Surface Dilational Properties Research Articles

Interfacial moduli at large strains and stability of emulsions stabilised by plant proteins at high bulk shear rates

For several commercial plant-protein stabilisers, we investigated how surface shear and dilatational properties affect dynamic emulsion stability under high bulk shear conditions. Potato protein isolates Potato-1 (rich in patatin) and Potato-2 (rich in protease inhibitors) showed a stiffer, more solid-like response than soy and pea protein isolates in large amplitude oscillatory surface shear. Soy protein isolates had the weakest interfaces and showed a more liquid-like behaviour. Potato-2 had the highest stiffness and most brittle interface in large amplitude oscillatory dilatational deformations. It also showed more significant softening, evident from both the shear and dilatational Lissajous plots. Only the Potato-1-stabilised emulsion was stable against coalescence at high bulk shear (although that emulsion was unstable against flocculation because of its low zeta potential). The low stiffness imparted to the interface by the pea and soy protein isolates was not suitable for preparing emulsions with high dynamic stability. In the linear regime, both Potato-1 and Potato-2 produced interfaces with similar surface shear moduli, and in dilatation, Potato-2 gave a higher modulus. The lower stability of the Potato-2 emulsions appears to be linked to the higher brittleness and stronger softening effect for increasing deformation amplitude. Both in surface shear and dilatation, the maximum linear strain for the Potato-1-stabilised interface is larger. The lower maximum linear strain and stronger softening effect at high deformations for Potato-2 may have resulted in more disruption of the interfacial microstructure, and this induced (partial) coalescence.

Surface dilatational and foaming properties of whey protein and escin mixtures

Saponins are naturally occurring components in plants, which have promising interface stabilising properties. In this work, we will focus on the saponin type called escin, which is known to form very strong viscoelastic interfacial layers at the air-water interface. The ability to form stiff interfaces can be advantageous for stabilising foams. The interfacial properties of escin were studied in mixtures with whey protein isolate (WPI). Understanding multicomponent systems is crucial in designing food products, containing both proteins and saponins. Pure WPI and escin, and WPI-escin mixtures at 7:1, 3:1, 1:1, and 1:3 (w:w, WPI:escin) ratio were evaluated for their interfacial properties using large amplitude oscillatory dilatation (LAOD). The responses to the deformations were highly non-linear and could only be assessed by plotting Lissajous plots of the surface stress signal versus deformation. Escin appeared to co-adsorb with WPI, leading to mixed interfaces. A small addition of escin, such as in the 7:1 or 3:1 (WPI:escin) ratios, already resulted in substantially stiffer interfacial layers compared to pure WPI. At higher escin content (1:1 and 1:3), escin completely dictated the mechanical properties of the interfaces, which resulted in stiff and glassy-like systems. The stiff interfacial layers of escin resulted in about three times more stable foams compared to pure WPI. We also observed higher foam stability for mixtures with higher escin contents. Escin is a promising natural and plant-based foaming ingredient, which can be mixed with whey proteins to create stable aerated systems.

Effect of electrolyte on the surface dilational rheological properties of branched cationic surfactant

The studies of surface dilational rheology are important to detent the nature of adsorption film and the properties of foam. In this paper, the adsorption and dilational rheological properties of branched cationic surfactant hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC) at the air-water interface in the absence and presence of electrolyte (NaCl) were investigated by drop shape analysis. The results show that the surface adsorption layer of C16G(EO)3PC behaves elastic in nature with high value up to 90 mN/m, which indicates that the slow relaxation process plays a main role because of the re-arrangement of long branched alkyl chain. The addition of NaCl will enhance diffusion-exchange process and accelerate the formation of film and decreases dilational elasticity obviously. At low NaCl concentration, the in-film slow relaxation process dominates the nature of film, dilational viscosity decreases with an increase of oscillating frequency. By adding more NaCl, diffusion-exchange process plays the crucial role and dilational viscosity increase as a function of frequency. Moreover, viscosity at high NaCl concentration shows larger value under higher oscillating frequency, indicating the contributions of fast diffusion-exchange process. The elastic adsorption film becomes to be viscoelastic by adding electrolyte.

Foam Structure Preservation during Microwave-Assisted Vacuum Drying: Significance of Interfacial and Dielectric Properties of the Bulk Phase of Foams from Polysorbate 80-Maltodextrin Dispersions.

