Liquid-liquid interfacial tension of equilibrated mixtures of ionic liquids and hydrocarbons

Ionic liquids are possible alternative solvents for the separation of aromatic and aliphatic hydrocarbons by liquid-liquid extrac- tion. Interfacial tension is an important property to consider in the design of liquid-liquid extraction processes. In this work, the liquid-liquid interfacial tension and the mutual solubility at 25 °C have been measured for a series of biphasic, equilibrated mixtures of an ionic liquid and a hydrocarbon. In particular, the ionic liquids 1-alkyl-3-methylimidazolium bis(trifluorome- thanesulfonyl)imide (with the alkyl substituent being ethyl, hexyl or decyl), 1-ethyl-3-methylimidazolium ethylsulfate, and 1-ethyl-3-methylimidazolium methanesulfonate have been selected, as well as the hydrocarbons benzene, hexane, ethylben- zene, and octane. The selected sets of ionic liquids and hydrocarbons allow the analysis of the influence of a series of effects on the interfacial tension. For example, the interfacial tension decreases with an increase in the length of the alkyl substituent chain of the cation or with an increase of the degree of charge delocalisation in the anion of the ionic liquid. Also, the interfa- cial tension with the aromatic hydrocarbons is markedly lower than that with the aliphatic hydrocarbons. A smaller effect is caused by variation of the size of the hydrocarbon. Some of the observed trends can be explained from the mutual solubility of the hydrocarbon and the ionic liquid.     

Viscoelastic properties and interfacial tension of polystyrene–polyethylene blends

The linear viscoelastic properties of polystyrene polyethylene (PS/PE) blends have been investigated in the molten state. For concentrations of the dispersed phase equal to 30 vol %, the blends exhibited a droplet‐matrix morphology with a volume‐average diameter of 5.5 μm for a 70/30 PS/PE blend at 200 °C and 14.7 μm for a 30/70 PS/PE blend at 230 °C. Enhanced elasticity (G′) for both blends, in the terminal zone, compared to the modulus of the matrix (PS and PE, respectively) was observed. This is related to the deformation of the droplets in the matrix phase and hence to the interfacial forces between the blend components. The results for these uncompatibilized blends are shown to be in agreement with the predictions of the emulsion model of Palierne. These predictions were used to obtain the interfacial tension between PS and PE, which was found to be between 2 and 5 mN/m at 200 °C and 4 ± 1 mN/m at 230 °C. Independent interfacial tension measurements using the breaking‐thread method resulted in a value of 4.7 mN/m and 4.1 mN/m at 200 °C and 230 °C for the respective blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1359–1368, 2000     

Phase separation in mixtures of poly(ethylene glycol monomethylether) and poly(propylene glycol) oligomers

Time-resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two-phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time-evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensity I_m and the corresponding peak wavenumber q_m was found to follow the power-law {I_m(t)? t^α, q_m(t)? t^-β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self-similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted for off-critical mixtures.     

The interfacial tension of poly(ethylene oxide) and poly(propylene oxide) oligomers

Summary The interfacial tensions of a series of poly(ethylene oxides) (PEO) and poly(propylene oxides) (PPO) have been measured using a pendant drop technique. A drop of PEO was formed under the PPO, in a thermostatted cell usually at 73 °C, and it was photographed using parallel monochromatic light from a laser.The interfacial tensions were measured for a series of polymers of different molecular weights and were found to increase with increasing PPO molecular weight but to decrease slightly with increasing PEO molecular weight. The dependence on PPO molecular weight is explained as due to the adsorption of hydroxy end groups of the PPO at the PEO interface. When these end groups were "replaced by methoxy groups, the adsorption no longer took place and the interfacial tension increased.

