Effect of pH on interface composition and on quality of oil-in-water emulsions made with hen egg yolk

Constituents of egg yolk are key ingredients of many food emulsions. They contribute to create an interfacial film between oil and water, which determines largely the characteristics of the emulsions. Food emulsions prepared with yolk are made at various pHs. However, the effect of pH on the adsorption of yolk constituents and on the composition of the interfacial film is not known. The present study deals with the influence of pH (3, 6 and 9), on protein interface concentration and composition, change in interfacial tension, and oil droplet diameter, of emulsions made with yolk. Emulsions were prepared as follows: 0.5% w/v of yolk; oil volume fraction: 0.375, homogenisation rate: 20 000 rpm/2 min. pH 6 provided the best conditions to prepare emulsion with yolk. The average diameter of oil droplets was lower at pH 6 (8.5 μm) than at pH 3 (11.8 μm) and pH 9 (13.5 μm). The interfacial protein concentration was higher at pH 6 (1.7 mg m⁻²) than at pH 3 and pH 9 (0.5 mg m⁻²). At pH 6, all the proteins of yolk, except phosvitin, were adsorbed at the interface and the interfacial tension at steady-state was lower (10 mN m⁻¹) than at pH 3 (15 mN m⁻¹) and pH 9 (30 mN m⁻¹). At pH 3, proteins at the interface are mainly phosvitin, and, at pH 9, some apoproteins of LDL and HDL. The pH modulates the composition of yolk proteins at the interface, mainly by modifying the net charge of the proteins causing their repulsion or dimerisation.     

Protein-poly(silicic) acid interactions at the air/solution interface

The structure of the interface generated by a spread layer of beta-casein on an aqueous colloidal poly(silicic) acid subphase is described. The results are compared with data for the protein alone spread at the air/water interface and the silicate solution. Films develop at the air-solution interface and a strong pH dependence of the interaction causing this is demonstrated. Reflectometry with X-rays and neutrons was used to probe the interaction as a function of subphase pH and film compression. Film thickness, tau/A, scattering length density, rho/A(-2), water volume fraction, phi(w), and surface coverage, Gamma/mg m(-2), were used to quantify the interfacial structure. Where possible, the X-ray and neutron data sets were co-refined enabling phi(w) to be evaluated without assumption regarding the protein density. At pH 5-7, strong protein-silicate interaction occurred, the interface comprising three regions: a discrete protein upper layer on top of a 15 +/- 2 A layer of silicated material followed by a diffuse layer that extended into the subphase.     

The Equilibria of Phosphatidylethanolamine-Cholesterol and Phosphatidylcholine–Phosphatidylethanolamine in Monolayers at the Air/Water Interface

Monolayers of phosphatidylethanolamine (PE), cholesterol (Ch), phosphatidylcholine (PC), and binary mixtures (PC-PE or PE-Ch) were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate π -A isotherms. The surface tension measurements were carried out at 20°C using an improved Teflon trough and a Nima 9000 tensiometer. The Teflon trough was filled with a subphase of triple-distilled water. Known amounts of lipid dissolved in 1-chloropropane were placed at the surface using a syringe. The interactions between phosphatidylethanolamine and cholesterol as well as phosphatidylcholine and phosphatidylethanolamine result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants of PC-PE and PE-Ch complexes. We considered the equilibrium between the individual components and the complex and established that phosphatidylethanolamine and cholesterol as well as phosphatidylcholine and phosphatidylethanolamine formed highly stable 1:1 complexes.     

The equilibria of phosphatidylcholine-fatty acid and phosphatidylcholine-amine in monolayers at the air/water interface

Monolayers of phosphatidylcholine, fatty acid and amine and binary mixtures phosphatidylcholine-fatty acid or phosphatidylcholine-amine were investigated at the air/water interface. Phosphatidylcholine (lecithin, PC), stearic acid (SA), palmitic acid (PA), decanoic acid (DA) and decylamine (DE) were used to the experiment. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. The surface tension measurements were carried out at 22°C using an improved Teflon trough and a Nima 9000 tensiometer. The Teflon trough was filled with a subphase of triple-distilled water. Known amounts of lipid dissolved in 1-chloropropane were placed at the surface using a syringe. The interactions between lecithin and fatty acid as well as phosphatidylcholine and amine result in significant deviations from the additivity rule. An equilibrium theory to describe the behaviour of monolayer components at the air/water interface was developed in order to obtain the stability constants of PC-SA, PC-PA, PC-DA and PC-DE complexes. We considered the equilibrium between the individual components and the complex and established that lecithin and fatty acid as well as phosphatidylcholine and amine formed highly stable 1:1 complexes.     

