Surface Dilatational Modulus Research Articles

Effect of Surface Dilatational Modulus on Bubble Generation in Visualized Pore‐Throat Models

AbstractIn order to illustrate the effect of surface dilatational modulus on bubble break‐up, different pore‐throat visualized models were constructed using oil–wet poly(methyl methacrylate). Bubble generation was studied by comparing the snap‐off between lauroamide propyl betaine (LAB) with low surface dilatational modulus and LAB‐myristic acid with high surface dilatational modulus. In the homogeneous pore‐throat model, when bubbles of LAB flowed through the throat, only deformation occurred and no snap‐off was observed, while for bubbles of LAB‐myristic acid, repeated snap‐offs occurred. Experiments with isolated bubbles showed that a high surface dilatational modulus facilitates liquid flowing into the throat, which causes the snap‐off. Besides, the generated small bubbles contributed to the snap‐off of other following bubbles. In the pore‐throat model with large pores, the pores supplied enough space for bubbles passing through throat side by side, which facilitated the snap‐off.

Self-regulation of foam volume and bubble size during foaming via shear mixing

Here we study the factors affecting the foam generation in a planetary mixer with a series of surfactant solutions, having different dynamic surface tensions, surface dilatational moduli and bulk viscosities. The foam generation in this device consists of three well defined periods: (1) Induction period during which very slow increase of the foam volume is observed. The duration of this period depends significantly on the shear rate during foaming and on the volume of the surfactant solution; (2) Fast increase of foam volume; the rate of this process depends primarily on the shear rate and dynamic surface tension of the solutions; (3) Plateau region in which the foam volume remains constant. The experimental results show that the processes of air entrapment ends when a certain critical (dimensionless) shear stress of the foam is reached. Depending on the bulk and surface properties of the surfactant solutions, this critical stress is achieved for foams with different air volume fractions and mean bubble sizes. Thus, when solutions with higher bulk viscosity and/or higher surface modulus are used, the critical stress is reached at lower air volume fraction and with smaller bubbles. Power-law equations are shown to describe very well the effects of the foaming shear rate and solution viscosity on the final foam volume and mean bubble size.

Foaming and air-water interfacial characteristics of solutions containing both gluten hydrolysate and egg white protein

Enzymatically hydrolyzed wheat gluten can be a viable alternative for traditional animal-based foam stabilizing proteins in food systems. Gluten hydrolysates (GHs) can be considered for (partially) replacing surface-active food proteins such as those of egg white (EW). We here studied the foaming and air-water (A-W) interfacial characteristics of mixed GH + EW protein solutions. GH solutions had much higher (P < 0.05) foaming capacities than EW solutions, while the latter had much higher (P < 0.05) foam stability than the former. When only one sixth of EW proteins was replaced by GHs, the foaming capacity of the mixtures was as high as or higher than that of the GH solutions. Furthermore, when half of the EW protein was replaced by GH, the mixtures still had high foam stability. It thus seems that both GH and EW proteins contribute positively to the foaming characteristics of the mixtures. However, measurements of the early stages of diffusion to and adsorption at the interface, plus measurements of surface dilatational moduli at the interface, both suggested that the adsorbed protein film consists primarily of GHs rather than of EW proteins. Nonetheless, FS was higher when EW proteins were present. Mixed GH + EW solutions have a higher resistance to coalescence than GH solutions. Therefore, it is hypothesized that EW proteins form a secondary protein layer below the A-W interface which is maintained by interactions with adsorbed GH constituents, thereby providing bubbles with an additional resistance to coalescence.