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Zusammenfassung Die Grenzflächenspannungen einer Reihe von Polyäthylenoxyden (PEO) und Polypropylenoxyden (PPO) wurden mittels der Methode des hängenden Tropfens gemessen. Ein Tropfen aus PEO wurde erzeugt unter PPO in einer temperierten Zelle bei gewöhnlich 73 ° C und wurde in parallelem monochromatischem Licht eines Lasers photographiert.Die Grenzflächenspannungen wurden für eine Reihe von Polymeren mit unterschiedlichem Molekulargewicht gemessen und nahmen zu mit steigendem PPO-Molekulargewicht, nahmen aber leicht ab mit zunehmendem PEO Molekulargewicht. Die Abhängigkeit vom PPO Molekulargewicht wird erklärt als Effekt der Adsorption von Hydroxyl-Endgruppen des PPO an der PEO Grenzfläche. Ersetzt man diese Endgruppen durch Methoxyl-Gruppen, beobachtet man keine Adsorption und die Grenzflächenspannung nimmt zu.

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With 2 figures and 4 tables     

Conductance behaviour of HCl in water-ethylene glycol, water-diethylene glycol and ethylene glycol-diethylene glycol mixtures

The conductance behaviour of HCl in water-ethylene glycol, water-diethylene glycol and ethylene glycol-diethylene glycol mixtures was investigated in the complete range of solvent compositions of 25°C by applying the three-parameter conductance equation. No appreciable association of the acid was observed in any of the mixed solvents. The large decrease ofΛ ₀ andΛ ₀ η ₀ of the acid in the early and end composition region of the mixed solvents has been attributed to the drastic structural changes brought about by the addition of the organic component in the aqueous solvent mixtures and by the addition of diethylene glycol in the case of ethylene glycol-diethylene glycol mixtures.     

Simultaneous study of interfacial tension,surface tension,and viscosity of few surfactant solutions with survismeter

Surfaces and interfaces are receptive valuable significant property of chemical molecules due to their potential to develop several phenomena in a self‐controlled mechanism. Science of surfaces is vast and is being used industrially since time immemorial. Their accurate and simultaneous estimation is necessary; therefore, the survismeter was used for measuring them along with viscosity. Individually tensiometers, X‐ray reflective microscope, and viscometers are used for surface tension, interfacial tension, and viscosity, respectively. These devices are sophisticated, expensive, and individually consume much time and resources with poor reproducibility in measurements. Survismeter is an alternative device for similar measurements together with higher accuracies and reproducibility. It works on a principle of capillary flow and pressure gradient (PG) inside liquid‐holding and air‐filled bulbs. Several liquids have been used for study with ± 0.01 mN/m, ± 0.01 mN/m and ± 1 × 10^?5 N s/m² accuracies in respective data. Copyright © 2008 John Wiley & Sons, Ltd.     

Synergistic effect of mixed anionic and cationic surfactant systems on the interfacial tension of crude oil-water and enhanced oil recovery

Surfactant based enhanced oil recovery (EOR) is an interesting area of research for several petroleum researchers. In the present work, individual and mixed systems of anionic and cationic surfactants consisting of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) in different molar ratios were tested for their synergistic effect on the crude oil-water interfacial tension (IFT) and enhanced oil recovery performance. The combination of these two surfactant systems showed a higher surface activity as compared to individual surfactants. The effect of mixed surfactant systems on the IFT and critical micellar concentration (CMC) is strongly depends on molar ratios of the two surfactant. Much lower CMC values were observed in case of mixed surfactant systems prepared at different molar ratios as compared to individual surfactant systems. The lowest CMC value was found when the molar concentration of SDS was higher than the CTAB. When the individual and mixed surfacant systems were tested for EOR performance through flooding experiments, higher ultimate oil recovery was obtained from mixed surfactant flooding compared to individual surfactants. Combination of SDS and CTAB or probably other anionic-cationic surfactants show synergism with substantial ability to reduce crude oil water IFT and can be a promising EOR method.     

