备气体分离炭膜。并采用红外光谱、热重分析、X射线衍射和气体渗透等测试手段对所制膜的化学结构、炭膜的微结构和气体的分离性能进行了表征。结果表明,溶剂的溶度参数、沸点、挥发性以及原膜中溶剂的含量等导致所制备聚合物膜形成不同的化学结构,改变它在预氧化和炭化过程的结构变化规律,使形成炭膜表现出不同的炭结构、孔隙结构和表观柔韧性,最终影响炭膜的气体渗透性和分离选择性。     

Morphology of microporous poly(vinylidene fluoride) membranes studied by gas permeation and scanning electron microscopy

Microporous poly(vinylidene fluoride) (PVDF) membranes with asymmetric pore structure were prepared by a wet phase inversion process. The polymer was precipitated from a casting solution when immersed in a cold water (gelation) bath. The casting solution was, in most cases, composed of polymer, solvent, and nonsolvent. In this solvent-nonsolvent system, the solvents used were triethylphosphate (TEP) and dimethylsulfoxide (DMSO), and the nonsolvents used were glycerol and ethanol. Mean pore sizes and effective porosity of the microporous membranes were calculated using the gas permeation method. They were studied as a function of evaporation time of wet nascent film, polymer molecular weight, concentration of polymer, and concentration of nonsolvent. The morphology of the membranes was examined by scanning electron microscopy (SEM).     

Effects of pulsed low-frequency electromagnetic fields on water characterized by light scattering techniques: role of bubbles

Well-characterized purified water was exposed for 6 h to pulsed low-frequency weak electromagnetic fields. After various time periods, nondegassed and degassed water samples were analyzed by static light scattering. Just after electromagnetic exposure (day 0), a reduction of over 20% in the maximum light scattering intensity at 488 nm wavelength in both nondegassed and degassed samples was observed. By contrast, on day 12 the difference was observed only in nondegassed water samples. The latter effect was attributed to the different geometries of the containers combined with the basic origin of the whole phenomenon due to gas bubbles present in water. By the use of dynamic light scattering, the bubble mean diameter was estimated to be around 300 nm. Our results suggest that the electromagnetic exposure acts on gas nanobubbles present in water and emphasizes the role of the gas/liquid interface. The possibility that exposure to electromagnetic fields disturbs the ionic double layer that contributes to bubble stabilization in water is discussed.     

Synthesis and optical properties of (a)chiral terpyridine-ruthenium complexes

Chiral terpyridine ligands have been synthesized and characterized. By applying Ru(III)/Ru(II) chemistry, symmetrical as well as asymmetrical bis-terpyridine ruthenium(II) complexes were obtained. These materials were fully characterized and their optical properties investigated. While the chiral metal complexes revealed no Cotton effect in good solvents such as chloroform, CD-measurements in dodecane showed an effect in both ligand and MLCT regions, suggesting chirality transfer from the lateral alkyl chains to the complex core. This behavior points to the formation of supramolecular aggregates in dodecane. Furthermore, the analogous achiral ligand and its corresponding ruthenium(II) complexes were prepared.     

Effects of degassing and ionic strength on AFM force measurements in octadecyltrimethylammonium chloride solutions

Sakamoto et al. (Langmuir 2002, 18, 5713) conducted AFM force measurements between silica sphere and fused-silica plate in aqueous octadecyltrimethylammonium chloride (C18TACl) solutions and concluded that long-range attractive force is not observed in carefully degassed solutions. In the present work, AFM force measurements were conducted by following the procedures described by Sakamoto et al. The results showed the presence of an attractive force that was much stronger than the van der Waals force both in air-saturated and degassed solutions. The force was most attractive at 5 x 10(-6) M C18TACl, where contact angle was maximum. At this concentration, which is close to the charge compensation point (ccp) of the glass sphere, the long-range decay lengths (D) were 34 and 38 nm in air-saturated and degassed solutions, respectively. At 10(-5) M, the decay length decreased from 30 to 4 nm upon degassing. This decrease in decay length can be explained by a pH increase (from 5.7 to 6.6), which in turn causes additional surfactant molecules to adsorb on the surface with inverse orientation. The attractive force was screened by an added electrolyte (NaCl), indicating that the attractive force may be of electrostatic origin. Therefore, the very long decay lengths observed in the absence of electrolyte may be ascribed to the fact that the ccp occurs at a very low surfactant concentration.     

Oxygenation by a superhydrophobic slip G/L contactor

The compelling need for an efficient supply of gases into liquids or degassing of fluids within confined microchannels triggered our study on membrane assisted microchemical systems. Porous hydrophobic flat/micro-structured polyvinylidene fluoride (PVDF) membranes were fabricated and integrated in a glass G/L contacting microfluidic device with the aid of optical adhesives. The oxygen transport in microchannels, driven by convection and diffusion, was investigated both experimentally and numerically. The effects of intrinsic membrane morphology on the G/L contacting performance of the resultant membranes were studied. The experimental performance of the flat membranes are shown to obey the simulation results with the assumptions of negligible gas phase and membrane mass transfer limitations. Micro-structured membranes revealed apparent slippage and enhanced mass transport rates, and exceeded the experimental performance of the flat membranes.