Surface Dilational Viscoelasticity Research Articles

Gas-liquid surface characterization and liquid film thinning of Non-Aqueous foam

Foam flooding is a crucial enhanced oil recovery technique for profile control during the oil displacement process. The stability of the foam is the key factor for the success of foam flooding, but typical aqueous foams generally lose their stability in the presence of hydrocarbons because of their low oil tolerance. Non-aqueous foams could possess outstanding stability in the presence of hydrocarbons as a result of their unique properties. However, few studies have been conducted on the stabilization mechanisms of non-aqueous foams in the presence of hydrocarbons. In this study, comparative experiments are performed to investigate differences in the stabilization mechanism between aqueous and non-aqueous foams. The results show that a non-aqueous foam had excellent oil tolerance in a bulk foaming test. Then, the stabilization mechanisms of foams are investigated in terms of surface dilatational viscoelasticity and liquid film thinning. For a non-aqueous foam system, the maximum viscoelastic modulus of 55 mN/m occurs at the maximum surfactant concentration used which was 5.0 wt% for this set of tests, which indicates that the liquid film of FS22 non-aqueous foam was more stable. In a foam film thinning experiment, the thinning time of an aqueous foam system is shortened but the liquid film thickness is increased by crude oil, whereas crude oil increased the thinning time of a non-aqueous foam system but decreased its liquid film thickness. In a non-aqueous foam system, the film could remain stable for hours before rupturing, which indicates that its stability in the presence of an oil phase is excellent. These results are meaningful for the understanding of the stabilization mechanisms of oil-based foams and the employment of non-aqueous foams for enhanced oil recovery.

Amphiphilic block copolymers as dual flocculation-flotation agents for rapid solid–liquid separation of radioactive wastes

The potential of poly(acrylic acid)-b-poly(n-butyl acrylate) as a dual flocculant-collector in combined flotation-sedimentation dewatering operations was investigated. The amphiphilic block copolymers were synthesised with consistent hydrophilic chain lengths and varying hydrophobic chain lengths. Various techniques were employed to analyse polymer behaviour at the air–water interface, being interfacial surface tension and dilational viscoelasticity. Polymer adsorption onto Mg(OH)2 was determined differentially using UV–Vis spectroscopy. Floc structures were determined using static light scattering, and flocculation-flotation performance was analysed using settling tests and flotation cell material balances. Results showed that longer hydrophobic chains were less surface-active, reducing foamability and water entrainment. The unimer-micellar adsorption transition points were identified through viscoelastic properties and particle adsorption studies. A distinct change in floc density and structure was observed for the largest molecular weight copolymer when the dosed concentration increased into the micellar adsorption region, suggesting a pseudo-bridging flocculation mechanism. Settling rates were significantly higher for particles flocculated with the larger molecular weight polymer, correlating to their larger aggregate sizes, especially over the micellar transition point. The largest molecular weight block copolymer demonstrated superior collection efficiency compared to the traditional surfactant, sodium dodecylsulfate (SDS), below its micellar adsorption transition point. However, beyond this point, the lack of exposed hydrophobic blocks hindered the hydrophobisation of Mg(OH)2 particles, reducing collection efficiency. Comparing flotation cell particle size distributions, it was suggested that recovery may be hydrodynamically hindered by the largest floc sizes, though recovery was observed for particles in the order of < 600 μm.

Effect of Surface Freezing of a Cationic Surfactant and n-Alkane Mixed Adsorbed Film on Counterion Distribution and Surface Dilational Viscoelasticity Studied by Total Reflection XAFS and Surface Quasi-Elastic Light Scattering.

When liquid alkane droplets are placed on a surfactant solution surface having a proper surface density, alkane molecules penetrated into the surfactant-adsorbed film to form a mixed monolayer. Such a mixed monolayer undergoes a thermal phase transition from two-dimensional liquid to solid monolayers upon cooling when surfactant tail and alkane have similar chain lengths. We applied the total-reflection XAFS spectroscopy and surface quasi-elastic light scattering to the mixed adsorbed film of cetyltrimethylammonium bromide and hexadecane to elucidate the impact on the surface phase transition on the counterion distribution of the mixed monolayer. The EXAFS analysis verified that a higher percentage of counter Br- ions were localized in the Stern layer than in the diffuse double layer in the surface solid film compared to the surface liquid film, which resulted in a reduction in the surface elasticity measured by the SQELS. The finding that the surface phase transition accompanies the change in the counterion distribution will be important to consider the future applications of the colloidal systems, in which the coexistence of a surfactant and alkane molecules is essential, such as foams and emulsions.