Global strain field mapping of a particle-laden interface using digital image correlation

HypothesisThe ability to identify the stress-strain relations correctly is critical to understanding and modeling any rheological responses of an interface. Langmuir-Pockels (LP) trough is one of the most commonly used tools for studying an interface. Most, if not all, existing studies assume a 1D uniaxial compression during a LP-trough compression experiment. It is hypothesized that the deformation field is far more complex than what is typically assumed. ExperimentsTo examine this hypothesis, we custom-built a glass-bottomed LP trough equipped with a camera to capture a series of optical images asa carbon nanotube (CNT)-laden interface is compressed. A digital image correlation (DIC) technique was then applied to the images to evaluate the global strain field during compression of the CNT laden interface. The DIC-corrected strain data were subsequently analyzed with the surface stress data to quantify the surface shear and dilatational moduli of the CNT-laden interface. FindingsOur experimental findings clearly show, for the first time, the development of a non-uniform and complex 2D strain field during compression. The local strains were further quantified and compared with the usual assumption of 1D uniaxial compression. Although the compressive strain averaged over the whole trough area closely resembles the 1D uniaxial compression strain, the 1D compression assumption underestimates the local strain by about 36% at the center of the trough, where the surface stresses are measured. This is the first study in applying the DIC technique to map out the global strain field asa particle-laden interface is compressed. The method may also be applicable to other systems with similar optical texture, allowing the correct identification of stress-strain relationship of an interface.

Effect of Surface Dilatational Modulus on Foam Flow in a Porous Medium

Abstract In order to clarify the role of surface dilatational property in foam flow in a porous medium, three systems were prepared: a system with low surface dilatational modulus and high surface tension, a system with low surface dilatational modulus and low surface tension, and a system with high surface dilatational modulus and low surface tension. By measuring the lamella number and pressure drop across the porous medium, it has been found that differing from flow in a capillary tube, a system with high surface dilatational modulus could achieve a high pressure drop in a porous medium. The conclusion drawn as to the reason is that bubbles with smaller diameter resulting from a structure induced breakup and high dilatational modulus are the main reasons. Flow experiments at 40°C also demonstrate the effect of surface dilatational modulus on the pressure drop.

A parameter predict ing the foam stability of mixtures of aqueous ionic amphiphile solutions with indifferent electrolyte

Sodium dodecyl sulfate (SDS) is a well-defined model substance for anionic molecular surfactants. Aqueous mixtures of SDS in a surface chemically purified state and high purity NaCl were studied with respect to their equilibrium and dynamic surface tensions at a constant mean ionic activity Imean of 1mmolL−1. All studied solutions possessed the same equilibrium surface tension, however they showed striking differences in foam column and foam lamella stability experiments. This observation suggested the interpretation of the results in terms of dynamic interfacial properties. Oscillating bubble experiments were conducted to determine the frequency dependence of the surface dilatational modulus in a range from 5 to 400Hz. The obtained surface dilatational modulus could be described by the extended Lucassen-van den Tempel (LvdT) model, which allows capturing dissipative processes by the intrinsic surface viscosity κ within the interfacial region. A new parameter derived from the fitting parameters of the LvdT model correlates reasonably with direct measurements of the solutions’ foam stability. The data suggest the important role of surface rheology for the stability of foams.

Multiscale evaluation from one bubble to the foam of surface active properties of cellulose derivatives used for a starchy model sponge cake

Interfacial properties of cellulose derivatives (HPMC and MC) were studied to understand their role in structuring a foam during the whipping process. Multiscale studies were performed to explain macroscopic observations with microscopic mechanisms. Results showed that HPMC was more flexible and had higher viscosity and shear-thinning properties than MC, which in turn diffused quicker to the interface due to a smaller molecular weight. Both hydrocolloids showed a good ability to stabilize interfaces through their surface tensions and dilatational moduli measured by static and dynamic tensiometry, respectively. However, only HPMC and HPMC + MC solutions were able to develop a stable foam. Methylcellulose formed more rigid interfaces and the interfacial elasticity was probably too high, leading to a difficult fractionation of bubbles. Moreover, its lower viscosity measured at low shear rate could explain its incapability to retain bubbles in the bulk just after their formation. HPMC and MC display complementarity and synergistic effects when used together, since a foam with much smaller bubbles is formed after only 2 min of whipping this mix. The bubble size was immediately smaller for solutions of HPMC + MC than for HPMC alone, with similar final air quantity. Finally, a hypothesis about the structuring mechanism of cellulose derivatives at air/water interfaces was proposed. MC would adsorb first at the interface and stabilize it but also increase its rigidity too much, hence its fragility against high mechanical stress. HPMC would come afterwards to the interface, but through its higher flexibility it would contribute to a higher resistance of the interface.