This study aimed at examining the cause of differences in the structure preservation of polysorbate 80–maltodextrin foams during microwave-assisted vacuum drying (MWVD) versus conventional vacuum drying (CVD). Aqueous dispersions of 3% polysorbate 80 and 0–40% maltodextrin were characterized for their dielectric and interfacial properties, and results were related to their drying performance in a foamed state. Surface tension and surface dilatational properties as well as dielectric properties clearly responded to the variation in the maltodextrin content. Likewise, the foam structure preservation during CVD was linked to the maltodextrin concentration. Regarding MWVD, however, foams collapsed at all conditions tested. Nevertheless, if the structure during MWVD remained stable, the drying time was significantly reduced. Eventually, this finding could be linked to the dielectric properties of polysorbate 80 rather than its adsorption kinetics and surface film viscoelasticity as its resonant frequency fell within the working frequency of the microwave drying plant.

Influence of interfacial characteristics and dielectric properties on foam structure preservation during microwave-assisted vacuum drying of whey protein isolate-maltodextrin dispersions

This study aimed at assessing the correlation between interfacial and dielectric properties of whey protein isolate (WPI)-maltodextrin (MD) dispersions and their foam structure stability during conventional vacuum drying (CVD) and microwave-assisted vacuum drying (MWVD). Interestingly, the presence of MD clearly increased the surface activity of WPI, whereas the surface dilatational properties were rather unaffected. Besides, loss factor and resonant frequency linearly increased with MD concentration, while the dielectric constant decreased. Regarding drying, foam structure preservation during CVD was mainly correlated with the dilatational elasticity. Thereby, all samples remained stable throughout the drying process. Compared to CVD, MWVD required ≥20% MD to avoid foam collapse. In addition, MWVD-dried samples exhibited larger bubble sizes, which was linked to the volumetric heating and higher mechanical stress as compared to CVD. Overall, high surface dilatational elasticity and bulk viscosity were identified as key parameters to ensure foam structure preservation during vacuum drying. • Maltodextrin content ≥30% affects interfacial properties of WPI. • Dielectric properties of WPI depend on maltodextrin content and temperature. • Foam decay is related to interfacial properties. • Foam structure stability during MWVD is linked to surface elasticity.

Adsorption and viscoelastic properties of chitosan lactate at the liquid-gas interface

The surface tension and dilational rheological properties (viscoelasticity modulus and phase angle) of chitosan lactate solutions at the liquid-gas interface are investigated by the oscillating drop shape method. The results were analyzed using the adsorption model proposed earlier for proteins in the framework of non-ideal two-dimensional solution theory. It was found that the experimental values of equilibrium surface tension of chitosan lactate solutions are in good agreement with this model. The results of the dynamic surface tension and adsorption kinetics analysis showed that chitosan lactate is characterized by a non-diffusion (barrier) adsorption mechanism. This fact determines the qualitative predictive value of the applied theoretical model to describe the extreme behavior of the dependence of the viscoelasticity modulus on the surface pressure.

Surface Dilatational Properties and Foam Performance of Surfactant-Nanoparticle Foaming System under Ultra-High Salinity

Abstract We have studied the surface dilatational properties of aqueous foaming dispersions containing mixtures of silica nanoparticles (Ludox CL) and sulfobetaine (LHSB) in Tahe formation water. The effects of temperature and pH on the surface dilatational modulus and time shift were studied by oscillating drop module (ODM). The ODM results show that the surface dilatational modulus of mixtures of CL and LHSB is large and increases with the decrease of surface area deformation, which results from hydrophobic interaction between adsorbed mixtures. Under test conditions, the Gibbs stability criterion E > σ/2 against foam coarsening is fulfilled. Results of Brewster angle microscopy (BAM) show that an uniform adsorption layer is established at the air-water interface. Temperature and pH-value influence the dilatation modulus of the surface by hydrophobic interaction or adsorption. Time shift has a similar variation trend. This is a surprising feature. It suggests that LHSB adsorbed on CL can respond to surface tension gradient. The time shift difference results from the response of LHSB at different adsorption sites. In addition, sand pack tests show that compared to LHSB, a finer foam was produced by the mixtures CL/LHSB due to the capillary-induced \snap-off". Thus, higher pressure difference and higher oil recovery could be achieved.