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.

Investigation on the Stability of Janus SiO2-n Nanoparticle-Assisted Nonionic Surfactant-Stabilized Foam and Its Application in Enhanced Oil Recovery

The stability of the foam directly impacts the final efficiency of the foam flooding in enhanced oil recovery (EOR). In the present work, a series of Janus SiO2-n nanoparticles (JSn NPs) with various modification degrees were successfully prepared and employed to improve the stability of the nonionic surfactant polyethylene glycolmonoisodecylether (PMIE)-stabilized foam. The PMIE–JS3 system with a much low JS3 NP concentration (0.1 wt %) displayed extraordinary foamability and stabilizing foam ability via the foam volume, half-life, relative volume decay, and optical microscope photograph measurements. Then, the dynamic surface tension and dilatational viscoelasticity tests were conducted to explore the mechanism. It was found that the PMIE–JS3 system with great interfacial activity and intensive interfacial film highly facilitated the generation of the foam and improved the foam stability. Moreover, the PMIE–JS3-stabilized foam exhibited outstanding stability, even under the influence of crude oil. The sandpack flooding tests indicated that the PMIE–JS3-stabilized foam could effectively plug the high-permeability channels to modify the water injection profile and consequently greatly enhanced tertiary oil recovery (∼15.3% of the initial oil in place).

Effect of Divalent and Monovalent Salts on Interfacial Dilational Rheology of Sodium Dodecylbenzene Sulfonate Solutions

This study presents the equilibrium surface tension (ST), critical micelle concentration (CMC) and the dilational viscoelasticity of sodium dodecylbenzene sulfonate (SDBS)-adsorbed layers in the presence of NaCl, KCl, LiCl, CaCl2 and MgCl2 at 0.001–0.1 M salt concentration. The ST and surface dilational viscoelasticity were determined using bubble-shape analysis technique. To capture the complete profile of dilational viscoelastic properties of SDBS-adsorbed layers, experiments were conducted within a wide range of SDBS concentrations at a fixed oscillating frequency of 0.01 Hz. Salts were found to lower the ST and induce micellar formation at all concentrations. However, the addition of salts increased dilational viscoelastic modulus only at a certain range of SDBS concentration (below 0.01–0.02 mM SDBS). Above this concentration range, salts decreased dilational viscoelasticity due to the domination of the induced molecular exchange dampening the ST gradient. The dilational viscoelasticity of the salts of interest were in the order CaCl2 &gt; MgCl2 &gt; KCl &gt; NaCl &gt; LiCl. The charge density of ions was found as the corresponding factor for the higher impact of divalent ions compared to monovalent ions, while the impact of monovalent ions was assigned to the degree of matching in water affinities, and thereby the tendency for ion-pairing between SDBS head groups and monovalent ions.

A Multistate Adsorption Model for the Characterization of C13DMPO Adsorption Layers at the Aqueous Solution/Air Interface.

Experimental data for tridecyl dimethyl phosphine oxide (C13DMPO) adsorption layers at the water/air interface, including equilibrium surface tension and surface dilational viscoelasticity, are measured by bubble and drop profile analysis tensiometry at different solution concentrations and surface area oscillation frequencies. The results are used to assess the applicability of a multistate model with more than two possible adsorption states. For the experiments with single drops, the depletion of surfactant molecules due to adsorption at the drop surface is taken into account. For the assessment, the same set of model parameters is used for the description of all obtained experimental dependencies. The agreement between the proposed model and the experimental data shows that for the nonionic surfactant C13DMPO, the description of the adsorption layer behavior by three adsorption states is superior to that with only two adsorption states.