Simultaneous monitoring of protein adsorption at the solid–liquid interface from sessile solution droplets by ellipsometry and axisymmetric drop shape analysis by profile

In this paper two in situ techniques are combined to simultaneously examine protein adsorption at the solid–liquid interface from sessile solution droplets. With axisymmetric drop shape analysis by profile (ADSA-P) the change in solid–liquid interfacial tension is determined, while ellipsometry is employed to measure the amount of protein adsorbed from the same solution droplet at the solid–liquid interface. Three proteins (human serum albumin (HSA), immunoglobulin G (IgG) and fibrinogen (Fb)) were dissolved to a concentration of 0.05 mg ml⁻¹ in PBS (pH 7) and sessile droplets were placed for 2 h on a 47.8 nm thick gold coating on glass. The gold coated glass was positioned onto a quartz prism with immersion oil. The prism was aligned in a rotating analyser ellipsometer and the optical beam was thus allowed to be reflected at the hydrophobic gold surface. The ADSA-P set-up was built in 90° cross-beamed set-up around the prism. By combining the results for the adsorbed amounts and the interfacial tension changes over the two hour adsorption period, two stages in the adsorption process could be distinguished. In the first stage, the adsorbed amounts increase in correspondence with the interfacial tension changes, indicating that the interfacial tension changes are caused by adsorption, whereas in the second stage interfacial tension changes continue despite the adsorbed amounts being constant. Consequently, the second stage must be associated with conformational changes of the adsorbed proteins. For HSA and Fb, the conformational contribution to the interfacial tension changes (7.8 and 5.3 mJ m⁻², respectively) were approximately 2-fold the adsorption contribution, while for IgG both were equal around 3 mJ m⁻².     

Adsorption behavior of phospholipid vesicles at oil/water interfaces

By measuring the change in interfacial tension after adding phospholipid vesicles to an aqueous solution of electrolyte, we studied the adsorption behavior of phospholipid vesicles at oil/water interfaces. The effects of concentration of three kinds of electrolyte (NaCl, MgCl₂, LaCl₃) and of the mixing ratio of two kinds of phospholipids (phosphatidylcholine and phosphatidylserine), on the adsorption behavior at an oil/water interface were examined. The results were interpreted using the DLVO theory.     

Thermodynamic analysis of the cation binding to a phosphatidylcholine monolayer at a polarised interface between two immiscible electrolyte solutions

Thermodynamic analysis of the polarised interface between two immiscible electrolyte solutions (ITIES) was outlined, which accounts for the adsorption of phosphatidylcholine (PC) both as a zwitterion and a cation formed by the aqueous cation association with the zwitterionic PC form, as well as for the aqueous cation transfer facilitated by PC leading to its depletion from the interface. Electrocapillary equation was derived clarifying the physical significance of the surface charge density; the differential capacity and the PC surface excess concentration. The potential dependence of the interfacial tension calculated using the Damaskin’s adsorption model of a compound adsorbed in two different forms was found to agree well with that measured for the polarised water|1,2-dichloroethane interface in the presence of dl-α-dipalmitoylphosphatidylcholine. Experimentally observed effect of the nature of the aqueous cation on the interfacial tension was ascribed to the difference in the PC association constant.     

Viscoelastic properties of isomeric alkylglucoside surfactants studied by surface light scattering

Surface light scattering (SLS) by capillary waves was used to investigate the adsorption behavior of non-ionic sugar surfactants at the air/liquid interface. SLS by the subphase (water) followed predictions from hydrodynamic theory. The viscoelastic properties (surface elasticity and surface viscosity) of monolayers formed by octyl beta-glucoside, octyl alpha-glucoside, and 2-ethylhexyl alpha-glucoside surfactants were quantified at submicellar concentrations. It is further concluded that a diffusional relaxation model describes the observed trends in high-frequency, nonintrusive laser light scattering experiments. The interfacial diffusion coefficients that resulted from fitting this diffusional relaxation model to surface elasticity values obtained with SLS reflect the molecular dynamics of the subphase near the interface. However, differences from the theoretical predictions indicate the existence of effects not accounted for such as thermal convection, molecular rearrangements, and other relaxation mechanisms within the monolayer. Our results demonstrate important differences in molecular packing at the air-water interface for the studied isomeric surfactants.     