Impact of Adsorption Layer Properties on Drainage Behavior of Microscopic Foam Films: The Case of Cationic/Nonionic Surfactant Mixtures

Aqueous mixtures of cationic hexadecyltrimethylammonium chloride (CTAC) and nonionic pentaethyleneglycol monododecyl ether (C12E5) are investigated. Adsorption layer properties are systematically studied within a wide concentration range for a 1:1 molar ratio of the surfactants. Surface tension and dilatational rheology measurements are conducted by profile analysis tensiometry. The interfacial data are juxtaposed to drainage kinetics and stability results for microscopic foam films, investigated by microinterferometric thin liquid film instrumentation. The obtained results give experimental evidence of synergistic interactions in the studied solutions, as compared to the corresponding single surfactant systems. Specific runs of dynamic and equilibrium surface tension curves are registered against the total surfactant quantity; the surface dilatational elasticities for the mixtures are systematically higher. A clear correlation is established between adsorption layer performance and foam film characteristics. The maxima of the film lifetimes are well outlined, and the respective values are shifted towards lower overall concentrations. The reported results substantiate the key role of the adsorption layers, and the surface dilatational properties in particular, for foam film drainage kinetics and stability. The well-expressed synergy observed in adsorption layer and foam film properties suggests the substantial benefits of using mixed surfactant systems in the design and fine-tuning of foam systems for innovative applications.

Surface and foaming properties of potato proteins: Impact of protein concentration, pH value and ionic strength

Using a multiscale approach, potato protein isolate was characterized holistically in terms of its solubility and surface charge, surface activity and surface dilatational properties as well foaming properties and bubble structural attributes. By means of varying protein concentration (0.1–10.0%), pH (3.0–10.0) and NaCl concentration (0–200 mM), it was aimed to establish a better mechanistic understanding of potato protein functionality. Overall, surface activity was found to be rather unaffected by a modification of protein concentration and pH, whereas pH had a clear effect on surface dilatational elasticity. Likewise, foam stability was affected by pH, yielding a maximum around the isoelectric point, which is due to an enhanced network formation at the air/water interface imparting an increased surface film stability. Coarsening exponents were found to reflect the results on foam stability. By comparison, NaCl presence clearly had an enhancing effect on surface activity and led to increased protein-protein interactions within the surface film. More compact surface films in turn resulted in a better foamability and foam stability as well as lower coarsening exponents. Comparison of findings to mechanisms known for β-lactoglobulin-stabilized surfaces revealed their principal applicability also to potato proteins’ functional properties. Overall, by means of the obtained knowledge, foam structures based on potato proteins can be controlled more specifically.

Combining surface dilatational rheology and quantitative proteomics as a tool for understanding microstructures of air/water interfaces stabilized by sodium caseinate/tannic acid complex

A combination method of surface dilatational rheology and quantitative proteomics can be used to investigate the adsorbed proteins on the air/water interface which stabilized by sodium caseinate (SC) or sodium caseinate/tannic acid (SC/TA) complex in this work. First, we explored the change in foam volume with time. Results showed that foam stability (FS) increased with the increasing of bulk concentration of TA. The number of actual aggregates in foam lamella which accounts for improved foam stability was well quantified using optical microscopy and CLSM. Besides, the surface dilatational rheological properties indicated that the formation of the SC/TA complex increased the elastic modulus (Ed) of the air/water interface, which is useful for inhibiting collapse. Finally, adsorbed proteins were obtained by freeze-drying method and proteins were labeled and subjected to reversed-phase high-performance liquid chromatography coupled to tandem mass spectrometry (RPLC-ESI–MS/MS) for protein identification and quantification. The results showed that the significant improvement in the foam stability of the system is due to the addition of TA to increase the amount of κ-casein adsorbed on the interface, resulting in a more elastic air/water interface. The results presented in this study should provide detailed quantitative information of the interfacial layer, and will facilitate the application of the formed protein/polyphenol complex as functional ingredients in food and non-food systems.

Effect of branched chain and polyoxyethylene group on surface dilational rheology of cationic surfactants

The measurements of dynamic surface tensions and surface dilational rheological properties were carried out for four cationic surfactants aqueous solutions, hexadecanol glycidyl ether ammonium chloride (C16PC), guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C16GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride(C16(EO)3PC) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC), using the oscillating bubble method. The influences of surface ageing time, surface pressure, dilational frequency and bulk concentration on surface rheological properties have been expounded. It is found that diffusion-exchange process plays the crucial role for C16PC film at all experimental concentrations. On the other hand, the relaxation process in-surface dominates the properties of film at low and high bulk concentration for branched cationic surfactants and C16(EO)3PC respectively. The branched hydrophobic chain will enhanced the molecular interactions at the surface and improve the value of modulus maximum. The introducing of EO group will produce new relaxation process, such as the variation of orientation of EO group at the surface, which enhances the contributions of viscous nature of film. Moreover, the coexistence of branched chain and EO group will produce oriented variations of film structure and result in the maximum modulus at dynamic curve.

