Dynamic Surface Tension Behavior Research Articles

Dynamic interfacial properties and foam behavior of licorice root extract solutions

Licorice (Glycyrrhiza glabra) is a useful plant of the family Fabaceae, with sweet-tasting roots. The root extract of this plant is rich in saponins, so it can be considered a source of natural surfactants. This research provides some applicable information about the dynamic surface tension and foam behavior of aqueous solutions of licorice root extract (LRE). The pendant drop shape analysis was utilized to study the surface tension and dilational surface rheology of LRE at the water/air interface. The Bikerman type experiment was used to measure foamability and foam stability of aqueous LRE solutions. The equilibrium surface tensions reveal that the LRE contains surface-active components and is capable of reducing the surface tension by 25 mN/m at the critical aggregation concentration (CAC). The surface dilational visco-elasticity measurements proved that the adsorption layers are predominantly of elastic nature. Also the foamability and foam stability show a meaningful correlation with the dynamic surface properties. This study aims to contribute to the development of appropriate utilization of the benefits provided by a biosurfactant source in foam-related commercial applications.

Equilibrium and Dynamic Surface Tension Behavior in Colloidal Unimolecular Polymers (CUP).

Studies of the interfacial behavior of pure aqueous nanoparticles have been limited due tothe difficulty of making contaminant-free nanoparticles while also providing narrow size distribution. Colloidal unimolecular polymers (CUPs) are a new type of single-chain nanoparticle with a particle size ranging from 3 to 9 nm, which can be produced free of surfactants and volatile organic contents (VOCs). CUP particles of different sizes and surface charges were made. The surface tension behavior of these CUP particles in water was studied using a maximum bubble pressure tensiometer. The equilibrium surface tension decreased with increasing concentration and the number of charges present on the surface of the CUP particles influences the magnitude of the interfacial behavior. The effect of electrostatic repulsion between the particles on the surface tension was related. At higher concentrations, surface charge condensation started to dominate the surface tension behavior. The dynamic surface tension of CUP particles shows the influence of the diffusion of the particles to the interface on the relaxation time. The relaxation time of the CUP polymer was 0.401 s, which is closer to the diffusion-based relaxation time of 0.133s for SDS (sodium dodecyl sulfate).

Dynamic interfacial properties of sugar-based surfactants: Experimental study and modeling

Careful investigation about dynamic adsorption properties of surfactant molecules has a tremendous interest for their practical applications. The intention of this article is to study the dynamic adsorption properties at air/water interface for 16 nonionic sugar-based surfactants with gradual structure variation. Based on obtained results the dynamic surface tension (DST) behaviour of glycolipids was found to depend on both hydrophobic chain length and bulk concentration of surfactant. Interestingly, the plot of the maximum rate of surface tension decrease against the surfactant bulk concentration showed a linear trend for all studied surfactants independently of their structure. Furthermore, it was confirmed that all molecules were gathered on one unique curve representing a plot of the limit elasticity versus the relative surface concentration of surfactant. The using approach provided further insight into the anticipation of the dynamic surface properties of sugar-based amphiphiles.

Salt Effects on Formation and Stability of Colloidal Gas Aphrons Produced by Anionic and Zwitterionic Surfactants in Xanthan Gum Solution

This work is devoted to the influence of NaCl salt concentration on the formation and stability of colloidal gas aphrons (CGA) produced by the anionic surfactant sodium dodecyl sulfate (SDS) and zwitterionic surfactant coco amido propyl betaine (CAPB) in the presence of xanthan gum (XG) as a stabilizer. Dynamic surface tension measurements as well as volume and half-life time of the produced foams are considered for stability analysis. A sharp decrease of the half-life time and volume of the CGAs at NaCl concentrations larger than 20,000 ppm was observed, which was attributed to the precipitation of SDS in the solution. The mentioned SDS precipitation altered the dynamic surface tension behavior, dilational surface elasticity, and turbidity of the solution. The main reason for the precipitation of SDS is the increased Krafft point caused by the addition of salt. However, for the zwitterionic surfactant CAPB, the effects of added NaCl on the interfacial properties required for CGAs production was negligible due to the simultaneous effects on the cationic and anionic head groups in the CAPB leading to negligible changes in the net repulsion forces. Yet, an overall reduction in the half-life time of CGAs with increasing salt concentration, even when we have no precipitation, was observed for both surfactants, which could be explained by the reduction in the ability of XG to increase the viscosity with increasing salt concentration.