Effect of organic acid on lauroamide propyl betaine surface dilatational modulus and foam performance in a porous medium

ABSTRACTThe purpose of this work was to study the effect of surface tension and surface dilatational modulus on foam performance in high-salinity water in a porous medium. In order to clarify the role of the surface dilatational property in foam flow in a porous medium, three systems were established: a system with low surface dilatational modulus and high surface tension, a system with low surface dilatational modulus and low surface tension, and a system with high surface dilatational modulus and low surface tension. Measurement of dilatational modulus and surface tension showed that lauroamide propyl betaine (LAB) could not reduce surface tension and that surface dilatational modulus was low. The addition of lauric acid (LCOOH) to LAB could not achieve high surface dilatational modulus; however, it could reach lower surface tension. The addition of myristic acid (MCOOH) to LAB could achieve high surface dilatational modulus and lower surface tension. Unlike the other two systems, the results of a dilatational modulus comprised of a mixture of MCOOH and LAB were not a constant, as demonstrated by varied surface area deformation outcomes. With the increase of deformation, surface dilatational modulus decreased. Results of foam flow tests showed that among the two lower surface dilatational modulus systems, LAB foam had higher flow resistance regardless of flow rate. Among the two systems of similar lower surface tension, the mixture of LAB and MCOOH showed higher flow resistance than the mixture of LAB and LCOOH. However, with the increase of flow rate, pressure differences between the two systems became smaller, which corresponded to the decrease of surface dilatational modulus with an increase of deformation.

Exploring the Relationship between Structural and Air-Water Interfacial Properties of Wheat (Triticum aestivum L.) Gluten Hydrolysates in a Food System Relevant pH Range.

The relationship between structural and foaming properties of two tryptic and two peptic wheat gluten hydrolysates was studied at different pH conditions. The impact of pH on foam stability (FS) of the samples heavily depended on the peptidase used and the degree of hydrolysis reached. Surface dilatational moduli were in most, but not all, instances related to FS, implying that, although the formation of a viscoelastic protein hydrolysate film is certainly important, this is not the only phenomenon that determines FS. In contrast to what might be expected, surface charge was not a major factor contributing to FS, except when close to the point-of-zero-charge. Surface hydrophobicity and intrinsic fluorescence measurements suggested that changes in protein conformation take place when the pH is varied, which can in turn influence foaming. Finally, hydrolyzed gluten proteins formed relatively large particles, suggesting that protein hydrolysate aggregation probably influences its foaming properties.

Simulation Studies on the Role of Lauryl Betaine in Modulating the Stability of AOS Surfactant-Stabilized Foams Used in Enhanced Oil Recovery

The stability of foam in the presence of oil is of fundamental interest in enhanced oil recovery processes using foam for mobility control. Experimentally, it is known that lauryl betaine (LB) increases foam stability of certain anionic surfactants, and LB is referred to as a foam booster. However, the molecular basis for this effect is not well understood. Using molecular dynamics simulations, here we study a system of LB and alpha olefin sulfonate (AOS-14), an anionic surfactant that is used as a foam stabilizer. We monitor the area per molecule, a quantity that correlates with the surface shear viscosity, and the surface dilatational modulus to infer the stability of the various mixtures. We find that the influence of LB is nonmonotonic: the area per molecule and surface dilatational modulus have a minimum and maximum, respectively, around 30% LB in the monolayer. We show that this net effect has its basis in two competing effects: the favorable interaction between LB and AOS-14 that tends to shrink th...