Liquid properties of oligomers. Comparison of relaxational properties of propylene glycol oligomers with those of ethylene glycol oligomers

Liquid properties such as dielectric relaxation and viscous flow of the two structurally homologous propylene glycol oligomers HO(CH(CH₃)CH₂O)_nH (n=1, 2, 3, 4, 5 and 34) and ethylene glycol oligomers HO(C₂H₄O)_nH (n=1, 2, 3, 4, 5 and 6) are studied in pure liquid state to clarify the degree of polymerization dependences of chain molecules on their liquid properties. These oligomers are, at room temperature, viscous liquid which shows dielectric relaxations in the frequency range from 10 Hz to 3 MHz. Propylene glycol oligomers (n=from 1 to 5) show the Davidson-Cole-type relaxations, but the higher glycol (n=34) shows superposition of the two different relaxations, i. e., small Debye-type relaxation in the lower-frequency region and large principal Havriliak-Negami-type relaxation in the higher-frequency region. Relaxation times vs. degree of polymerization do not increase linearly, but vary in zigzag lines. Above all, the dimers (dipropylene glycol and diethylene glycol) show longer relaxation times than the other glycols. This dielectric result does not agree with the degree of polymerization dependence of viscous flow.     

The influence of partial emulsification on coalescence suppression and interfacial tension reduction in PP/PET blends

This study examines how the relative role of coalescence suppression and interfacial tension reduction influence the particle size at various levels of in situ compatibilization. The polymers studied are polyethylene terephthalate (PET) as matrix and a polypropylene (PP) as dispersed phase compatibilized by a triblock copolymer of poly(styrene–hydrogenated butadiene–styrene) (SEBS) grafted with maleic anhydride. The interfacial tension was studied by the breaking‐thread method, and it was used along with the morphology to characterize the emulsification efficacy of the copolymers. By modifying the concentration of MA grafted on the SEBS, different levels of emulsification of the blends were obtained. A comparison of 1/99 and 10/90 PP/PET blends compatibilized by SEBS‐g‐MA allows one to distinguish the relative role of interfacial tension and coalescence suppression in diminishing particle size. It is shown that varying degrees of residual coalescence remain, depending on the level of %MA in the copolymer. A detailed study of the 2%MA system below interfacial saturation was carried out to shed further light on the dependence of coalescence suppression on emulsification level and interfacial coverage. After separating out the contribution of interfacial tension on particle size reduction, it is shown that coalescence suppression for this system increases gradually with areal density of modifier at the interface right up to the region of interfacial saturation. Finally, the interfacial and morphological data were used to test the ability of the Lee and Park model to describe coalescence in polymer blends. Reasonable agreement was found between the parameter c₁, describing the coalescence in that model, and the trends related to residual coalescence from this study. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 939–951, 1999     

Correlation between topological features and surface tension of binary liquid mixtures

Summary The excess surface tension of a large number of binary liquid mixtures has been correlated with their topological features quantified in terms of the molecular connectivity indices. The agreement between the calculated and experimental ^E values is reasonably well for all the mixtures. A simple correlation has also been proposed between ^E and molar excess volume (V ^E ) of a binary mixture. The correlation is quite useful in correlating ^E data even for the mixtures where either one or both the components are associated in the pure state and/or there is interaction between them.

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Korrelation zwischen topologischen Gegebenheiten und Oberflächenspannung von binären flüssigen Mischungen

Zusammenfassung Die Exzeß-Oberflächenspannungen einer großen Anzahl von binären flüssigen Mischungen wurden mit der Topologie ihrer Komponenten in Form der molekularen Konnektivitätsindices korreliert. Die Übereinstimmung zwischen den ^E -Werten ist für alle Mischungen relativ gut. Es wurde ebenfalls eine einfache Korrelation zwischen ^E und den molaren Exzeß-Volumina (V ^E ) der binären Mischungen vorgeschlagen. Diese Korrelierung ist nützlich, um die ^E -Werte sogar dann für die Korrelation von Mischungen verwenden zu können, wenn entweder eine oder beide Komponenten im Reinzustand assoziiert sind und/oder eine Wechselwirkung zwischen ihnen besteht.

     

Measurement of the interfacial tension between polyethersulfone and a thermotropic liquid-crystalline copolyester

Due to the increasing interest in forming blends of liquid-crystalline polymers with conventional thermoplastics, it becomes important to determine the interfacial tension between two such polymers. A method for evaluating the interfacial tension between a thermotropic copolyester based on hydroxybenzoic and hydroxynaphthoic acid residues, and polyethersulfone is presented, based on the Fort and Patterson method. It is found that the value of the interfacial tension in the melt is much higher than is the case between conventional polymer pairs. It is suggested that this high value reflects an entropic effect due to the strong exclusion of the flexible coil polymer from the nematic melt. © 1993 John Wiley & Sons, Inc.     