pH和光对复合型乳液拓扑结构的调控

Complex emulsions have attracted much attention because of their relevant application in various fields over the past decade. Though complex emulsions with various topologies can be created by adjusting the fraction of selected components during the homogenization processes, it is still a challenge to control the topology of complex emulsion droplets in situ using stimuli-responsive factors such as light, pH, and temperature. In this work, a three-phase complex emulsion of heptane and perfluorohexane (1:1 volume ratio) in an aqueous solution of a fluorosurfactant, F(CF₂)_x(CH₂CH₂O)_yH (Zonyl FS-300), and a synthesized pH and light dual-responsive surfactant, 1-[2-(4-decylphenylazo-phenoxy)-ethyl]-1-diethylenetriamine (C₁₀AZOC₂N₃) (both serving as emulsifiers), was prepared using the temperature-induced phase separation method. The topology of the heptane-perfluorohexane-water (H/F/W) three-phase complex emulsion was highly dependent on the concentration of C₁₀AZOC₂N₃. Light microscopy images showed that phase inversion from H/F/W to F/H/W type double emulsion via Janus emulsion was achieved by gradually increasing the concentration of C₁₀AZOC₂N₃. It was noticed that interfacial tension between heptane and an aqueous solution containing 0.1% Zonyl FS-300 (mass fraction) decreased from 28.2 to 7.4 mN∙m^-1 when the concentration of C₁₀AZOC₂N₃ was increased to 0.1% (mass fraction). The topology of the complex emulsion droplets is primarily determined by three interfacial tensions at the contact line: the H/W interface (γ_H), F/W interface (γ_F), and H/F interface (γ_HF). The reduction in interfacial tension between heptane and water was the major factor that controlled the topological transition of the complex emulsion. First, it decreases the contact angle between the H/W and H/F interfaces (θ_H). Second, it increases the contact angle between the F/W and H/F interfaces (θ_F) simultaneously. Surfactant C₁₀AZOC₂N₃ is responsive to both pH and light, and therefore, it potentially endows the fabricated complex emulsion with the corresponding stimuli-responses. Experimental results confirmed that the morphologies of complex emulsions can be tuned reversibly between Janus emulsion and F/H/W type double emulsion either by pH variation or UV/blue light irradiation. Interfacial tension measurements between heptane and water show that either protonation variation or trans-cis isomerization of C₁₀AZOC₂N₃ caused a decrease of about 5 mN∙m^-1 in interfacial tension, suggesting that the nature of pH- and light-induced morphological changes of complex emulsion droplets is the same as that induced by the changes in the concentration of C₁₀AZOC₂N₃. Correspondingly, a mechanism for the stimuli-responsive morphological change of complex emulsion was proposed based on the reduction of interfacial tension between heptane and aqueous solution interface by changing the configuration of C₁₀AZOC₂N₃ using pH alteration and light irradiation. This work provides a new approach for controlling the morphologies of complex emulsion droplets with an external double stimulus by simply introducing a dual-responsive surfactant.     

Polystyrene-b-poly(tert-butyl acrylate) and polystyrene-b-poly(acrylic acid) dendrimer-like copolymers: two-dimensional self-assembly at the air-water interface

The two-dimensional self-assembly at the air/water (A/W) interface of two dendrimer-like copolymers based on polystyrene and poly(tert-butyl acrylate) (PS-b-PtBA) or poly(acrylic acid) (PS-b-PAA) was investigated through surface pressure measurements (isotherms, isochores, and compression-expansion hysteresis experiments) and atomic force microscopy (AFM) imaging. The two dendrimer-like block copolymers have an 8-arm PS core (Mn = 10 000 g/mol, approximately 12 styrene repeat units per arm) with a 16-arm PtBA (Mn = 230 000 g/mol, approximately 112 tert-butyl acrylate repeat units per arm) or PAA (Mn = 129 000 g/mol, approximately 112 acrylic acid repeat units per arm) corona. The PS-b-PtBA sample forms stable Langmuir monolayers and aggregates into circular surface micelles up to a plateau observed in the corresponding isotherm around 24 mN/m. Beyond this threshold, the monolayers collapse above the interface, resulting in the formation of large and irregular desorbed aggregates. The PS-b-PAA sample has ionizable carboxylic acid groups, and its A/W interfacial self-assembly was therefore investigated for various subphase pH values. Under basic conditions (pH = 11), the carboxylic acid groups are deprotonated, and the PS-b-PAA sample is therefore highly water-soluble and does not form stable monolayers, instead irreversibly dissolving in the aqueous subphase. Under acidic conditions (pH = 2.5), the PS-b-PAA sample is less water-soluble and becomes surface-active. The pseudoplateau observed in the isotherm around 5 mN/m corresponds to a pancake-to-brush transition with the PAA chains dissolving in the water subphase and stretching underneath the anchoring PS cores. AFM imaging revealed the presence of circular surface micelles for low surface pressures, whereas the biphasic nature of the pseudoplateau region was confirmed with the gradual aggregation of the micellar PS cores above the PAA chains. The aggregation numbers for both samples were estimated around 3-5 dendrimer-like copolymers per circular surface micelle. These rather low values confirmed the tremendous influence of molecular architecture on the two-dimensional self-assembly of block copolymers.     

Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

The time dependence of the interfacial tension between water–acidic crude oil and water–synthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20°C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.     

Distribution of local anesthetics in lipid membranes

Absorption of local anesthetics into lipid membranes and adsorption onto their surfaces were studied as a function of the pH of aqueous bulk solutions by measuring lipid vesicle electrophoretic mobility, the partition of the anesthetics between the aqueous and membrane phases by the use of fluorescence and radioactive tracer methods, and the effect of the anesthetics on interfacial tension of lipid monolayers formed at the oil/aqueous interface.

At a pH much lower than the pK_a value of the local anesthetic, the charged form of the local anesthetic was only adsorbed onto the membrane surface, as determined from vesicle electrophoretic mobility, radioisotope tracer and the monolayer surface tension studies. Surface partition coefficients of the charged form of the local anesthetics on phosphatidylcholine and phosphatidylserine membranes were obtained from the data of electrophoretic mobilities for lipid vesicles. The surface partition coefficients of various local anesthetics paralleled those of the bulk partition coefficients.

As the pH of the solutions increased, the adsorbed amount of the charged form of the anesthetic at the membrane interface decreased, while the absorption of the uncharged form of the local anesthetic into the membrane increased. The total amount of local anesthetic adsorbed per unit area of the membrane generally increased as the pH of the solution increased. This was also observed from the measurements of the fluorescence of local anesthetics adsorbed into the membranes. At lower pH than that corresponding to the pK_a value of the local anesthetic, the amount of anesthetic adsorbed depended greatly upon the membrane surface charge. At a higher pH than its pK_a, it did not depend appreciably on the surface charge density of the membrane but did depend on the bulk partition coefficients between the aqueous and oil phases.     

Effect of pH on the adsorption kinetics of egg yolk at the triacylglycerol–water interface and viscoelastic properties of interfacial egg yolk films: a dynamic drop tensiometry study

Interfacial properties of normal egg yolk (EY), as well as stabilized, i.e. enzymatically modified with phospholipase A2, egg yolk (SEY) at the triacylglyceride (TAG) oil–water interface have been investigated with the use of the dynamic drop tensiometry (DDT) technique in the wide interval of pH values of aqueous EY solutions. We found that for both EY and SEY pH values of their aqueous solutions affect absolute values of interfacial tension at the TAG oil–water interface. In the presence of EY this effect was more pronounced, with minimum of interfacial tension values at pH nearly equal to the isoelectric point of EY proteins. For SEY solutions no clear trend was noticed, although a reduction of interfacial tension near pH 6 was also observed. Moreover, the pH-dependence of nearly steady values of interfacial tension in the presence of EY was substantially less pronounced than it has been reported previously. It was also found that there is a difference in the interfacial viscoelasticity of SEY and EY films formed at the TAG oil–water interface. Although the dependence of dilational modulus, ∣ε∣, versus surface pressure for SEY solutions goes through a maximum, absolute values of ∣ε∣ increase for EY solutions in a wide pH range. At the same time, no visible effect of pH on the viscoelasticity of EY and SEY interfacial films was noticed. It became clear from the dilational modulus versus surface pressure curves for both EY and SEY that adsorption of their surface-active components at the TAG oil–water interface occurs in a step-wise manner. We found also that the phase angle values for the adsorbed EY layers were lower that those observed in the presence of SEY, indicating an increasing viscous contribution to the dilational modulus in the SEY-containing system.     