Effect of glycation and limited hydrolysis on interfacial and foaming properties of bovine β-lactoglobulin

The effect of limited hydrolysis followed by glycation with galactose, and vice versa, on interfacial and foaming (foamability and foam stability) properties of β-lactoglobulin (β-Lg) at pH 7 and pH 5 has been studied. Hardly any effect of the two treatments, hydrolysis and glycation (HG) or glycation and hydrolysis (GH), on the β-Lg foaming capacity at both pH values was observed. Foam stability, however, was significantly enhanced after both HG and GH at pH 5. Particularly, the system obtained after glycation at 50 °C followed by limited hydrolysis showed an exceptional stability, which might be related to the increase in elastic character and cohesion of the interfacial film, indicated by the increase of the surface dilatational modulus (E) and the decrease of the phase angle (ϕ) over the time. These results indicated that glycation of β-Lg with galactose followed by limited hydrolysis might allow extending the use of this protein as foaming agent, although further research in complex food systems is needed to apply this method in the formulation of acidic foods and beverages.

Effect of organic acid chain length on foam performance in a porous medium

ABSTRACTWe have systematically studied the effect of organic acid chain length on surface dilatational properties and foam flow performance in a porous medium. Surface dilatational properties were studied by oscillating drop module (ODM). ODM results in deionized water show that sufficient long chain length of organic acid is an essential requirement for high surface dilatational modulus. While, to various salinities, surfactant to acid ratio of achieving high surface dilatational modulus varies. Foam flow tests show that surface dilatational modulus has decisive effect on produced foam size, which partially determines foam flow pressure drop. Both surface dilatational modulus and surface tension determine foam flow pressure drop. Besides, surface loss modulus also contributes to pressure drop. Bulk foam tests show that addition of organic acids with proper chain length can enhance foam tolerance to oil significantly. Compared with alkane chain length, acid with longer chain has good ability in stabilizing foam. At last, foam flooding tests show that surface dilatational modulus and foam tolerance to oil play important roles in foam enhanced oil recovery.

β-Lactoglobulin adsorption layers at the water/air surface: 2. Dilational rheology: Effect of pH and ionic strength

The dynamic surface pressure Π and the two components E’ (real part) and E” (imaginary part) of the dynamic surface dilational modulus of adsorbed β-lactoglobulin (BLG) layers at the water/air interface were measured by oscillating drop/bubble profile analysis tensiometry with the aim to enlarge information on the surface rheology of solutions of this practically important protein. The effects of the solution pH and ionic strength (represented by the buffer concentration Cbuff) on the kinetic dependences of Π, E’ and E” were monitored for various protein concentrations in the range 5×10−9–2×10−4M. Combining the E’(t) and E”(t) data with the Π(t) data allowed for obtaining the dependences E’(Π) and E”(Π). The real part E’ was found to increase monotonically with increasing Π, while the E”(Π) data exhibit a maximum in the surface pressure range 14–18 mN/m. The height of the maximum in the E”(Π) dependence was found to increase with increasing protein concentration. Apparently, in these interfacial layers, relaxation processes take place and their relaxation strengths depend on the history of the layer formation, i.e. the rate of adsorption. After the maximum in the E”(Π) dependence the E”-values progressively diminish, which can be assumed to occur due to solidification of the protein gel-like network accompanied by less energy dissipation and high elasticity of the interfacial layer. BLG layers at pH 5 (close to the isoelectric point pI≈5.1) exhibit the highest E’-values and the lowest E”-values measured in this study, which suggest the formation of a strong protein network at these (isoelectric) conditions. Variations of the buffer concentration strongly influence the kinetic dependences of E’ and E” for BLG layers at pH≠pI, while at pH→pI no effect was detected. The viscoelastic characteristics of BLG layers adsorbed from buffer-free solutions containing NaCl or CaCl2 were also studied. For the first time, hysteresis in the frequency dependence of the surface dilational modulus of protein layers measured during repeating cycles of oscillations is reported. Such hysteresis is typical for BLG layers adsorbed at any solution conditions used in this study.