A natural source of saponin: Comprehensive study on interfacial properties of Chubak (Acanthophyllum Glandulosum) root extract and related saponins

Chubak (Acanthophyllum Caryophyllaceae) is a shrubby plant with saponin-rich roots. This feature makes this plant to a new source of natural surfactant. This article presents some basic information about the surface activity of Chubak root extract (CRE) and the corresponding purified saponin. The Calendasaponin B and Calendasaponin D were characterized in the purified saponin using Liquid Chromatography-Mass Spectrometry as the two main saponins. The dynamic surface tension and dilational surface visco-elasticity of CRE and the purified saponin were studied using a profile analysis tensiometer. The equilibrium surface tensions of CRE and the purified saponin in the concentration range up to the CMC show that the used purification method is not efficient to separate the complete saponin content of CRE. The surface activity of CRE started at 0.005 g/l, while the minimum saponin concentration for a first visible surface tension decrease was 0.0012 g/l. The uniform trend in surface dilational elasticity and viscosity of CRE and the purified saponin is the evidence for the similarity of dominant surface-active compounds in both samples. Comparing the short time surface tension of oscillating and steady drops showed the impact of adsorption layer oscillations on the surface tension variations.

A Multistate Adsorption Model for the Adsorption of C14EO4 and C14EO8 at the Solution/Air Interface

The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (CnEOm) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously surfactants that can adsorb in more than two possible conformations. The experimental data for C14EO4 and C14EO8 (dynamic and equilibrium surface tensions and surface dilational visco-elasticity as measured by bubble profile analysis tensiometry) are used to verify if a reorientation model with more than two possible adsorption states can better describe the complete set data of CnEOm adsorption layers at the water/air interface. The proposed refined theoretical model allows s different states of the adsorbing molecules at the interface. The comparison between the model and experiment demonstrates that, for C14EO4, the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C14EO8, a number of s = 10 adsorption states allows an optimum data description.

Thermodynamics, Kinetics and Dilational Visco-Elasticity of Adsorbed CnEOm Layers at the Aqueous Solution/Air Interface

The adsorption behaviour of linear poly(oxyethylene) alkyl ether (CnEOm) is best described by a reorientation model. Based on a complete set of experimental data, including the adsorption kinetics, the equilibrium surface tension isotherm and the surface dilational visco-elasticity, the thermodynamic and kinetic adsorption parameters for some CnEOm at the water/air interface were determined. For the study, six CnEOm surfactants were selected (n = 10, 12 and 14 and m = 4, 5 and 8) and were studied by bubble profile analysis and maximum bubble pressure tensiometry. A refined theoretical model based on a reorientation-adsorption model combined with a diffusion-controlled adsorption kinetics and exchange of matter allowed us to calculate the surface layer composition by adsorbing molecules in different orientations. It turns out that at larger surface coverage, the adsorption rate decreases, i.e., the apparent diffusion coefficients are smaller. This deceleration can be explained by the transition of molecules adsorbed in a state of larger molar surface area into a state with smaller molar surface area.

β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH

The theoretical description of the adsorption of proteins at liquid/fluid interfaces suffers from the inapplicability of classical formalisms, which soundly calls for the development of more complicated adsorption models. A Frumkin-type thermodynamic 2-d solution model that accounts for nonidealities of interface enthalpy and entropy was proposed about two decades ago and has been continuously developed in the course of comparisons with experimental data. In a previous paper we investigated the adsorption of the globular protein β-lactoglobulin at the water/air interface and used such a model to analyze the experimental isotherms of the surface pressure, Π(c), and the frequency-, f-, dependent surface dilational viscoelasticity modulus, E(c)f, in a wide range of protein concentrations, c, and at pH 7. However, the best fit between theory and experiment proposed in that paper appeared incompatible with new data on the surface excess, Γ, obtained from direct measurements with neutron reflectometry. Therefore, in this work, the same model is simultaneously applied to a larger set of experimental dependences, e.g., Π(c), Γ(c), E(Π)f, etc., with E-values measured strictly in the linear viscoelasticity regime. Despite this ambitious complication, a best global fit was elaborated using a single set of parameter values, which well describes all experimental dependencies, thus corroborating the validity of the chosen thermodynamic model. Furthermore, we applied the model in the same manner to experimental results obtained at pH 3 and pH 5 in order to explain the well-pronounced effect of pH on the interfacial behavior of β-lactoglobulin. The results revealed that the propensity of β-lactoglobulin globules to unfold upon adsorption and stretch at the interface decreases in the order pH 3 &gt; pH 7 &gt; pH 5, i.e., with decreasing protein net charge. Finally, we discuss advantages and limitations in the current state of the model.

Dynamics of Competitive Adsorption of Lipase and Ionic Surfactants at the Water-Air Interface.

