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[Display omitted] Two major protein families are present in rapeseed, namely cruciferins and napins. The structural differences between the two protein families indicate that they might behave differently when their mixture stabilises oil–water interfaces. Therefore, this work focuses on elucidating the role of both proteins in interface and emulsion stabilisation. Protein molecular properties were evaluated, using SEC, DSC, CD, and hydrophobicity analysis. The oil–water interface mechanical properties were studied using LAOS and LAOD. General stress decomposition (GSD) was used as a novel method to characterise the nonlinear response. Additionally, to evaluate the emulsifying properties of the rapeseed proteins, emulsions were prepared using pure napins or cruciferin and also their mixtures at 1:3, 1:1 and 3:1 (w:w) ratios. Cruciferins formed stiff viscoelastic solid-like interfacial layers (G s ′ = 0.046 mN/m; E d ′ = 30.1 mN/m), while napin formed weaker and more stretchable layers at the oil–water interface (G s ′ = 0.010 mN/m; E d ′ = 26.4 mN/m). As a result, cruciferin-formed oil droplets with much higher stability against coalescence (coalescence index, CI up to 10%) than napin-stabilised ones (CI up to 146%) during two months of storage. Both proteins have a different role in emulsions produced with napin-cruciferin mixtures, where cruciferin provides high coalescence stability, while napin induces flocculation. Our work showed the role of each rapeseed protein in liquid–liquid multiphase systems. [ABSTRACT FROM AUTHOR]

In recent years, there is a growing trend from both academia and the industry towards the use of “clean-labeled” ingredients obtained from renewable resources. Proteins and polysaccharides, in particular, are becoming increasingly popular as alternatives to already well-established synthetic surfactants. Quince seeds are a relatively novel hydrocolloid source that has recently raised interest among researchers due to their strong surface activity and viscosity-enhancing properties. This study investigates quince seed extract's surface properties (dynamic surface tension and dilatational surface rheology) and how they differ with varying concentrations (between 0.01% and 1%), pH's (3, 7, 9, and 11), and ionic strengths (0.1, 0.3, 0.5 M NaCl). By QSE addition alone, equilibrium surface tension could be lowered to ∼36 mN/m, which is lower than the lowest ST that can be achieved with many other surface active biopolymers. Critical aggregation concentration (CAC) was identified as 0.165% w/v, meaning a relatively low extract concentration was sufficient to provide complete surface coverage. Dynamic surface tension curves revealed almost instantaneous polymer adsorption for concentrations over 0.01% w/v, which demonstrates the strong potential of the gum as a foaming agent. As solution pHs get further from the isoelectric point of QSE proteins, the rate of adsorption of QSE molecules onto the interface and the equilibrium surface pressures increased. Surface properties were also significantly affected by the ionic strength of the medium, with eq. STs decreasing with increasing QSE concentration. pH and ionic strength induced conformational changes in the interfacial layer and also led to local minima and maxima in dilatational elastic and loss modulus within ranges studied. Considering these findings, QSE is a very promising natural alternative to other polymeric surfactants and stabilizers currently used in the food, cosmetic and pharmaceutical industries.

[Display omitted] • Weakly cohesive Chitosan microcapsules were deformed up to breakup in an extensional flow with orthogonal observations. • Two mechanisms of rupture regimes of microcapsules were revealed: fluid-like and solid-like behaviours. • The dual response of microcapsule rupture in flow is closely correlated to the shell structure. The controlled rupture of a core–shell capsule and the timely release of encapsulated materials are essential steps of the efficient design of such carriers. The mechanical and physico-chemical properties of their shells (or membranes) mainly govern the evolution of such systems under stress and notably the link between the dynamics of rupture and the mechanical properties. This issue is addressed considering weakly cohesive shells made by the interfacial complexation of Chitosan and PFacid in a planar extensional flow. Three regimes are observed, thanks to the two observational planes. Whatever the time of reaction in membrane assembly, there is no rupture in deformation as long as the hydrodynamic stress is below a critical value. At low times of complexation (weak shear elastic modulus), the rupture is reminiscent of the breakup of droplets: a dumbell or a waist. Fluorescent labelling of the membrane shows that this process is governed by continuous thinning of the membrane up to the destabilization. It is likely that the membrane shows a transition from a solid to liquid state. At longer times of complexation, the rupture has a feature of solid-like breakup (breakage) with a discontinuity of the membrane. The maximal internal constraint determined numerically marks the initial location of breakup as shown. The pattern becomes more complex as the elongation rate increases with several points of rupture. A phase diagram in the space parameters of the shear elastic modulus and the hydrodynamic stress is established. [ABSTRACT FROM AUTHOR]