The Role of Surface Viscosity in the Escape Mechanism of the Stenus Beetle.

Beetles of the species Stenus comma live and hunt close to ponds and rivers, where they occasionally fall on the water surface. To escape this jeopardized state, the beetle developed a strategy relying on the excretion of a secretion containing the substances stenusine and norstenusine. They reduce surface tension and propel the bug to the saving river bank. These substances were synthesized and analyzed with respect to their equilibrium and dynamic adsorption properties at the air-water interface (pH 7, 23 ± 1 °C). The surface dilatational rheological characteristics in a frequency range from 2 to 500 Hz at molar bulk concentrations of 20.6 mmol L(-1) were studied using the oscillating bubble technique. Both alkaloids formed surface viscoelastic adsorption layers. The frequency dependence of the surface dilatational modulus E could successfully be described by the extended Lucassen-van den Tempel model accounting for a nonzero intrinsic surface viscosity κ. The findings confirmed a dual purpose of the spreading alkaloids in the escape mechanism of the Stenus beetle. Next to generating a surface pressure, a transition to surface viscoelastic behavior of the adsorbed layers was observed.

Effect of Alkyl Chain Length on the Interfacial Dilational Properties of Hydroxy-Substituted Alkyl Benzenesulfonates

Dilational rheological behaviors of adsorption layers of three surfactants, sodium 2-hydroxy-3,5-dioctyl benzene sulfonate (C8C8), sodium 2-hydroxy-3-octyl-5-decyl benzene sulfonate (C8C10), and sodium 2-hydroxy-3-octyl-5-dodecylbenzenesulfonate (C8C12) formed at air–water and decane–water interfaces, have been investigated as a function of concentration and frequency (0.002–0.1 Hz) by the oscillating bubble/drop method. The experimental results show that the dilational moduli of hydroxy-substituted alkyl benzenesulfonates are obviously higher than those of the common surfactants, because the interfacial interactions between alkyl chains are improved drastically by the unique arrangement of C8C8 molecules at the interface. However, the moduli at the decane–water interface are much lower than those at the surfaces because decane molecules will insert into the surfactant molecules adsorbed at the interface and destroy the interactions between alkyl chains. With an increase in the number of carbon atom of 5-alkyl, the surface dilational modulus decreases because the orientation of the surfactant molecules at the surface varies from parallel to tilt. On the other hand, the diffusion-exchange process dominates the interfacial behavior and the interfacial modulus improves with the increase in the length of the alkyl chain.

Automated system for measuring the surface dilational modulus of liquid–air interfaces

The surface dilational modulus is a crucial parameter for describing the rheological properties of aqueous surfactant solutions. These properties are important for many technological processes. The present paper describes a fully automated instrument based on the oscillating bubble technique. It works in the frequency range from 1 Hz to 500 Hz, where surfactant exchange dynamics governs the relaxation process. The originality of instrument design is the consistent combination of modern measurement technologies with advanced imaging and signal processing algorithms. Key steps on the way to reliable and precise measurements are the excitation of harmonic oscillation of the bubble, phase sensitive evaluation of the pressure response, adjustment and maintenance of the bubble shape to half sphere geometry for compensation of thermal drifts, contour tracing of the bubbles video images, removal of noise and artefacts within the image for improving the reliability of the measurement, and, in particular, a complex trigger scheme for the measurement of the oscillation amplitude, which may vary with frequency as a result of resonances. The corresponding automation and programming tasks are described in detail. Various programming strategies, such as the use of MATLAB® software and native C++ code are discussed. An advance in the measurement technique is demonstrated by a fully automated measurement. The instrument has the potential to mature into a standard technique in the fields of colloid and interface chemistry and provides a significant extension of the frequency range to established competing techniques and state-of-the-art devices based on the same measurement principle.

