Interfacial Tension of Aqueous Three‐Phase Systems Formed by Triton X‐100/PEG/Dextran

A novel aqueous three‐phase system was formed spontaneously when a nonionic surfactant (Triton X‐100) and two polymers (PEG and dextran) were mixed. The interfacial tension between the phases was measured by the spinning drop method. It was shown that the values of interfacial tension were extremely small. The interfacial tensions of the top/middle phases were much lower than those of the middle/bottom phases. The interfacial tension was affected by component concentrations, temperature, added salts, and the density difference between two phases. Temperature exhibited a special effect on interfacial tension: with the increase of temperature, interfacial tension increases significantly.     

Ultralow interfacial tensions in an aqueous phase-separated gelatin/dextran and gelatin/gum Arabic system: a comparison

Many protein/polysaccharide mixtures phase separate when the concentrations ofthese biopolymers are sufficiently high. One of the properties involved in this phenomenon is the interfacial tension. Here we present measurements of the interfacial tension of two different protein/polysaccharide mixtures. The protein gelatin was mixed with either dextran or gum arabic, all used in a variety of food products. The phase diagrams were constructed using optical rotation. Although both polysaccharides have the same molecular weight, the phase diagrams differed. The interfacial tension of samples, varying in the distance from the critical point, was determined using the spinning drop method. The interfacial tension was found to be in the range of 1-15 microN/m. For both systems, the scaling behavior of the interfacial tension was investigated. The investigated gelatin/dextran system gave critical exponents of 2.5+/-0.1 and 1.4+/-0.1, in reasonable agreement with the mean-field values 3 and 1.5, respectively. The gelatin/gum arabic system did not show critical behavior. For this system, the interfacial tension shows a logarithmic dependence on the distribution of the gelatin and the gum arabic molecules in the separated phases.     

Concentration dependence of the interfacial tension for aqueous two-phase polymer solutions of dextran and polyethylene glycol

We studied the interfacial tension between coexisting phases of aqueous solutions of dextran and polyethylene glycol. First, we characterized the phase diagram of the system and located the binodal. Second, the tie lines between the coexisting phases were determined using a method that only requires measuring the density of the coexisting phases. The interfacial tension was then measured by a spinning drop tensiometer over a broad range of polymer concentrations close to and above the critical point. In this range, the interfacial tension increases by 4 orders of magnitude with increasing polymer concentration. The scaling exponents of the interfacial tension, the correlation length, and order parameters were evaluated and showed a crossover behavior depending on the distance to the critical concentration. The scaling exponent of the interfacial tension attains the value 1.50 ± 0.01 further away from the critical point, in good agreement with mean field theory, but the increased value 1.67 ± 0.10 closer to this point, which disagrees with the Ising value 1.26. We discuss possible reasons for this discrepancy. The composition and density differences between the two coexisting phases, which may be taken as two possible order parameters, showed the expected crossover from mean field behavior to Ising model behavior as the critical point is approached. The crossover behavior of aqueous two-phase polymer solutions with increasing concentration is similar to that of polymer solutions undergoing phase separation induced by lowering the temperature.     

Interfacial tension in aqueous biopolymer-surfactant mixtures

The current study offers a first insight into the interfacial properties of pullulan-sodium dodecyl sulphate (SDS) aqueous two-phase systems (ATPS) in the presence of sodium chloride (NaCl). The effect of composition on the interfacial tension (sigma) in these ATPS was investigated over a wide range of pullulan, SDS and NaCl concentrations. An increase in the interfacial tension was observed with increasing pullulan and SDS concentrations and a small increase was also observed as the NaCl concentration was increased. In both cases the interfacial tension increases were closely related to the phase behaviour of these systems; as a consequence of increasing the pullulan, SDS and/or NaCl concentrations, the system moves further away from the critical point. In all systems interfacial tensions (of the order of muN/m) were comparable with those reported for polymer-polymer ATPS. Interfacial tensions sigma can be well correlated with the difference in pullulan and SDS concentrations between the phases (DeltaC pul and DeltaC SDS) and also the tie-line length (TLL); all yield straight lines on a log-log scale.     