[Display omitted] Silicone oil (SO) migration into the drug product of combination products for biopharmaceuticals during storage is a common challenge. As the inner barrel surface is depleted of SO the extrusion forces can increase compromising the container functionality. In this context we investigated the impact of different formulations on the increase in gliding forces in a spray-on siliconized pre-filled syringe upon storage at 2–8 °C, 25 °C and 40 °C for up to 6 months. We tested the formulation factors such as surfactant type, pH, and ionic strength in the presence of one monoclonal antibody (mAb) as well as compared three mAbs in one formulation. After 1 month at 40 °C, the extrusion forces were significantly increased due to SO detachment dependent on the fill medium. The storage at 40 °C enhanced the SO migration process but it could also be observed at lower storage temperatures. Regarding the formulation factors the tendency for SO migration was predominantly dependent on the presence and type of surfactant. Interestingly, when varying the mAb molecules, one of the proteins showed a rather stabilizing effect on the SO layer resulting into higher container stability. In contrast to the formulation factors, those different stability outcomes could not be explained by interfacial tension (IFT) measurements at the SO interface. Further characterization of the mAb molecules regarding interfacial rheology and conformational stability were not adequately able to explain the observed difference. Solely a hydrophobicity ranking of the molecules correlated to the stability outcome. Further investigations are needed to clarify the role of the protein in the SO detachment process and to understand the cause for the stabilization. However, the study clearly demonstrated that the protein itself plays a critical role in the SO detachment process and underlined the importance to include verum for container stability. [ABSTRACT FROM AUTHOR]

The application of surface rheology and Brewster angle microscopy on mixed monolayers of DPPC and polymeric nanoparticles (cationic and anionic) showed that the sign of the particle charge affects the dynamic properties of the monolayers less than the nanoparticles' ability to aggregate. Under almost physiological conditions, the effect of nanoparticles on the elasticity of DPPC monolayer is insignificant. However, the particles prevent the surface tension from decreasing to extremely low values. This effect could affect the functionality of pulmonary surfactants. [ABSTRACT FROM AUTHOR]

[Display omitted] Hypothesis: Plant seeds store lipids in oleosomes, which are storage organelles with a triacylglycerol (TAG) core surrounded by a phospholipid monolayer and proteins. Due to their membrane components, oleosomes have an affinity for the air/oil–water interface. Therefore, it is expected that oleosomes can stabilise interfaces, and also compete with proteins for the air–water interface. Experiments: We mixed rapeseed oleosomes with whey protein isolate (WPI), and evaluated their air–water interfacial properties by interfacial rheology and microstructure imaging. To understand the contribution of the oleosome components to the interfacial properties, oleosome membrane components (phospholipids and membrane proteins) or rapeseed lecithin (phospholipids) were also mixed with WPI. Findings : Oleosomes were found to disrupt after adsorption, and formed TAG/phospholipid-rich regions with membrane fragments at the interface, forming a weak and mobile interfacial layer. Mixing oleosomes with WPI resulted in an interface with TAG/phospholipid-rich regions surrounded by whey protein clusters. Membrane components or lecithin mixed with proteins also resulted in an interface where WPI molecules aggregated into small WPI domains, surrounded by a continuous phase of membrane components or phospholipids. We also observed an increase in stiffness of the interfacial layer, due to the presence of oleosome membrane proteins at the interface. [ABSTRACT FROM AUTHOR]