Lipase is one of the most important enzymes playing a key role in many biological and chemical processes, in particular for fat hydrolysis in living systems and technological applications such as food production, medicine, and biodiesel production. As lipase is soluble in water, the major hydrolysis process occurs at the water-oil interface, where lipase can get in contact with the oil. To provide optimum conditions, the emulsification of the oil is essential to provide a large interfacial area which is generally done by adding surfactants. However, the presence of surfactants can influence the lipase activity and also cause competitive adsorption, resulting in a removal of lipase from the interface or its conformational changes in the solution bulk. Here we have studied the dynamics of competitive adsorption and interfacial elasticity of mixed solutions containing lipase and the anionic surfactant sodium dodecyl sulfate (SDS) or the cationic surfactant cetyltrimethylammonium bromide (CTAB), respectively, at the water-air interface. The experiments were performed with a special coaxial double capillary setup for drop bulk-interface exchange developed for the drop profile analysis tensiometer PAT with two protocols: sequential and simultaneous adsorption of single components and mixed systems. The results in terms of dynamic surface tension and dilational viscoelasticity illustrate fast and complete desorption of a preadsorbed CTAB and SDS layers via subphase exchange with a buffer solution. In contrast, the preadsorbed lipase layer cannot be removed either by SDS or CTAB from the interface during drop bulk exchange with a buffer solution due to the unfolding process and conformation evolution of the protein molecules at the interface. In the opposite case, lipase can remove preadsorbed SDS and CTAB. The dynamic surface tension and viscoelasticity data measured before and after subphase exchange show joint adsorption of lipase and CTAB in the form of complexes, while SDS is adsorbed in competition with lipase. The results are in good correlation with the determined surface charges of the lipase gained by computational simulations which show a dominant negatively charged surface for lipase that can interact with the cationic CTAB while partial positively charged regions are observed for the interaction with the anionic SDS.

Surface tension and dilational rheology of mixed β-casein – β-lactoglobulin aqueous solutions at the water/air interface

Bubble profile analysis tensiometry was used to study the surface tension and dilational visco-elasticity of individual and mixed solutions of β-casein (BCS) and β-lactoglobulin (BLG) at various mixing ratios of the components. The results for the individual protein solutions were analysed based on a new theory, which is applicable in the pre-critical and post-critical concentration range of the surface tension isotherm. It is shown that these proteins are capable of displacing each other from the adsorption layer, which affects the surface tension and visco-elasticity modulus of the adsorbed layers. The model developed for protein mixtures agrees well with the experimental data and the calculated dependencies of the surface properties on the solution composition confirm the mutual influence of added proteins.

Surface Tension and Dilatational Rheology of Blood in Patients Subjected to Cardiological Operations under Conditions of Artificial Circulation

Pendant drop and bubble shape methods are employed to study the tensiometric and rheological parameters of blood serum and plasma in 45 patients 49–70 years old subjected to surgical operations under the conditions of artificial circulation because of ischemic heart disease (first group) and heart valve pathology (second group). Blood sampling is performed 1 h before and 12 h after (the first day) the operation, as well as on the 7th postoperative day. Statistically significant changes in the surface tension and viscoelasticity modulus are observed on the 1st day after the operation in both groups, thereby indicating a substantial increase in the content of surfactants in the blood serum. On the seventh day of the postoperative period, a positive dynamics is observed; however, the studied rheological parameters—in particular, viscoelasticity modulus E—at frequencies of 0.1 and 0.01 Hz statistically reliably exceed their preoperative level and do not reach the values characteristic of healthy people. Thus, the pathological deviations of biochemical parameters (contents of glucose, urea, creatinine, albumin, and lipoproteins) that affect blood viscosity are accompanied by substantial changes in the surface tension and dilatational viscoelasticity of blood serum. However, the examined biochemical markers are not dominating predictors for changes in the rheological and tensiometric properties of blood.