Emanating Jets As Shaped by Surface Tension Forces.

We show that emanating jets can be regarded as growing liquid towers, which are shaped by the twofold action of surface tension: first the emanated fluid is being accelerated back by surface tension force, herewith creating the boundary conditions to solve the shape of the liquid tower as a solution of an equation mathematically related to the hydrostatic Young−Laplace equation, known to give solutions for the shape of pending and sessile droplets, and wherein the only relevant forces are gravity g and surface tension γ. We explain that for an emanating jet under specific constraints all mass parts with density ρ will experience a uniform time dependent acceleration a(t). An asymptotic solution is subsequently numerically derived by making the corresponding Young−Laplace type equation dimensionless and by dividing all lengths by a generalized time dependent capillary length λc(t) = . The time dependent surface tension γ(t) can be derived by measuring both time dependent acceleration a(t) and time dependent capillary length λc(t). Jetting experiments with water and coffee show that the dynamic surface tension behavior according to the emanating jet method and with the well-known maximum bubble pressure method are the same, herewith verifying the proposed model.

Impact of triblock copolymers on the biophysical function of naturally-derived lung surfactant

The current study aimed at investigating the general applicability of triblock copolymers consisting of poly(ethylene glycol) and poly(propylene glycol) (Pluronic®) as excipients for lung delivery. After thorough physicochemical characterization of the diverse polymers, their cytotoxicity was evaluated using alveolar epithelial cells. Next, a naturally-derived lung surfactant was challenged with the distinct triblock copolymers with respect to changes in microstructure, adsorption to the air/liquid interface and dynamic surface tension behavior under bubble pulsation.Biocompatibility assessment of triblock copolymers in A549 cells demonstrated some cytotoxicity, dependent on the hydrophobicity and dose of the substance applied (effective at ≥0.1mg/ml). Supplementing triblock copolymers onto Alveofact® had an obvious influence on the aggregation state and surface activity (>25 and >5mN/m during adsorption and bubble pulsation, respectively) of the lung surfactant. Interestingly, Pluronic® F127, a rather hydrophilic triblock copolymer, showed the most intense effect on the microstructure and biophysical performance of Alveofact®. This is likely due to the synergistic interplay of its low critical micelle concentration and rather high molecular weight, leading to the penetration of lung surfactant film/vesicles and accompanied by a partial replacement of relevant surfactant components from the air/liquid interface.Overall, suitable compositions and concentrations of triblock copolymers were identified with respect to compatibility with the physiological environment of the deep lungs.

Static and dynamic surface tension behaviour of a triblock copolymer and a non ionic surfactant mixture

Abstract Static and dynamic surface tension measurements have been carried out on mixtures of a commonly used block copolymer Pluronics ® P123 and a non-ionic surfactant polyoxyethelene (9) lauryl ether (C 12 E 9 ) to understand the block polymer-surfactant interactions. The effects of the interaction on the adsorption and micellisation behaviour have also been studied. Three different compositions comprising 3:1, 1:1 and 1:3 molar ratios of Pluronic P123 and C 12 E 9 have been investigated and the results are compared with the data of pure P123 and C 12 E 9 solutions. It has been observed that the nature and magnitude of the polymer surfactant interactions depend on the composition of the mixtures. The mixture containing 3:1 molar ratio of P123 and C 12 E 9 shows synergistic effect with a negative value for the interaction parameter (β), as obtained from the analysis of surface tension data using Rubingh’s model. However, for the other two compositions (i.e., 1:1 and 1:3 molar ratios), the equilibrium surface tension data show premicellar adsorption and aggregation of the surfactant molecules on the polymer chain. The dynamic surface tension (DST) results indicate that the strong polymer surfactant interactions, as reflected in the equilibrium surface tension data, do not modify the DST behaviour significantly from that of pure components. This is attributed to the dominant effect of the polymer adsorption at the interface, during the short time scale studied.