Salt-dependent interaction behavior of β-Lactoglobulin molecules in relation to their surface and foaming properties

This multiscale study aimed at assessing the transferability of bulk phenomena to surface and foaming properties in terms of the establishment of structure-function relationships using the example of β-Lactoglobulin (β-Lg). The impact of salt type and concentration (i.e., NaCl and CaCl2, 0–300 mM) on the interaction behavior of β-Lg molecules in bulk solution (i.e., 0.1%, pH 6.8) firstly was analyzed by means of angular and concentration-dependent static light scattering. Subsequently, surface (i.e., adsorption behavior and surface dilatational properties) and foaming properties (i.e., foam formation and decay behavior including bubble structural characteristics) were investigated. According to the second osmotic virial coefficient, protein-solvent interactions prevailed in presence of NaCl, whereas CaCl2 promoted protein-protein interactions. These differences particularly appeared for salt concentrations < 200 mM. Surface as well as foaming properties of β-Lg were found to respond to changes in salt type and concentration and to reflect salt-specific effects. In particular, β-Lg adsorption at the air/water interface and foam formation were enhanced, whereby the influence of CaCl2 was superior to NaCl. This observation was ascribed to the reduction of net surface charge with increasing salt concentration as well as the promotion of protein-protein interactions at the air/water interface. Overall, certain transfer of salt type- and concentration-dependent effects from bulk solution to surface functionality was established, though no straight correlation between bulk, surface and foaming characteristics was detected.

Dilational surface elasticity of spread monolayers of pulmonary lipids in a broad range of surface pressure

A new approach to the analysis of nonlinear surface dilational rheological properties was developed with the aim to enlarge the accessible range of surface pressures. The dilational surface elasticity of spread monolayers of DPPC, cholesterol, DMEA and their mixtures was determined in the region of low surface tensions (less than 10 mN/m) corresponding to the state of pulmonary surfactants at the lung interface. The dilational surface elasticity of pure DPPC monolayer proved to be high (∼200 mN/m) up to the collapse. The addition of cholesterol, DMEA or their mixture to the DPPC monolayer increased the dynamic surface elasticity, but could decrease significantly the surface pressure of the monolayer collapse if the concentration of additions exceeds an optimal value.

Influence of the surface limiting elasticity modulus on the impact behavior of droplets of difenoconazole-loaded mesoporous silica nanoparticles with associated SDS.

The relation between the surface limiting elasticity modulus, ε0, of difenoconazole-loaded mesoporous silica nanoparticle (DF-MSN) formulations with associated SDS and the height of the first returning droplet impacting on cabbage and rice leaf surfaces was investigated. The surface dilational rheology properties were determined by means of surface tension relaxation. The impact of a droplet on the leaf surface was recorded with a high-speed camera. The surface limiting elasticity modulus, ε0, shows differences with different SDS concentrations. A positive correlation between droplet first rebound height and the surface limiting elasticity modulus, ε0, is observed. The pesticide droplet impact on the target leaf surface is a rather complex phenomenon, so the focus of this article is to establish a relationship between the surface limiting elasticity modulus, ε0, and droplet first rebound height. These findings introduce a chemical way to affect the impact behavior of pesticide droplets on target crop leaf surfaces, which may be of particular importance for pesticide spraying and crop protection, especially for hydrophobic and superhydrophobic target crops.

Surface dilational rheology of betaine surfactants: Effect of molecular structures

Measurements of the surface dilational rheological properties have been carried out for aqueous solutions of four zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine (C16PB), guerbet alcohol hexadecyl glycidyl ether glycine betaine (C16GPB), hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine (C16(EO)3PB) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether glycine betaine (C16G(EO)3PB), using the oscillating bubble method. The influences of surface ageing time, surface pressure, dilational frequency and bulk concentration on surface rheological properties have been expounded. It is found that the whole hydrophilic part of betaine molecule inclines to flat on the surface when betaine adsorbs, which will lead to higher dilational modulus. The nature of adsorption film is determined by in-surface processes, such as the variation of orientation of hydrophilic group. The branched hydrophobic alkyl chains of betaine molecules improve the intermolecular interactions, not only results in higher moduli, but causes a maximum in dynamic elastic modulus at high concentration. This indicates that the strength of surface film is strongly related to molecular arrangement, not simply determined by the surface molecule concentration. When ethylene oxide groups are incorporated in the hydrophobic group, the enhancement of steric hindrance will decrease both elastic modulus and viscous modulus.