Langmuir-Blodgett films and chiroptical switch of an azobenzene-containing dendron regulated by the in situ host-guest reaction at the air/water interface

An amphiphilic dendron containing an azobenzene ring at the focal point and the l-glutamate peripheral groups was designed. Its monolayer formation and host-guest reaction with cyclodextrins at the air/water interface and the properties of the transferred Langmuir-Blodgett (LB) films were investigated. The individual dendron, although without any long alkyl chains, could still form a stable monolayer at the air/water interface because of the good balance between hydrophilic and hydrophobic parts within the molecule. When cyclodextrin (CyD) was added to the subphase, a host-guest reaction occurred in situ at the air/water interface. The inclusion of the focal azobenzene moiety into the cavity of cyclodextrin decreased the packing of the aromatic ring and also led to the diminishment of the molecular area. Both the films formed at the surface of pure water and aqueous cyclodextrins were transferred onto solid substrates. Nanofiber structures were obtained for the film from the water surface as a result of the packing of the azobenzene groups, and circular domains were obtained for the film transferred from the aqueous CyD phases. The film transferred from the water surface showed an exciton couplet in the absorption band of azobenzene, whereas a negative Cotton effect was obtained for the film from CyD subphases. It was found that the supramolecular chirality in the LB film transferred from water was due to the transfer of the molecular chirality to the assemblies whereas that from the CyD subphase was due to the inclusion of azobenzene into the chiral cavity. Interestingly, the film from the water surface was photoinactive, whereas a reversible optical and chiroptical switch could be obtained for the film from the α-CyD subphase. The work provided a way to regulate the assembly and functions of organized molecular films by taking advantage of the interfacial host-guest reaction.     

Interfacial and self-assembly properties of bolaamphiphilic compounds derived from a multifunctional oil

The self-assembly characteristics in aqueous solutions of cationic bolaamphiphiles with systematic changes in their chemical structure is described with respect to their interfacial properties within water and at the air/water interface. Six cationic bolaamphiphiles were synthesized from multifunctional vernonia oil with the following variations: (a) two different alkyl chain lengths connecting the head groups, (b) polar ester or hydrogen bonding amide groups within the hydrophobic domain, and (c) an acetylcholine cationic head group with different conjugation sites to the alkyl chain. Surface tension measurements were used for determining critical aggregation concentration (CAC) values and air/water interfacial parameters such as 'effectiveness', surface excess concentration and area occupied by one molecule in the air/water interface. Fluorescent studies with pyrene were used to characterize CAC properties within the aqueous volume and transmission electron microscopy (TEM) for determining the aggregate structure's size, homogeneity and morphology. A bolaamphiphile molecular structure vs. interfacial property relationship was derived from this data which could be used to determine the molecular structure properties needed to generate interfacial forces to form either spherical vesicles or fibrous networks. The effects of the aliphatic chain length, head group orientation and functional groups within the hydrophobic domain on CAC, surface tension properties and self-aggregate morphology are described. Most bolaamphiphiles studied had CAC values in the 10-190 μM range, while two out of the six were found to assemble into MLM spherical vesicles with diameters ranging up to 120 nm suitable for drug delivery applications. Others formed a gelatinous network of fibers or multi-lamellar vesicles.     

Incorporation conditions guiding the aggregation of a glycosylphosphatidyl inositol (GPI)-anchored protein in Langmuir monolayers

This work investigates the process of incorporation of a glycosylphosphatidyl inositol (GPI)-anchored alkaline phosphatase into Langmuir monolayers of dimyristoyl phosphatidic acid (DMPA). Three different methods of protein incorporation were assayed. When the protein solution was injected below the air–water interface after formation of the lipid monolayer a micro-heterogeneous distribution of alkaline phosphatase throughout the interface was observed. Adsorption kinetics studied by fluorescence microscopy, associated with surface pressure measurements, led to the proposition of a model in which the protein penetration is modulated by the surface packing of the monolayer and intermolecular interactions occurring between the phospholipid and the protein. At initial surface pressures higher than 20 mN m⁻¹, the protein is quickly adsorbed on the interface and the lateral diffusion drives the alkyl chains to turn towards the air phase while the polypeptide moiety faces the aqueous subphase.     