ПОВЕРХНОСТНОЕ НАТЯЖЕНИЕ И ДИЛАТАЦИОННАЯ ВЯЗКОУПРУГОСТЬ СЫВОРОТКИ КРОВИ У ПАЦИЕНТОВ ОПЕРИРОВАННЫХ НА СЕРДЦЕ В УСЛОВИЯХ ИСКУССТВЕННОГО КРОВООБРАЩЕНИЯ

Цель работы. Установить значения показателей поверхностного натяжения и дилатационной вязкоупругости:1. стандартно применяемых растворов для первичного заполнения контура ИК;2. сыворотки крови у пациентов, оперированных на сердце в условиях ИК в пери- и интраоперационных периодах.Материал и методы. Проведено проспективное исследование поверхностного натяжения и дилатационной вязкоупругости сыворотки у 16 пациентов в возрасте 62,1±0,9 года, оперированных в условиях искусственного кровообращения. Забор проб производился за 1 час до операции, на 5-й минуте ИК и через 12 часов после операции. Также определяли: уровень глюкозы, общего белка, гемоглобина и гематокрита. При проведении тензиометрических исследований сыворотки крови во время ИК отдельно были исследованы следующие растворы: маннитол 15%, гелофузин и альбумин 10%.Результаты и обсуждение. Обращает на себя внимание аномальная зависимость динамического поверхностного натяжения γ, 100с от размера (и молекулярной массы) изучаемых веществ. Непосредственно после начального формирования капли в экспериментальной установке поверхностное натяжение растворов белков и других крупных молекул близко к поверхностному натяжению воды вследствие диффузионного контроля процесса. В нашем случае наблюдается прямо противоположная картина: чем выше молекулярная масса исследуемого компонента, тем меньше γ, 100 с.Результаты исследования тензиометрических и дилатационных вязкоупругих свойств сыворотки крови у всех групп больных статистически значимо отличаются от контрольной группы. В то же время γ,100с практически не отличается между группами больных, даже во время ИК, что говорит, видимо, о наличии низкомолекулярых ПАВ в сыворотке крови больных. Сходная картина наблюдается и для равновесного поверхностного натяжения: статистически неразличимые по этому параметру группы больных достоверно отличаются от контроля.Выводы. Изменения значений параметров поверхностного натяжения и дилатационной вязкоупругости сыворотки крови сопровождаются патологическими отклонениями со стороны биохимических показателей крови. Однако определяемые биохимические маркеры не являются доминирующими предикторами в изменении рео- и тензиометрических свойств крови.

β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 3. Neutron Reflectometry Study on the Effect of pH.

Several characteristics of β-lactoglobulin (BLG) layers adsorbed at the air/water interface exhibit a strong pH dependence, but our knowledge on the underlying structure-property relations is still fragmental. Here, we therefore extend our recent studies by neutron reflectometry (NR) and provide a comprehensive overview through direct measurements of the surface excess Γ and the layers' molecular structure. This enables comparison with available literature data to draw general conclusions. The NR experiments were performed at various pH values and within a wide range of protein concentrations, CBLG. Adsorption kinetics measurements in air-contrast-matched-water and over a narrow Qz range enabled direct quantification of the dynamic surface excess Γ(t) and are found to be consistent with ellipsometry data. Near the isoelectric point, pI, the rates of adsorption and Γ are maximal but only at sufficiently high CBLG. NR data collected over a wider Qz range and in two aqueous isotopic contrasts revealed the structure of adsorbed BLG layers at a steady state close to equilibrium. Independent of the pH, BLG was found to form dense monolayers with average thicknesses of 1.1 nm, suggesting flattening of the BLG globules upon adsorption as compared with their bulk dimensions (≈3.5 nm). Near pI and at sufficiently high CBLG, a thick (≈5.5 nm) but looser secondary sublayer is additionally formed adjacent to the dense primary monolayer. The thickness of this sublayer can be interpreted in terms of disordered BLG dimers. The results obtained and notably the specific interfacial structuring of BLG near pI complement previous observations relating the impact of solution pH and CBLG on other interfacial characteristics such as surface pressure and surface dilational viscoelasticity modulus.

Relaxation Behavior and Nonlinear Surface Rheology of PEO-PPO-PEO Triblock Copolymers at the Air-Water Interface.