THE RELATIONSHIP BETWEEN THE MOLAR PARTITION COEFFICIENT AND THE ULTRALOW INTERFACIAL TENSION MINIMUM IN A PETROLEUM SULFONATE/ HYDROCARBON/BRINE SYSTEM

The partitioning of a sodium petroleum sulfonate between heptane and brine yields surfactants with different molar absorptivity and λ_max values in the two phases, except near the point of minimum interfacial tension, e of the surfactant in the heptane phase increases sharply above the point of minimum interfacial tension between the two phases. The molar partition coefficient, M_H/M_W, for the surfactant between the heptane and brine phases is unity at surfactant concentrations in the brine phase below the point of minimum interfacial tension and drops sharply at concentrations above it. The critical micelle concentration of the surfactant in the aqueous phase equilibrated with the heptane phase is considerably below the concentration for minimum interfacial tension     

Mixed emulsifying agents

Summary One per cent of aluminium hydroxide and bentonite was taken in suspension and their interfacial tension was determined with kerosene oil as dispersed phase byCenco-Du Noüy Interfacial Tensiometer No. 70545 after necessary calibrations and applying the correction factorF (9). Natural colloids (gum acacia, gelatin) and soaps were added into these suspensions in various concentrations and interfacial tension was determined. It was found that the addition of natural colloids, decreases the interfacial tension and the emulsions are finer and more stable. With the increasing quantities of these natural colloids to the suspensions, a further reduction in the interfacial tension is noticed, thereby such a corresponding emulsion formed has a higher interfacial area and stability factor. Similarly copper arsenate, lead arsenate, calcium arsenate and aluminium arsenate were taken and interfacial tension was measured with the addition of various quantities of natural colloids. The results arrived at, further show the lowering of interfacial tension with the conformity of finer emulsions having higher stability factors. Bordeaux mixtures, Burgundy mixtures, and copper phosphate were also taken and similar results were arrived at as shown in table 2 and 3. The above facts reveal a relationship between sedimentation and interfacial tension; low interfacial tension to low sedimentation values represent greater wettabilities of the solids on the addition of colloidal solutions. In this way was tested quantitatively the theory that the stability of an emulsion depends on relative interfacial tension and, as an approximate correlary, on the dispersibilities or wettabilities of the emulsifier in the two phases because whatever different causes may be operative in the stabilization of different emulsions, the one fundamental underlying principle applicable to all cases is the wetting of solid agent by the two liquids. With 3 tables     

Interfacial Tension of Polyethylene Glycol/Potassium Phosphate Aqueous Two-Phase Systems

Abstract

The interfacial tension of Polyethylene glycol (PEG)/potassium phosphate two-phase systems was measured by the rotating drop method. The interfacial tension was as low as 0.001 dyne/cm and increased with increases in the total concentrations of both PEG and potassium phosphate in two-phase systems. The increase in the interfacial tension was a function of the concentration differences of PEG and potassium phosphate between the top and the bottom phases which was confirmed by the tie line analysis. The interfacial tension was affected also by the molecular weigth of PEG. At low PEG molecular weights, the increase in the molecular weight greatly increased the interfacial tension, but at high molecular weights, the interfacial tension varied less with the molecular weight.     

On the mechanism of growth of cells (Bacillus amyloliquefaciens) in the mixed aqueous two-phase system

The growth ofBacillus amyloliquefaciens in the aqueous two-phase system, made up of polyethylene glycol, dextran, and water, was investigated. Generally,Bacillus partitions in the dextran phase, but the magnitude of the separation depends largely on the overall composition of polymers in the phase system. The kinetics of growth ofBacillus amyloliquefaciens was studied in the polyethylene glycol-rich continuous phase, dextran-rich dispersed phase, and in the mixed phase. From the kinetic data it appears that increasing the overall polymer composition causes the cells to adsorp at the interface. On the other hand, partition measurements indicate that increasing polymer concentrations make the cell partitioning more one-sided. This anomaly is explained by studying the interfacial adsorption of cells via dynamic surface tension measurements.     

Partitioning and assembly of metal particles and their bioconjugates in aqueous two-phase systems

The behavior of metal nanospheres and nanowires and their bioconjugates in aqueous two-phase systems (ATPS) is described. The ATPS used in this work comprised poly(ethylene glycol) (PEG), dextran, and water or aqueous buffer. Au and Ag nanospheres less than 100 nm in diameter partition between the PEG-rich and dextran-rich phases on the basis of their surface chemistry and can be separated on this basis. Larger Au nanospheres and wires accumulate at the interface between the two aqueous phases. The influence of polymer molecular weight and concentration on interfacial assembly of Au wires is described. DNA-derivatized nanowires at the aqueous/aqueous interface retain the ability to selectively bind to fluorescent complementary DNA. In addition, Au nanoparticles have been bound to Au wires via selective DNA hybridization at the ATPS interface. Transmission electron microscopy and thermal denaturation experiments confirm that DNA-driven assembly is responsible for the formation of the nanosphere/wire assemblies. These results demonstrate the biocompatibility of the two-phase interface and point to future use as scaffolding in biorecognition-driven assembly.     