Interfacial properties of amiodarone: the stabilizing effect of phosphate anions

Amiodarone, a drug used in heart therapy, is poorly soluble in water at room temperature, but forms transparent phases much more concentrated than the critical micellar concentration (CMC), when crystals are heated (above 60 degrees C) in presence of water and cooled down to room temperature. These pseudosolutions were supposed to be made of a complex system of micelles. In order to better understand the effects of pH and ion species on the supramolecular organization of amiodarone, interfacial pressure measurements were performed at the air/water interface on a Langmuir trough. Monolayers spread from chloroformic solutions over non bufferered subphases were insoluble at basic pH (NaOH, pH 10) but soluble at acidic pH (HCl, pH 4). However, a higher ionic strength obtained by adding NaCl (0.15 N) or NaH(2)PO(4) (0.15 N) to the subphase stopped the amiodarone solubilization. On an acidic phosphate subphase (NaH(2)PO(4), pH 4.4, 0.15 N), abnormally high surface pressures (>1 mN/m) were measured for high molecular areas (80-200 ?(2)/molecule) suggesting a supramolecular organization of the surface film. Insoluble monolayers were also obtained when the amiodarone supramolecular pseudosolution was spread on neutral (NaH(2)PO(4), pH 6.25, 0.15 N) or acidic (NaH(2)PO(4), pH 4.4, 0.15 N) subphases. However, a great instability on basic subphase (phosphate buffer pH 8.8) indicated the breakage of the supramolecular structure during spreading. These results are discussed taking into account the amiodarone state of ionization and the electrostatic interactions with counterions. Combining the use of phosphate counterions and that of acidic pH opens new perspectives in the optimization of amiodarone intravenous formulations.     

Properties of interfacial films formed by succinylated legumin from faba beans (Vicia faba L.)

The influence of succinylation on the interfacial behaviour and emulsifying properties of the main storage protein (legumin) from faba beans was studied. Results of surface tension measurements and surface shear rheometry and properties of n-decane-water emulsions indicate an increased interfacial activity by succinylation whereby the 65% succinylated legumin was the most active derivative.

The equilibrium surface pressure Π_e increased from 16.6 to 20.21 mN m⁻¹ and the critical association concentration, i.e. the subphase concentration at which the plateau of Π_e was reached, strongly decreased with succinylation from 76.6 × 10⁻⁶ to 0.84 × 10⁻⁶ g ml⁻¹. Spread and adsorbed films of legumin exhibited purely viscous behaviour under shear stress whereby the viscosity strongly increased with succinylation (from 7.93 to 93.36 μN s m⁻¹). The droplet size of legumin-stabilized emulsions decreased and the coalescence stability increased with succinylation. The comparison with acetylated legumin supports the view that the dissociated but rather globular subunit is the most interfacially active component of acylated legumin.     

Mimic oil recovery with a SDBS–dodecane–silica gel system

The wettability of the solid powder of silica gel was determined via a modified Washburn equation expressed as contact angles. The interfacial tension (γ) between the dodecane and the dilute sodium dodecyl benzene sulfonate (SDBS) aqueous solution was obtained using the spinning drop (γ<10 mN m⁻¹) or drop volume methods (γ>10 mN m⁻¹). Contact angle changes for SDBS aqueous solutions on the surface of a silica gel powder were studied. The average aggregation number of SDBS micelles in aqueous solution was determined using the fluorescence quenching method. The relationship between the wettability of the powder surface, the critical micelle concentration (CMC) of SDBS and the mimic oil recovery of the resident oil on the powder surface has been explored. It has been found that good residual oil recovery was achieved by surface wettability changes at the interfacial tensions around 4–5 mN m⁻¹, which is far from the ‘ultra low’ condition (≤10⁻³ mN m⁻¹).     

A Growing Drop Technique for Measuring Dynamic Interfacial Tension

A novel, growing drop technique is described for measuring dynamic interfacial tension due to sorption of surface-active solutes. The proposed method relates the instantaneous pressure and size of expanding liquid drops to the interfacial tension and is useful for measuring both liquid/gas and liquid/liquid tensions over a wide range of time scales, currently from 10 ms to several hours. Growing drop measurements on surfactant-free water/ air and water/octanol interfaces yield constant tensions equal to their known literature values. For surfactant-laden, liquid drops, the growing drop technique captures the actual transient tension evolution of a single interface, rather than interval times as with the classic maximum-drop-pressure and drop-volume tension measurements. Dynamic tensions measured for 0.25 mM aqueous 1-decanol solution/air and 0.02 kg/m³ aqueous Triton X-100 solution/dodecane interfaces show nonmonotonic behavior, indicating slow surfactant transport relative to the imposed rates of interfacial dilatation. The dynamic tension of a purified and fresh 6 mM aqueous sodium dodecyl sulfate (SDS) solution/air interface shows only a monotonic decrease, indicating rapid surfactant transport relative to the imposed rates of dilatation. Conversely, an aged SDS solution, naturally containing trace dodecanol impurities, exhibits dynamic tensions which reflect a superposition of the rapidly equilibrating SDS and the slowly adsorbing dodecanol.