Visualization of Multiscale Processes - Bubble Dynamics in Surface Active Colloids

The growth dynamics of isolated gas bubbles from a submerged capillary-tube orifice in a pool of aqueous solution of Cetyl Trimethyl Ammonium Bromide (CTAB) was studied by multi-scale modeling. The macro-scale bubble ebullience is controlled by the molecular scale surfactant adsorption/desorption on the liquid-gas interface. Molecular dynamics simulations were carried out to predict the interfacial adsorption/desorption kinetics. The results of the molecular dynamics simulations were input to the volume-of-fluid based macro-scale computations. The size and shape of bubbles from incipience to departure were measured using high speed videography for model validation. Predictions of the multi-scale model agree with the experimental measurements of bubble size evolution and bubble diameter at departure. The surfactant mass transfer and adsorption on the liquid gas interface gives rise to dynamic surface tension. As a result of the surfactant presence, the bubble departure diameters were smaller in CTAB solution compared to pure water. Furthermore, dynamic surface tension behavior of CTAB makes the bubble departure diameter a function of bubble Reynolds number (Re based on the orifice diameter and air flow rate). At low flow rates or low Re, the bubble departure diameters are smaller than those in water. As the air flow rate increases, the bubble departure diameters tend towards those in pure water. The authors gratefully acknowledge funding from AFOSR Thermal Science Program and AFRL DoD Supercomputing Resource Center for computing time and resources.

Equilibrium and Dynamic Surface Tension Behavior of Triblock Copolymer PEO-PPO-PEO in Aqueous Medium

Equilibrium surface tension of water-soluble triblock copolymer PEO-PPO-PEO (Pluronics) has been measured to determine critical micelle concentration (CMC). The equilibrium surface tension data have been fitted with Langmuir adsorption isotherm. Dynamic surface tension (DST) of the polymer solutions has been measured at below and above the CMC. Results have been compared with the data of a typical nonionic surfactant C12E9. Significant difference in behavior of DST has been observed, with the P123 showing very slow relaxation below the CMC. Above CMC, DST data of P123 show a long induction period. However, relaxation time has been found to be comparable to C12E9. Ward and Tordai model with Langmuir adsorption isotherm has been used to fit the DST data of P123. Similarly C12E9 data from the literature have been fitted with Ward and Tordai model. A reasonably good fit has been obtained for C12E9, although the long-time data deviate from the model. The model has been found to be inadequate for the triblock copolymer that has been attributed to the change in configuration of the polymer at the surface after adsorption.

PS-286 Surfactant (s) Supplemented With Budesonide (b) For Prevention Of Bronchopulmonary Dysplasia – Biophysical And Chemical Stability Of S/b Mixture: Abstract PS-286 Table 1

Background and aims Intra-tracheal instillation of budesonide (B) using surfactant (S) as a vehicle significantly improved pulmonary status. The stability of the S/B mixture has not been studied. The aim of study is to investigate if S can be used as an vehicle to facilitate B delivery in rats and if the S/B mixture is biophysically and chemically stable. Methods and materials A Nano/PET digital scan was performed on rat that was intratracheally injected with S/18-F labelled B mixture, with 18-F-B only, or with free 18-F. The 18-F radioactivity was measured at 30 min. after injection. To test biophysical property, the dynamic surface tension behaviour of S/B suspension was conducted in Surfactometer. HPLC was performed with various S/B concentration ratios within 24 hrs after S/B mixing. Results 1) 18-F-B radioactivity was detected more in the peripheral lung in rat supplemented with S than in rat without S. 2) using a concentration of S/B ≥ 50:1, the dynamic surface activity of S was minimally affected 3) HPLC analysis revealed no new compound detected within 24 h after mixing of S/B Conclusions S can be used as an effective vehicle and that, with a S/B ratio of ≥ 50, the mixture is biophysically and chemical stable.

Dynamic Surface Tension Behavior of Liquid Iron during Carburization and Decarburization Processes

Dynamic Surface Tension Behavior of Liquid Iron during Carburization and Decarburization Processes

Biophysical inhibition of synthetic vs. naturally-derived pulmonary surfactant preparations by polymeric nanoparticles

Reasonable suspicion has accumulated that inhaled nano-scale particulate matter influences the biophysical function of the pulmonary surfactant system. Hence, it is evident to provide novel insights into the extent and mechanisms of nanoparticle–surfactant interactions in order to facilitate the fabrication of safe nanomedicines suitable for pulmonary applications.Negatively- and positively-charged poly(styrene) nanoparticles (diameters of ~100nm) served as model carriers. Nanoparticles were incubated with several synthetic and naturally-derived pulmonary surfactants to characterize the sensitivity of each preparation to biophysical inactivation. Changes in surface properties (i.e. adsorption and dynamic surface tension behavior) were monitored in a pulsating bubble surfactometer.Both nanoparticle formulations revealed a dose-dependent influence on the biophysical behavior of all investigated pulmonary surfactants. However, the surfactant sensitivity towards inhibition depended on both the carrier type, where negatively-charged nanoparticles showed increased inactivation potency compared to their positively-charged counterparts, and surfactant composition. Among the surfactants tested, synthetic mixtures (i.e. phospholipids, phospholipids supplemented with surfactant protein B, and Venticute®) were more susceptible to surface-activity inhibition as the more complex naturally-derived preparations (i.e. Alveofact® and large surfactant aggregates isolated from rabbit bronchoalveolar lavage fluid).Overall, nanoparticle characteristics and surfactant constitution both influence the extent of biophysical inhibition of pulmonary surfactants.