Surface dilatational viscoelasticity of adsorbed layers of pluronics triblock copolymers at the air-water interface was measured using the oscillating barrier technique. The effect of molecular architecture and concentration on surface viscoelasticity was explored for two different types of pluronics with different degrees of hydrophobicity, Pluronic F-108 (Mw ≈ 14 600 g/mol) and Pluronic P-123 (Mw ≈ 5800 g/mol), the former exhibiting a larger hydrophilic to hydrophobic block length ratio. Frequency sweeps in the linear regime suggested that interfacial films of F-108 have higher surface limiting elasticity and larger in-plane and out-of-plane relaxation times at the same bulk concentration (the former possibly related to in-plane microstructure rearrangements, the latter to surface/bulk diffusion). Increasing the bulk concentration of pluronics from 1 to 100 μM led to a decrease in both in- and out-of-plane relaxation times. Large amplitude oscillatory dilatation (LAOD) tests were performed to capture nonlinear behavior of these interfacial films by means of elastic and viscous Lissajous plots. Nonlinearities in elastic responses were quantified through calculation of the strain-stiffening indices in extension SE and compression SC. Both pluronics exhibited strain softening in extension. In compression, P-123 showed strain-hardening and F-108 displayed a relatively linear response. Apparent strain hardening in extension was observed for the P-123 adsorbed film, at high strain, at a bulk concentration of 100 μM. However, at these strains, the response was dominated by the viscous contribution and calculation of strain rate-thickening factors in extension and compression showed that the overall response was strain rate-thinning in extension and strain rate-thickening in compression.

Characterisation of egg white adsorption layers under equilibrium and dynamic conditions

The rheological properties of egg white adsorbed layer at pH 9 and 7 at air/water interface is investigated in a wide range of dilute to reconstructed egg white solution using pendant drop tensiometer. The aggregation of proteins in the solution bulk influences the adsorption behavior as well as the dilational visco-elasticity (measured at various frequencies) of adsorbed layer. The comparison of the dilational visco-elasticity as measured at equilibrium and under dynamic conditions shows pH effects of the egg white molecules. Furthermore, the formation of dynamic adsorption layers of egg white proteins at the surface of rising bubbles was investigated by measuring the local rising velocity at low protein concentrations at pH 9 and 7. The velocity profiles of the rising bubble were in agreement with the dynamic surface tension and dilational visco-elasticity results. The time required to establish the adsorption layers of egg white at pH 7 is shorter than at pH 9 due to the conformation of the protein molecules close to the isoelectric point.

Effect of Amplitude on the Surface Dilational Visco-Elasticity of Protein Solutions

Harmonic drop surface area oscillations are performed at a fixed frequency (0.1 Hz) to measure the dilational visco-elasticity for three proteins: β-casein (BCS), β-lactoglobulin (BLG), and human serum albumin (HSA). The surface area oscillations were performed with different amplitudes in order to find the origin of non-linearity effects. The analysis of data shows that the non-linearity in the equation of state—i.e., the relation between surface pressure and surface concentration of adsorbed protein molecules—is the main source of the amplitude effects on the apparent visco-elasticity, while perturbations due to non-uniform expansions and compressions of the surface layer, inertia effects leading to deviations of the drop profile from the Laplacian shape, or convective transport in the drop bulk are of less importance. While for the globular proteins, HSA and BLG the amplitude effects on the apparent visco-elasticity are rather large, for the non-globular protein BCS this effect is negligible in the studied range of up to 10% area deformation.

Effects of Sodium Benzoate and Sodium Chloride on the Aggregation Behaviors of PEO‐PPO‐ph‐PPO‐PEO and PPO‐PEO‐ph‐PEO‐PPO at the Air/Water Interface

AbstractThe effect of sodium benzoate and sodium chloride on the aggregation behavior of PEO‐PPO‐ph‐PPO‐PEO (BPE) and PPO‐PEO‐ph‐PEO‐PPO (BEP) polyethers at the air/water interface was investigated by measuring the equilibrium surface tension, surface dilational viscoelasticity, and surface tension relaxation. The measurements of surface tension showed that sodium benzoate has a better effect on decreasing the surface tension of BPE and BEP solutions than NaCl, especially when the polyether concentrations are low. According to dilational viscoelasticity measurements, the concentration of BPE required for the maximum dilational modulus is lower than that of BEP, indicating that BPE more easily forms a compact adsorbed layer. The dilational modulus values of BPE solutions in the presence of sodium benzoate and NaCl first increase and then decrease after passing through a maximum, and then they increase again with increasing electrolyte concentration. On the other hand, the dilational modulus values of BEP solutions in the presence of sodium benzoate and NaCl first increase to a maximum and then decrease with increasing electrolyte concentration. The surface tension relaxation results are consistent with those of dilational viscoelasticity. The different effects of sodium benzoate and NaCl on the polyether aggregation behaviors are caused by the strong hydrophobic and π‐π interactions between polyethers and sodium benzoate. This work has a great importance for the application and development of polyethers.