Physicochemical properties of lipid monolayer depend on its composition where a blend of lipids exhibit superior behaviour than the individual component. Surface pressure (π) – area (A) isotherms of mixed monolayer (PCmix) formed by dipalmitoylphosphatidylcholine (DPPC), palmitoleylphosphatidylcholine (POPC), soyphosphatidylcholine (SPC) and hydrogenated soy phosphatidylcholine (HSPC) in combination with 30 mole % cholesterol (Chol) were obtained by using Langmuir trough. Effects of dipalmitoylphosphatidyethanolamine (DPPE) on its mutual miscibility at the air-water interface with DPPC ​+ ​Chol, POPC ​+ ​Chol, HSPC ​+ ​Chol and SPC ​+ ​Chol were also investigated separately, followed by studying the effects of DPPE and dipalmitoylphosphatidylglycerol (DPPG) to PCmix ​+ ​Chol and PCmix ​+ ​DPPE ​+ ​Chol respectively. Lift-off area, minimum molecular area, excess molecular area, collapse pressure, Gibbs free energy of interfacial mixing, compressibility modulii values were evaluated by analyzing the isotherms. Deviations from the ideal mixing behaviours were dependent on the composition of the lipid blends. Surface dilatational rheology studies could assess monolayer elasticity, whereas the film morphologies were analysed by Brewster angle microscopic (BAM) studies. DPPC induced formation of condensed monolayer, whereas film rigidity was increased with the incorporation of DPPE and DPPG into mixed systems. Interactions among the lipid components of the investigated mixed systems were thoroughly discussed from the point of view of polar head and acyl chain saturation and obtained results follow the sequence: PCmix ​+ ​DPPE ​+ ​DPPG ​+ ​Chol ​> ​PCmix ​+ ​DPPE ​+ ​Chol ​> ​individual PC ​+ ​DPPE ​+ ​Chol which could be translated into the bilayer studies. Such investigation of mixed lipid is important for class of its own composition and combined results are expected to contribute in better understanding the interaction of selected lipid in proposed blend.

The application of surface rheology and Brewster angle microscopy on mixed monolayers of DPPC and polymeric nanoparticles (cationic and anionic) showed that the sign of the particle charge affects the dynamic properties of the monolayers less than the nanoparticles’ ability to aggregate. Under almost physiological conditions, the effect of nanoparticles on the elasticity of DPPC monolayer is insignificant. However, the particles prevent the surface tension from decreasing to extremely low values. This effect could affect the functionality of pulmonary surfactants.

At low mole fractions, cholesterol segregates into 10- to 100-nm-diameter nanodomains dispersed throughout primarily dipalmitoylphosphatidylcholine (DPPC) domains in mixed DPPC:cholesterol monolayers. The nanodomains consist of 6:1 DPPC:cholesterol complexes that decorate and lengthen DPPC domain boundaries, consistent with a reduced line tension, λ. The surface viscosity of the monolayer, ηs, decreases exponentially with the area fraction of the nanodomains at fixed surface pressure over the 0.1- to 10-Hz range of frequencies common to respiration. At fixed cholesterol fraction, the surface viscosity increases exponentially with surface pressure in similar ways for all cholesterol fractions. This increase can be explained with a free-area model that relates ηs to the pure DPPC monolayer compressibility and collapse pressure. The elastic modulus, G, initially decreases with cholesterol fraction, consistent with the decrease in λ expected from the line-active nanodomains, in analogy to 3D emulsions. However, increasing cholesterol further causes a sharp increase in G between 4 and 5 mol% cholesterol owing to an evolution in the domain morphology, so that the monolayer is elastic rather than viscous over 0.1-10 Hz. Understanding the effects of small mole fractions of cholesterol should help resolve the controversial role cholesterol plays in human lung surfactants and may give clues as to how cholesterol influences raft formation in cell membranes.

Saponins are natural surfactants which can provide highly viscoelastic interfaces. This property can be used to quantify precisely the effect of interfacial dilatational elasticity on the various rheological properties of bulk emulsions. We measured the interfacial dilatational elasticity of adsorption layers from four saponins (Quillaja, Escin, Berry, Tea) adsorbed on hexadecane-water and sunflower oil-water interfaces. In parallel, the rheological properties under steady and oscillatory shear deformations were measured for bulk emulsions, stabilized by the same saponins (oil volume fraction between 75 and 85%). Quillaja saponin and Berry saponin formed solid adsorption layers (shells) on the SFO-water interface. As a consequence, the respective emulsions contained non-spherical drops. For the other systems, the interfacial elasticities varied between 2 mN/m and 500 mN/m. We found that this interfacial elasticity has very significant impact on the emulsion shear elasticity, moderate effect on the dynamic yield stress, and no effect on the viscous stress of the respective steadily sheared emulsions. The last conclusion is not trivial, because the dilatational surface viscoelasticity is known to have strong impact on the viscous stress of steadily sheared foams. Mechanistic explanations of all observed effects are described. [ABSTRACT FROM AUTHOR]