Flow behaviour, linear viscoelasticity and surface properties of chitosan aqueous solutions

A study of rheological properties of chitosan solutions was carried out in terms of polymer concentration (0.05–2.5 wt%) and temperature (5–25 °C). The chitosan solutions studied exhibited Newtonian behaviour at concentrations lower than 0.25 wt%. Above this value, the rest of the systems showed shear-thinning behaviour. The viscoelastic properties of chitosan solutions above 0.25 wt% were characterized by oscillatory shear measurements under small-deformation conditions and the results showed fluid-like viscoelastic behaviour. Time-concentration and time-temperature superposition methods were carried out to obtain an overall master curve; where the rheological properties of chitosan solution at a specific temperature or concentration can be predicted over a broad time scale. The fact that the activation energy for steady shear flow was higher than for oscillatory shear promoted deviations from the Cox–Merz rule, when temperature was decreased at the highest chitosan concentration studied In addition, their dynamic surface tension behaviour and surface viscoelastic properties were explored. The time-dependent decrease in surface tension along with the limiting elasticity of the interface seems to indicate that commercial chitosan may play the role of an emulsifier as well as a stabiliser of O/W emulsions.

Adsorption Layer Characteristics of Mixed SDS/CnEOm Solutions. 3. Dynamics of Adsorption and Surface Dilational Rheology of Micellar Solutions

The dynamic surface tensions of mixed SDS/C(12)EO(5) and SDS/C(14)EO(8) micellar solutions measured over a wide time range (0.1 ms to 10,000 s) at various mixing ratios are described satisfactorily by a theoretical model for the kinetics of adsorption of surfactant mixtures using the surfactant adsorption parameters obtained for premicellar mixed solutions. Additional relations used for the description of the adsorption kinetics from micellar solutions were expressions of the effective diffusion coefficient of monomers accounting for the disintegration of micelles. The modeled dynamic surface tensions agree well with the experimental data for all studied surfactant mixtures. The rheological behavior of the same mixtures--the dependencies of the viscoelasticity modulus and phase angle--were studied by using the bubble profile method at harmonic bubble surface area oscillations. The theoretical approach employed for data analysis was the same as for the dynamic surface tension behavior. Again, satisfactory agreement between the experimental data and theoretical calculations of the dilational rheological parameters was found.

Possible Existence of Convective Currents in Surfactant Bulk Solution in Experimental Pendant-Bubble Dynamic Surface Tension Measurements