Effect of Coconut Protein and Xanthan Gum,Soybean Polysaccharide and Gelatin Interactions in Oil-Water Interface

We report on our study of the interactions between coconut protein extracted from coconut meat and three hydrocolloids (gelatin, xanthan gum, and soybean polysaccharide) and their interfacial adsorption and emulsification properties. We used Zeta potential, fluorescence spectroscopy scanning and ITC to investigate the interactions between a fixed concentration (1%) of coconut protein and varying concentrations of hydrocolloid. Through the interfacial tension and interfacial viscoelasticity, the interfacial properties of the hydrocolloid and coconut protein composite solution were explored. The physical stability of the corresponding emulsion is predicted through microstructure and stability analysis. Xanthan gum forms a flocculent complex with coconut protein under acidic conditions. Soy polysaccharides specifically bind to coconut protein. Under acidic conditions, this complex is stabilized through the steric hindrance of soy polysaccharides. Due to gelatin-coconut protein interactions, the isoelectric point of this complex changes. The interfacial tension results show that as time increases, the interfacial tensions of the three composite solutions decrease. The increase in the concentration of xanthan gum makes the interfacial tension decrease first and then increase. The addition of soybean polysaccharides reduces the interfacial tension of coconut protein. The addition of xanthan gum forms a stronger elastic interface film. Emulsion characterization showed that the gelatin-added system showed better stability. However, the addition of xanthan gum caused stratification quickly, and the addition of soybean polysaccharides also led to instability because the addition of polysaccharides led to a decrease in thermodynamic compatibility. This research lays the foundation for future research into coconut milk production technology.     

Do polysaccharides such as dextran and their monomers really increase the surface tension of water?

It has been reported in the literature that sugars such as dextrose and sucrose increase the surface tension of water. The effect was interpreted as a depletion of the solute molecules from the water-air interface. This paper presents accurate measurements of the surface tension of different concentrations of dextrose solution as well as its polymer (i.e., dextran). An automated drop shape technique called axisymmetric drop shape analysis (ADSA) was used for the surface tension determination. The surface tension measurement is presented as a function of a shape parameter, P(s), which has been used to quantify the range of the applicability of ADSA. The results of the above study show that dextrose solutions decrease the surface tension of water in contradiction to the results obtained from the weight drop method in the literature. The surface tension decreases continuously with increasing concentration. A similar effect was observed for the dextran solutions. To verify that the setup and the methodology are capable of accurately measuring increases in surface tension, a similar experiment was conducted with a sodium chloride solution with a concentration of 1 M. It is well-known that electrolyte solutions, e.g., sodium chloride, increase the surface tension of water. The results obtained from ADSA verify that the sodium chloride increases the surface tension of water by 1.6 mJ/m(2). It is concluded that dextrose and dextran decrease the surface tension of water. Thus, there is no evidence of depletion. To identify the sources of discrepancy between the results of ADSA and those reported in the literature, the experiments were repeated for different concentrations and the rate of drop formation using the drop weight method. It was found that the rate of drop formation is most likely the source of error in the results reported in the literature.     

Study of the surface and interfacial tensions in systems containing a low molar mass liquid crystal

The surface tension of a low molar mass liquid crystal (LMMLC), 4-cyano-4'-n-heptyloxybiphenyl (70CB), was measured as a function of temperature using the pendant drop method, forming drops of different volumes ranging from 5 to 11 mm³. Contact angles formed by drops of 70CB in the nematic and isotropic phases on plates of polystyrene (PS) and of a liquid crystal polymer (LCP), VECTRA A910, were also measured. Only large drops could be used for surface tension analysis. It was shown that in the nematic phase the surface tension of 70CB decreases with increasing temperature, and that in the isotropic phase the surface tension increases with increasing temperature. Using the values of contact angle and of surface tension of 7OCB it was possible to evaluate the interfacial energy between 7OCB and PS and between 7OCB and VECTRA. The interfacial energy between 7OCB and PS, and between 7OCB and VECTRA, decreased with increasing temperature for ranges of temperatures corresponding to both phases of 70CB.     