The influence of highly charged Ce4+-cations on aqueous solutions of SDS

The surface dilatational modulus E is a fundamental system parameter of aqueous surfactant solutions which plays an important role in the physic of foams. In this contribution, we study the influence of highly charged Cerium-ions (Ce4+)-on the surface dilatational modulus E of aqueous sodium dodecyl sulfate (SDS) solutions. The E-modulus has been determined at two concentrations below the critical micellar concentration (cmc) in the frequency range from 3Hz to 500Hz using the oscillating bubble technique. The presence of Ce4+-ions increases the surface activity of the surfactant leading to a shift of the equilibrium surface tension isotherm to lower concentrations. The cmc is reduced to 2×10−3molL−1. Adsorption layers of aqueous SDS solutions exhibit a surface visco-elastic behavior. The magnitude and the phase of the complex dilatational modulus E increase in a continuous fashion with the frequency indicating a dissipative process within the adsorption layer. The presence of the electrolyte modifies the frequency characteristics of the complex modulus towards the features of a surface elastic system. Furthermore there are pronounced changes in the stability of the corresponding foams. The lifetime of wet foam lamella is significantly reduced by the presence of the Ce4+-ions. The results provide evidence for the decisive impact of surface visco-elastic properties on foam stability of aqueous surfactant solutions.

Surface property and enhanced oil recovery study of foam aqueous dispersions comprised of surfactants–organic acids–nanoparticles

With a higher surface dilatational modulus, the diameter of the produced foam has a narrower distribution.

Modulating interfacial dilatational properties by electrostatic sodium caseinate and carboxymethylcellulose interactions

The interactions between sodium caseinate (NaCas) and carboxymethylcellulose (CMC) in aqueous solution influenced by pH and CMC concentration were assessed by visual observation, measuring turbidity, ζ-potential, particle size and rheological tests. Effects of CMC on the interfacial dynamic properties of NaCas were investigated using an automatic pendant drop tensiometer. The results indicated that CMC adsorbed onto NaCas mainly through electrostatic interactions in solution at pH ≤ 5.5. and their interactions revealed a significant influence on the dynamic characteristics of NaCas adsorbed films. For surface pressure (π) and surface dilatational modulus (E) values, they were both changed in response to the presence of CMC in the bulk phase at pH 5.5 and 4. Especially for the E values of films, which showed a continuous increase as function of CMC concentration. However, the presence of CMC in the bulk phase had no significant effect on the adsorption of NaCas molecules at pH 7, indicating the interface was dominated by the protein.

Impact of pectin or chitosan on bulk, interfacial and antioxidant properties of (+)-catechin and β-lactoglobulin ternary mixtures

The interactions effect between (+)-catechin, β-lactoglobulin and two types of polysaccharides (pectin and chitosan) were studied at pH 4.Dynamic light scattering (DLS) revealed that pectin formed smaller complexes in the presence of (+)-catechin and β-lg, while chitosan presented a reduced number of populations with higher particle size. Dynamic interfacial data (obtained by a drop tensiometer) revealed that the complexes formed between pectin (+)-catechin and β-lg slowed down the β-lg migration to the oil/water interface; contrarily to the chitosan mixtures where protein migrated faster. The surface dilatational modulus of β-lg was ∼45 mN/m and increased to ∼60 mN/m when mixing with pectin and (+)-catechin, while the values of the surface dilatational modulus for the chitosan mixed interfacial films decreased to ∼35 mN/m. The free (+)-catechin content decreased 12% and 10% when interacting with pectin and chitosan, respectively, as compared to pure (+)-catechin. However, the (+)-catechin antioxidant activity were not affected by the interactions. Complexes formed between polyphenols, proteins and polysaccharides could be used as a good alternative to understand and consequently improve the phytochemicals stability in food matrices.