Traditionally, surfactant bulk solutions in which dynamic surface tension (DST) measurements are conducted using the pendant-bubble apparatus are assumed to be quiescent. Consequently, the transport of surfactant molecules in the bulk solution is often modeled as being purely diffusive when analyzing the experimental pendant-bubble DST data. In this Article, we analyze the experimental pendant-bubble DST data of the alkyl poly (ethylene oxide) nonionic surfactants, C12E4 and C12E6, and demonstrate that both surfactants exhibit "superdiffusive" adsorption kinetics behavior with characteristics that challenge the traditional assumption of a quiescent surfactant bulk solution. In other words, the observed superdiffusive adsorption behavior points to the possible existence of convection currents in the surfactant bulk solution. The analysis presented here involves the following steps: (1) constructing an adsorption kinetics model that corresponds to the fastest rate at which surfactant molecules adsorb onto the actual pendant-bubble surface from a quiescent solution, (2) predicting the DST behaviors of C12E4 and C12E6 at several surfactant bulk solution concentrations using the model constructed in step 1, and (3) comparing the predicted DST profiles with the experimental DST profiles. This comparison reveals systematic deviations for both C12E4 and C12E6 with the following characteristics: (a) the experimental DST profiles exhibit adsorption kinetics behavior, which is faster than the predicted fastest rate of surfactant adsorption from a quiescent surfactant bulk solution at time scales greater than 100 s, and (b) the experimental DST profiles and the predicted DST behaviors approach the same equilibrium surface tension values. Characteristic (b) indicates that the cause of the observed systematic deviations may be associated with the adsorption kinetics mechanism adopted in the model used rather than with the equilibrium behavior. Characteristic (a) indicates that the actual surfactant bulk solution in which the DST measurement was conducted, most likely, cannot be considered to be quiescent at time scales greater than 100 s. Accordingly, the observed superdiffusive adsorption behavior is interpreted as resulting from convection currents present in a nonquiescent surfactant bulk solution. Convection currents accelerate the surfactant adsorption process by increasing the rate of surfactant transport in the bulk solution. The systematic nature of the deviations observed between the predicted DST profiles and the experimental DST behavior for C12E4 and C12E6 suggests that the nonquiescent nature of the surfactant bulk solution may be intrinsic to the experimental pendant-bubble DST measurement approach. To validate this possibility, we identified generic features in the experimental DST data when DST measurements are conducted in a nonquiescent surfactant bulk solution, and the DST measurements are analyzed assuming that the surfactant bulk solution is quiescent. An examination of the DST literature reveals that these identified generic features are quite general and are observed in the experimental DST data of several other surfactants (decanol, nonanol, C10E8, C14E8, C12E8, and C10E4) measured using the pendant-bubble apparatus.

Dynamic Surface Tension Behavior in a Photoresponsive Surfactant System

The surface properties of a nonionic photoresponsive surfactant that incorporates the light-sensitive azobenzene group into its tail have been investigated. Cis-trans photoisomerization of this azobenzene group alters the ability of the surfactant to pack into adsorbed monolayers at an air/water interface or into aggregates in solution, thereby causing a significant variation in surface and bulk properties following a change in the illumination conditions. NMR studies indicate that a solution left in the dark for an extended period of time contains the trans isomer almost exclusively, whereas samples exposed to light of fixed wavelength eventually reach a photostationary equilibrium in which significant amounts of both isomers are present. At concentrations well above the cmc but under different illumination conditions (dark, UV light, visible light), freshly formed surfaces exhibit profoundly different surface tension trajectories as they approach essentially identical equilibrium states. This common equilibrium state corresponds to a surface saturated with the trans (more surface active) isomer. The dark sample shows a simple, single-step relaxation in surface tension after the creation of a fresh interface, whereas the UV and visible samples exhibit a more rapid initial decrease in tension, followed by a plateau of nearly constant tension, and finally end with a second relaxation to equilibrium. It is hypothesized that this behavior of the UV and visible samples is caused by competitive adsorption between the cis and trans isomers present in these mixtures. The cis surfactant reaches the interface more quickly, leading to an initially cis-dominated interface having a tension value corresponding to the intermediate plateau, but is ultimately displaced by the trans isomer. Fluorescence studies are used for cmc determination in the samples, and the results suggest that the two isomers segregate into distinct aggregate phases. The critical concentration associated with the formation of cis-rich aggregates is much larger than that of the trans-rich aggregates, which accounts for the faster diffusion of the cis isomer to a fresh interface. Models of the diffusion and adsorption of surfactant are developed. These consider the role of aggregates in the adsorption process by examining the limiting behavior of three aggregate properties: dissolution rate, mobility, and ability to incorporate into the interface. These models are used to analyze the surface tension relaxation of dark and UV samples, and the predictions are found to be in agreement with the observed characteristic relaxation time scales for these samples, though the results are inconclusive regarding the specific role of aggregates. High-intensity illumination focused on a surface saturated with surfactant is used to drive photoisomerization of the adsorbed surfactant, and rapid, substantial changes in surface tension result. These changes are consistent with proposed conformations of the adsorbed surfactant and with monolayer studies performed with a Langmuir film balance.