Study of the surface and interfacial tensions in systems containing a low molar mass liquid crystal

The surface tension of a low molar mass liquid crystal (LMMLC), 4-cyano-4'-n-heptyloxybiphenyl (70CB), was measured as a function of temperature using the pendant drop method, forming drops of different volumes ranging from 5 to 11 mm³. Contact angles formed by drops of 70CB in the nematic and isotropic phases on plates of polystyrene (PS) and of a liquid crystal polymer (LCP), VECTRA A910, were also measured. Only large drops could be used for surface tension analysis. It was shown that in the nematic phase the surface tension of 70CB decreases with increasing temperature, and that in the isotropic phase the surface tension increases with increasing temperature. Using the values of contact angle and of surface tension of 7OCB it was possible to evaluate the interfacial energy between 7OCB and PS and between 7OCB and VECTRA. The interfacial energy between 7OCB and PS, and between 7OCB and VECTRA, decreased with increasing temperature for ranges of temperatures corresponding to both phases of 70CB.     

Influence of bulk elasticity and interfacial tension on the deformation of gelled water-in-oil emulsion droplets: an AFM study

We used atomic force microscopy (AFM) to study the deformation and wetting behavior of large (50-250 microm) emulsion droplets upon mechanical loading with a colloidal glass probe. Our droplets were obtained from water-in-oil emulsions. By adding gelatin to the water prior to emulsification, also droplets with a bulk elasticity were prepared. Systematic variations of surfactant and gelatin concentrations were made, to investigate their effect on the deformation and wetting behavior of the droplets and to identify the contributions of interfacial tension, bulk elasticity, and expelled water. The AFM experiments were performed in force--distance mode and showed on approach a repulsive regime which in many cases was terminated by a jump-in of the probe. In the case of pure water (i.e. gelatin-free) droplets, the repulsive part of the curve showed a good linearity, thus allowing the extraction of an effective droplet spring constant. This quantity was found to decrease on raising the surfactant concentration from below the critical micelle concentration (cmc) to well above the cmc, and its numerical values were found to correspond remarkably well to literature values for the interfacial tension. Our findings indicate that, on gelatin increase inside the droplets, the bulk elasticity gradually becomes dominant and the droplets' stiffness does not depend anymore on surfactant concentration. Also the stability of the droplet interface against wetting, as measured by the force at which the jump-in instability occurs, was enhanced by gelatin. For gelatin concentrations of > or =15 wt %, the droplets were found to behave like purely elastic bodies. Both gelatin and surfactant contribute positively to the stability against interface breakup.     

Particles trapped at the droplet interface in water-in-water emulsions

Water-in-water emulsions were formed by mixing incompatible aqueous solutions of dextran and poly(ethylene oxide) (PEO) in the presence of latex or protein particles. It was found that particles with a radius as small as 0.1 μm become trapped at the interface between the PEO- and dextran-rich phases with interfacial tensions down to 10(-6) N/m. The particles were visualized at the interface of the emulsion droplets using confocal laser scanning microscopy (CLSM) allowing determination of the contact angle. Various degrees of coverage with particles could be observed. On densely covered droplets, the particles had a hexagonal crystalline order. At intermediate coverage, transient clustering of the particles was observed. The diffusion coefficient of the particles at the interface was determined using multiparticle tracking. Fusion of droplets was observed in all cases leading eventually to macroscopic phase separation.     

The effect of salting out and micellization on interfacial tension

We consider a system consisting of oil and water phases with nonionic surfactant distributed between them and present a model for the effect of salt on the interfacial tension. The model accounts for the salting out of surfactant from water to oil and also for the occurrence of micelles in the aqueous phase. In addition, it is shown that salting out affects micellization in interesting ways, e.g. micelles may form as the salt concentration increases even though none are present initially and then disappear at higher concentrations. The effect of chain length and head group size (and hence of HLB) on the interfacial tension is examined for surfactants of the polyoxyethylene type. The calculated interfacial tension decreases continuously and may become negative under certain condition, indicating that the oil-water interface becomes unstable and a microemulsion forms.     