The hypothesis was that saccharides mediate interactions between surface-active components and that this will have an impact on foam decay during the drying process. Static light scattering was performed to determine changes in interactions between the foam stabilizer on a molecular level. Furthermore, pendant drop and oscillating drop measurements were performed to examine the surface tension and surface rheology. Foams were dried in conventional dryers as well as microwave-supported vacuum dryers. Final foam properties were determined. It was shown that the addition of sugars, often added as protective substances for sensitive organic molecules, resulted in lower repulsion between different types of surface-active components, namely polysorbate 80 and β-lactoglobulin (β-lg). Differences in impact of the types of sugars and between different types of surfactant, protein, and small molecules were observed influencing the foam decay behavior. The interfacial properties of polysorbate 80 and β-lg were influenced by the type of the used sugars. The surface elasticity of protein stabilized surfaces was higher compared to that of polysorbate stabilized systems. Protein stabilized systems remained more stable compared to polysorbate systems, which was also affected by the used saccharide. Overall, a correlation between molecular interactions and foam decay behavior was found.

Purpose: To provide new insights into how protein-surfactant competitive adsorbtion and corresponding surface tension reduction properties at the air-water and oil-water interface are impacted by the type of protein and the associated protein surface rheology. Method: Interfacial Rheology was utilized to obtain surface G' and G" as a function of frequency. Force tensiometry was utilized to obtain changes in surface tension as a function of surfactant concentration. The impact on surface properties of two different proteins i.e. BSA and Lysozyme was investigated as a function of surfactant concentration i.e. polysorbates PS 20, PS 80 and Poloxomer (Kolliphor P188). Results: Surface tension and interfacial tension measurements for BSA showed that in mixed BSA/polysorbate surfactant systems, BSA dominates the interfacial behavior at both the air-water and oil-water interfaces, until a high polysorbate concentration of 0.1 mg/ml. At these high polysorbate concentrations a mixed BSA-Polysorbate interfacial layer is formed as corroborated by the surface elasticity values being lower than that of pure BSA but higher than that of pure Polysorbate. For Kolliphor, it was observed that Kolliphor was unable to displace BSA at any concentration. This is corroborated by the high surface elasticity of the BSA which is maintained in the presence of Kolliphor. Surface and interfacial tension measurements for lysozyme show that for mixed lysozyme/polysorbate surfactant systems, the surface tension values are lower than that exhibited by either the lysozyme or the polysorbate surfactants. This potentially indicates the formation of a mixed layer of lysozyme and polysorbate. At the high polysorbate concentrations probed, the surface elasticity values are however closer to that of pure polysorbates, indicating that the mixed layer may be more heavily polysorbate dominated, especially at high polysorbate concentrations. For Kolliphor, the response was similar to that seen in the Kolliphor-BSA system in which the Kolliphor was not able to displace the protein i.e. Lysozyme. Conclusions: In conclusion, it was seen that competitive adsorption between proteins and common excipient surfactants is dictated by the type of protein and its effective structuring/rigidity at the surface as reflected through surface elasticity and surface tan delta values. BSA was seen to exhibit a higher surface elasticity than lysozyme, and therefore has a more rigid structure and is more competitive at the interface. [ABSTRACT FROM AUTHOR]

Direct physicochemical interactions between the major components of electronic cigarette liquids (e-liquids): glycerol (VG) and propylene glycol (PG), and lung surfactant (LS) were studied by determining the dynamic surface tension under a simulated breathing cycle using drop shape method. The studies were performed for a wide range of concentrations based on estimated doses of e-liquid aerosols (up to 2500 × the expected nominal concentrations) and for various VG/PG ratios. The results are discussed as relationships among mean surface tension, surface tension amplitude, and surface rheological properties (dilatational elasticity and viscosity) versus concentration and composition of e-liquid. The results showed that high local concentrations (>200 × higher than the estimated average dose after a single puffing session) may induce measurable changes in biophysical activity of LS; however, only ultra-high e-liquid concentrations inactivated the surfactant. Physiochemical characterization of e-liquids provide additional insights for the safety assessment of electronic nicotine delivery systems (ENDS). [ABSTRACT FROM AUTHOR]