A model for simulating the dynamic surface tension behavior of aqueous surfactant dispersions

A dynamic adsorption model for surface-active materials at air/liquid interfaces with the consideration of aggregate dissolution effect was developed to investigate the dynamic surface tension behavior of aqueous surfactant dispersions. Two catanionic surfactants, cetylpyridinium dodecylsulfate (CP-DS) and dodecyltrimethylammonium dodecylsulfate (DTMA-DS), with low critical aggregation concentrations were chosen as model systems. Dynamic surface tensions of aqueous CP-DS and DTMA-DS systems were measured by a drop volume tensiometer. A model with diffusion-controlled or mixed-kinetic dynamic adsorption mechanisms considering the dissolution effect of dispersed aggregates was developed to simulate the dynamic surface tension data. An analysis by comparing the model predictions with experimental data demonstrated that the dynamic surface tension behavior of aqueous CP-DS and DTMA-DS dispersions could be described with a diffusion-controlled dynamic adsorption model taking the aggregate dissolution effect into account.

Effect of surface-active agents on the phase holdups of three-phase fluidized beds

Experiments were performed at ambient temperature and pressure in a 127-mm inner diameter column with air, 1.2 and 5-mm spherical glass beads and various aqueous solutions containing surface-active agents. Perforated plates were employed as the gas and liquid distributors. Gas and liquid velocities were chosen to span the dispersed and coalesced bubble flow regimes. The dynamic surface tension behaviour of a specific liquid solution correlated to its ability to form stable foam. However, the magnitude of the impact of surface-active agents on phase holdups depended primarily on the operating conditions. The presence of surface-active agents increased the gas holdups in a bubble column by an average of 41%. In a three-phase fluidized bed, surface-active agents increased the gas holdups by an average of 37% while the liquid and solids holdups were reduced by an average of 6.2 and 4.5%, respectively. There is still no reliable means to estimate the gas holdups of three-phase fluidized beds subject to foaming. More work is required to quantify the interaction effects of surface-active agents and operating conditions on the hydrodynamic features of multiphase reactors.

Short-time behavior of mixed diffusion-barrier controlled adsorption

This paper focuses on the short-time adsorption kinetics of nonionic surfactants onto water/air surfaces, analyzed in the context of the mixed diffusion-barrier controlled adsorption modeling framework. Specifically, we reconcile the apparent contradiction between theoretical prediction and experimental observations on the adsorption kinetics mechanism at short times: while the mixed diffusion-barrier controlled model predicts a barrier-controlled adsorption, as well as the impossibility of a diffusion-controlled adsorption at asymptotic short times, the short-time experimental dynamic surface tension (DST) behavior of many nonionic surfactants has been interpreted to result from diffusion-controlled adsorption at asymptotic short times. This is because the short-time experimental DST of these surfactants displays a t variation, which is considered as a fingerprint for the existence of diffusion-controlled adsorption, based on the short-time asymptotic behavior of the diffusion-controlled adsorption model. As a result of this interpretation, the fundamental physical nature of the energy barrier has been proposed to be associated with high surfactant surface concentrations. In this paper, we derive a new nonasymptotic short-time formalism of the mixed diffusion-barrier controlled model to describe surfactant adsorption onto a spherical pendant-bubble surface, including determining the ranges of time and surfactant surface concentration values where the short-time formalism is applicable. Based on this formalism, we find that one can expect to observe an apparent t variation of the DST at short times even for the mixed diffusion-barrier controlled adsorption model. We analyze the consequence of this finding by re-evaluating the existing notions of the energy barrier. We conclude that the energy barrier is associated with the adsorption of a single surfactant molecule onto a clean surface.

Interfacial properties and foam stability effect of novel gemini-type surfactants in aqueous solutions

Static and dynamic surface tension and interfacial rheological behavior of a novel anionic gemini-type surfactant without a spacer group, sodium 2,3-didodecyl-1,2,3,4-butane tetracarboxylate (GS), were investigated. Very low values for critical micelle concentration ( 8.9 × 10 −5 M ) as well as equilibrium surface tension (22.7 mN m −1) were observed for the aqueous solutions. Dynamic surface tension (DST) is very slow and less sensitive to the surfactant concentration than the conventional monomeric surfactant, suggesting the presence of a significant adsorption barrier for GS owing to a complicated molecular structure. Presence of a small concentration of GS in sodium dodecyl sulfate (SDS) solution shows a synergistic effect to form mixed micelles and lowers the cmc considerably. This synergism between GS and SDS and slow exchange of GS between bulk and interface create a rigid air–liquid interface of the SDS–GS solution, which is reflected in a higher elasticity value for the interface of the SDS–GS solution than for the SDS solution. It has been found that the presence of a small concentration of GS in SDS solution increases the foam stability noticeably. Although the stability of the wet foam is correlated with the film elasticity, the stability of dry foam cannot be explained in terms of film elasticity alone.