Complexation behavior of gelatin with amphiphilic drug imipramine hydrochloride as studied by conductimetry,surface tensiometry and circular dichroism studies

Herein we report our studies carried out on the interaction between IMP and gelatin in aqueous medium at 25 °C using conductimetry, surface tensiometry and circular dichroism (CD) techniques. Both surface tensiometry and conductimetry results indicate that the drug interacts with the gelatin in a surfactant-like manner, i.e., both critical aggregation (cac) and polymer saturation points (psp) were observed. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule. The decrease in cac on increasing gelatin concentration is an indication of the strong interaction between gelatin and IMP. However, at low concentration of gelatin the interaction was not much strong as exposed by surface tension study, i.e., the cac was not very clear (as with higher gelatin concentrations). As usual, the psp increased on increasing the gelatin concentration and was always higher than the critical micelle concentration of the drug in pure aqueous medium. Using CD measurements the influence of IMP on the secondary structure of gelatin in aqueous solutions was also investigated. CD studies (performed at very low drug concentrations) illustrated that the random coil content of gelatin increases with increasing drug concentration. Free energies of aggregation (ΔG_agg) and micellization (ΔG_mic) were computed with the help of degrees of micelle ionization obtained from the specific conductivity – [IMP] plots.     

The dynamic effects of surfactants on droplet formation in coaxial microfluidic devices

Droplet emulsification in microfluidic devices involves the constant formation of fresh interfaces between two immiscible fluids. When the multiphase system contains surfactant, dynamic mass transfer of the surfactant onto the interface results in a dynamic interfacial tension different from the static interfacial tension measured in an equilibrium state. In this work, we have systematically investigated the effects of surfactant concentration and type on the dynamic interfacial tension of two different liquid-liquid two phase systems [N-hexane/water-sodium dodecyl sulfate (SDS) and N-hexane/water-cetyltrimethylammonium bromide (CTAB)] rapidly producing relatively small droplets in coaxial microfluidic devices. Dynamic interfacial tension experiments using the pendent drop method and a tensiometer were conducted, and a semiempirical equation was developed to put into context the effects of surfactants and the experimental conditions on droplet formation and dynamic interfacial tension in dynamic microchannel flows. The results presented in this work provide a more in-depth understanding of the dynamic effects of surfactants on droplet formation and the precise controllable preparation of monodispersed droplets in microfluidic devices.     

Interfacial tension between water and high pressure CO2 in the presence of hydrocarbon surfactants

Interfacial tension of water–CO₂ interface was measured by pendant drop method in the presence of a surfactant of various concentrations. The surfactants used were three surfynols which are non-ionic blanched hydrocarbon with different length of the alkyl side chain. Prior to the interfacial tension measurements, the solubility of the surfynols in CO₂ were determined from cloud point method. The measured interfacial tensions indicated that an addition of small amount surfactant did reduce the interfacial tension. The interfacial activities of surfactants were evaluated from the slope of the interfacial tension reduction curve against the surfactant concentration and rationalized in terms of the molecular natures such as hydrophobic alkyl chain length.     

Budding and asymmetric protein microcompartmentation in giant vesicles containing two aqueous phases

We report the effect of external osmolarity on giant lipid vesicles containing an aqueous two-phase system (ATPS GVs). The ATPS, which is comprised of poly(ethyleneglycol) [PEG], dextran, and water, serves as a primitive model of the macromolecularly crowded environment of the cytoplasm. Coexisting PEG-rich and dextran-rich aqueous phases provide chemically dissimilar microenvironments, enabling local differences in protein concentration to be maintained within single ATPS GVs. The degree of biomolecule microcompartmentation can be increased by exposing the ATPS GVs to a hypertonic external solution, which draws water out of the vesicles, concentrating the polymers. Enrichment of a protein, soybean agglutinin, in the dextran-rich phase improves from 2.3-fold to 10-fold with an increase in external osmolarity from 100 to 200 mmol/kg. In some cases, budding occurs, with the bud(s) formed by partial expulsion of one of the two polymer-rich aqueous phases. Budding results in asymmetry in the internal polymer and biomolecule composition, giving rise to polarity in these primitive model cells. Budding is observed with increasing frequency as external ionic strength increases, when membrane elasticity permits, and can be reversed by decreasing external osmolarity. We note that the random symmetry-breaking induced by simple osmotic shrinkage resulted in polarity in both the structure and internal protein distribution in these primitive model cells. Budding in ATPS-containing GVs thus offers an experimental model system for investigating the effects of biochemical asymmetry on the length scale of single cells.