Surface rheology and its relation to foam stability in solutions of sodium decyl sulfate

The anionic surfactant sodium decyl sulfate (SDeS) at concentrations below its critical micellar concentration (cmc) was studied in a surface chemically purified state at the air–water interface in terms of its static and dynamic interfacial properties. Equilibrium surface tension was determined using a pendant drop tensiometer. An oscillating bubble capillary pressure tensiometer allowed accessing the surface dilatational properties of the surfactant's adsorption layers in a frequency range from 2 to 500Hz. The estimation of single foam lamella stability was obtained from visual observation of films formed within a rectangular glass frame in a saturated atmosphere. Upon increasing surfactant concentration, the foam lamellae were found to rupture at prolonged lifetimes. The dramatic difference in foam stability goes along with a pronounced transition from a surface elastic to a surface visco-elastic state of the adsorption layers. These findings were indicative for a correlation between foam lamella stability and surface viscoelasticity also for this model surfactant. These results may be of importance to further shed light on the processes governing foam and foam lamella stability.

Interfacial Dynamic Properties and Dilational Rheology of Sulfonate Gemini Surfactant and its Mixtures with Quaternary Ammonium Bromides at the Air–Water Interface

AbstractThe dynamic interfacial properties and dilational rheology of gemini sulfonate surfactant (SGS) and its mixtures with quaternary ammonium bromides (DTAB, CTAB) at the air–water interface were investigated using drop shape analysis. Results suggest that the adsorption process of these surfactants is diffusion‐controlled at dilute concentrations, whereas the adsorption mechanism gradually shifts to a mixed kinetic‐diffusion control with increasing surfactant concentration. The mixed surfactant system possesses the best surface activity when the molar ratios of SGS/DTAB and SGS/CTAB mixtures are 9:10. The formation of catanionic complexes shields the electrostatic repulsion between surfactant molecules and lowers the electrostatic adsorption barrier. Therefore, SGS/DTAB and SGS/CTAB mixtures exhibit higher adsorption rates than either component alone. The effects of oscillating frequency and surfactant concentration on the surface dilational properties of SGS, DTAB, CTAB, SGS/DTAB, and SGS/CTAB mixtures were also determined. As the oscillating frequency increases, the dilational elasticity of these surfactants gradually increases. The dilational elasticity peaks at a certain concentration, which is less than the critical micelle concentration (CMC). Results show that the dilational elasticity of SGS/DTAB and SGS/CTAB mixtures is higher than that of either component, resulting from the formation of a denser monomolecular adsorption layer at the air–water interface. Our study provides a basis for understanding the interaction mechanism of catanionic surfactant mixtures containing Gemini surfactant at the air–water interface.

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.

Surface dilatational properties of Gemini surfactants containing multiple hydroxyl groups

Surfactant adsorption films at the air/water interface, which usually exert a significant influence over system behaviour, are closely related to the surfactant molecular structure. In this research, a series of Gemini surfactants containing four hydroxyl groups at the head groups, namely: alkanediyl-α,ω-bis[di(2-hydroxylethyl) dodecylammonium bromide], abbreviated to 12(2OH)-s-12(2OH), where s = 3, 6, 8 and 10, respectively, were investigated by using interfacial dilatational rheological measurements. The effects of oscillating frequency, bulk concentration and spacer length on the dilatational behaviour of 12(2OH)-s-12(2OH) were investigated. The variation of dilatational modulus of 12(2OH)-8-12(2OH) with concentrations showed two peaks which were attributed to different configurations adopted by the spacer, revealing the effects of dynamic configuration of the spacer on surfactant interfacial adsorption. The fit to the results, with that data available, using the Lucassen/van den Tempel (LVT) model showed that the presence of hydroxyl groups near the head groups of Gemini surfactants enhanced the interfacial elasticity of the adsorption films.

Multiscale approach to characterize bulk, surface and foaming behavior of casein micelles as a function of alkalinisation

Caseins display the major protein fraction in milk, and thus, significantly impact on milk's techno-functional properties such as foaming. As the micellar structure is mainly stabilized by hydrophobic as well as electrostatic forces, a gradual increase in pH value from 6.0 to 11.0 induced pronounced structural modifications. In consequence of alkalinisation, micelle size and composition changed. This had an impact on the solution properties such as turbidity. Furthermore, interfacial characteristics, e.g. surface pressure evolution and surface dilatational properties were affected. Different situations occurred regarding interfacial covering, which was also reflected in the resulting foam structures. The highest foam stability was obtained for pH 9.0. At this pH, highly voluminous casein micelles combined with a considerable amount of serum casein formed maximal viscoelastic surface layers. Micelle dissociation reduced viscoelasticity as well as foam stability, whilst drainage increased.