Rheo-optical determination of the interfacial tension in a dispersed blend

In this work, we present two novel methods to determine the interfacial tension of a disperse polymer blend through rheo-optical measurements of flow-induced single drop distortions. A counter-rotating shearing device with transparent plates is used to measure drop distortions. The cell geometry allows for a top view of the deforming drop, i.e., along the velocity gradient direction. Such a view is the only possible option for all currently available commercial rheo-optical instruments. Two different quantities are monitored, namely, the drop axis along the vorticity direction, and the rotation period of the drop surface. We use drops of a polyacrilamide aqueous solution (a shear thinning liquid) immersed in a polyisobutene matrix. Experimental results are interpreted in terms of theories for Newtonian liquids, where the relevant parameter is the Capillary number. If an appropriate viscosity ratio is chosen, that accounts for the shear thinning behaviour of the drop phase, good agreement is found between measurements and theoretical predictions. As a result, a robust estimate of the blend interfacial tension, that makes use only of the information acquired from top view experiments, is obtained.     

Interfacial tension coefficient from the retraction of ellipsoidal drops

A new method for the determination of the interfacial tension coefficient between two immiscible fluids is proposed. The method is particularly useful for the binary polymer blends. The deformed drop retraction method, DDRM, makes it possible to determine the dynamic interfacial tension coefficient, ν, from the time evolution of a distorted fluid drop toward its equilibrium form. Analysis of this interfacial tension-driven process led to a theoretical relation between the shape retraction rate and the system's geometrical and rheological characteristics. Measurements of either low viscosity model systems or high viscosity industrial polymer mixtures led to a good agreement with values obtained from the widely used breaking thread method. DDRM enables to measure ν in polymeric blends of commercial interest—the high viscosity systems that would be very difficult to characterize by other techniques. Furthermore, for the first time it is possible to follow the time dependence of the interfacial tension coefficient, thus unambiguously determine the dynamic and equilibrium values of ν₁₂. For example, in low density polyethylene blends with polystyrene, LDPE/PS, ν decreased with the polymer-polymer contact time, t_c, from ν = 6.9 mN/m at t_c = 12 min, to ν = 5.2 mN/m at t_c ≥ 75 min—the latter may represent the true thermodynamic equilibrium value, ν₁₂. However, it is not clear whether such a reduction is exclusively due to the thermodynamically driven migration of chain-ends, low molecular weight fractions and additives, or by the thermal degradation as well. The contact time dependence of ν explained some of the differences reported for the data obtained using different measurement techniques, viz. pendant drop, capillary breakup, or ellipsoid retraction techniques. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1393–1403, 1997     

Research and application of ultralow interfacial tension oil displacement agent

An ultralow interfacial tension (IFT) oil displacement agent, which was a surfactant combinational system (HCS) with good salt and heat resistance, was synthesized using amphoteric betaine (AMS)/anionic sulfonate (AKS)/nonionic alkyl amide (NIS). The interface tensiometer was used to test the IFT. The results showed that the oil–water IFT could be as low as 10^?4 mN/m when the salinity is 10,000～50,000?mg/L, the concentration is 1～5?g/L, and the temperature is 40～80°C. The surfactant system has good emulsification stability. The displacement simulation experiments demonstrated that the increment of the recovery ratio can be up to 14.1%. The surfactant system could meet the demands of site operation.     

The relative role of coalescence and interfacial tension in controlling dispersed phase size reduction during the compatibilization of polyethylene terephthalate/polypropylene blends

The breaking thread and the sessile drop methods have been used to evaluate the interfacial tension between a polypropylene (PP) and a polyethylene-terephthalate (PET). An excellent correlation was found between the two. The breaking thread technique was then used to evaluate the interfacial tension of these blends at various levels of a styrene-ethylene butylene-styrene grafted with maleic anhydride (SEBS-g-MA) compatibilizer. In order to evaluate the relative roles of coalescence and interfacial tension in controlling dispersed phase size reduction during compatibilization, the morphology of PP/PET 1/99 and 10/90 blends compatibilized by a SEBS-g-MA were studied and compared. The samples were prepared in a Brabender mixer. For the 10/90 blend, the addition of the compatibilizer leads to a typical emulsification curve, and a decrease in dispersed phase size of 3.4 times is observed. For the 1/99 blend, a 1.7 times reduction in particle size is observed. In the latter case, this decrease can only be attributed to the decrease of the interfacial tension. It is evident from these results that the drop in particle size for the 10/90 PP/PET blend after compatibilization is almost equally due to diminished coalescence and interfacial tension reduction. These results were corroborated with the interfacial tension data in the presence of the copolymer. A direct relationship between the drop in dispersed phase size for the 1/99 PP/PET blend and the interfacial tension reduction was found for this predominantly shear mixing device. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2271–2280, 1997     

Full separation of oligomers in block copolymers of ethylene oxide and propylene oxide

In this study di‐ and triblock copolymers of ethylene oxide (EO) and propylene oxide (PO) are analyzed by using CAP for one block and adsorption for the other block. This gives a complete picture of EO‐ and PO‐based block copolymer with respect to the oligomers of both blocks. A full resolution of the individual oligomers can be achieved for both blocks up to an average molecular weight of 1000–1500 of each block.     

Phase behavior of undecane-tetradecane mixtures confined in SBA-15

Phase behavior of undecane-tetradecane (n-C11H24-C14H30, C11-C14) mixtures in bulk and confined in SBA-15 have been studied using differential scanning calorimetry. The bulk C11-C14 system shows multiple phase regions due to rotator phase. Confined in the pores of SBA-15 (pore diameters 3.8-7.8 nm), the mixtures only show a melting boundary of a straight line and a curve, respectively. In SBA-15 (17.2 nm), phase behavior of themixtures has some similarity to that of the bulk. Under confinement, the phase diagrams of the mixtures vary with the pore size, temperature, and compositions.     

Interfacial tension and acid‐base approaches to polymer interactions

A significant correlation has been shown to exist between the interfacial tension of polymer pairs and their acid‐base pair interaction. The relationship is inverse, with interfacial tensions decreasing as acid‐base interactions increase. Interfacial tensions, frequently used as an indicator of polymer compatibility, were measured by the breaking thread method at temperatures in the vicinity of 200 °C. Acid‐base pair interaction values were measured by inverse gas chromatography over wide temperature ranges. The observed correlation confirms the important contribution made by short‐range, acid‐base interactions to the observed value of interfacial tension and supports the prediction of equations based on fundamental definitions of surface forces. A collateral finding of this work is the decrease of acid‐base functionality with rising temperature for all polymers studied. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2096–2104, 2000     

Interfacial tension between a liquid crystalline polyesteramide and polypropylene obtained by dielectric spectroscopy

Dielectric spectroscopy is an unexplored technique in the elucidation of the morphology of polymer blends. Especially the appearance of interfacial polarization can reveal important information about the microstructure of a polymer blend. A model system of liquid crystalline polymer fibers lined up in a thermoplastic matrix was investigated. After heating above the melting temperature of both phases, the fibers developed distortions which grew with time. Dielectric spectroscopy was used to follow the change in shape of the distorted fibers. The use of only two frequencies made it possible to increase the number of relevant data points in the initial stages of the fiber breakup process. From these measurements it was possible to calculate the growth rate and hence the interfacial tension between the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 815–825, 1998     

Surface tension and density of binary mixtures of monoalcohols,water and acetonitrile: equation of correlation of the surface tension

Measurements of the surface tension (σ) and density (ρ) of binary mixtures of monoalcohols, water and acetonitrile at 298.15 K and at atmospheric pressure, as a function of mole fraction (x) have been made. The experimental values of the deviation of surface tension and the excess of molar volume (Δσ, V ^E) have been correlated by the Redlich–Kister equation. An empirical correlation equation is presented for the study of the surface tension of these mixtures, and comparisons are made of the experimental values of surface tension versus those obtained with the correlation equation and with other models of correlation. Finally, with the purpose of corroborating the validity of the correlation equation, the latter is applied to other reference binary mixtures.