Hypothesis Previous efforts to formulate smart foams composed of mixtures of PNIPAAm, a thermoresponsive uncharged polymer, and surfactants have failed because the surfactant displaces the PNIPAAm from the liquid-air interface, removing the thermal responsiveness. We hypothesized that thermoresponsive foams could be formulated with such a mixture if a charged surfactant were used in order to anchor an oppositely charged brush-type polyelectrolyte, for which PNIPAAm could be incorporated as side chains, to the interface. Experiments A brush-type negatively charged co-polyelectrolyte (Cop-L) with PNIPAAm as side chains was synthetized. Its mixtures with DTAB, a cationic surfactant, in aqueous solution were characterized by dynamic light scattering, surface tension and surface compression viscoelasticity measurements, as a function of both surfactant concentration and temperature. The foam stability and its responsiveness to temperature changes were studied with a homemade apparatus. Findings The Cop-L/DTAB mixtures were capable of producing thermoresponsive foams but only in a very narrow surfactant concentration (c s ) range, 0.3 < c s < 1.6 mM. The responsiveness is due to a modification of the interfacial compression elasticity induced by conformational changes of the Polyeletrolyte/surfactant aggregates at the interface. This is possible only for c s  < 1.6 because higher surfactant concentrations induce the polymer collapse at all temperatures, eliminating the thermal responsiveness. [ABSTRACT FROM AUTHOR]

Bubble Ostwald ripening (OR) leads to a gradual increase of the mean bubble size in foams with time. The rate of OR can be reduced significantly or even arrested completely using appropriate solid particles and/or surfactants as foam stabilizers. In the current paper, we show that saponins, a widespread class of natural surfactants, can reduce significantly the rate of OR in foams. To reveal the reasons for the reduced rate of OR in saponin-stabilized foams, we performed measurements of the rate of bubble diminishing, for single air bubbles placed below a solution surface, with a series of saponin bio-surfactants. These saponin surfactants form adsorption layers with surface elasticity, spanning a very wide range – from almost zero up to several thousand mN/m. The measured rate of bubble OR showed no correlation with the surface elastic modulus (dilatational or shear), as measured at 0.1 Hz frequency of surface oscillations. A reasonable correlation was observed only with the surface stress (deviation from the equilibrium surface tension), measured at very slow rate of surface deformation, which mimics much better the actual processes of bubble OR in foams – higher surface stress corresponds to lower OR rate. New theoretical expression, accounting for the out-of- equilibrium surface tension during bubble shrinkage and for the gas flux across the meniscus regions surrounding the foam films, was derived and used to calculate theoretically the rate of bubble diminishing. The comparison of the theoretical predictions with the experimental data shows clearly that the main reason for the reduced rate of OR in the studied systems is the high resistance to gas transfer of the saponin adsorption layers. The deviations from the equilibrium surface tension, although noticeable, have smaller effect. The complementary experiments with actual foams showed that the rate of OR is even lower (compared to the rate measured with single bubbles) which is explained with the thicker non-equilibrium foam films, formed between the neighboring bubbles in saponin-stabilized foams. [ABSTRACT FROM AUTHOR]

From the recent advent of the new soft-micro technologies, the hydrodynamic theory of surface modes propagating on viscoelastic bodies has reinvigorated this field of technology with interesting predictions and new possible applications, so recovering its scientific interest very limited at birth to the academic scope. Today, a myriad of soft small objects, deformable meso- and micro-structures, and macroscopically viscoelastic bodies fabricated from colloids and polymers are already available in the materials catalogue. Thus, one can envisage a constellation of new soft objects fabricated by-design with a functional dynamics based on the mechanical interplay of the viscoelastic material with the medium through their interfaces. In this review, we recapitulate the field from its birth and theoretical foundation in the latest 1980s up today, through its flourishing in the 90s from the prediction of extraordinary Rayleigh modes in coexistence with ordinary capillary waves on the surface of viscoelastic fluids, a fact first confirmed in experiments by Dominique Langevin and me with soft gels [Monroy and Langevin, Phys. Rev. Lett. 81, 3167 (1998)]. With this observational discovery at sight, we not only settled the theory previously formulated a few years before, but mainly opened a new field of applications with soft materials where the mechanical interplay between surface and bulk motions matters. Also, new unpublished results from surface wave experiments performed with soft colloids are reported in this contribution, in which the analytic methods of wave surfing synthetized together with the concept of coexisting capillary-shear modes are claimed as an integrated tool to insightfully scrutinize the bulk rheology of soft solids and viscoelastic fluids. This dedicatory to the figure of Dominique Langevin includes an appraisal of the relevant theoretical aspects of the surface hydrodynamics of viscoelastic fluids, and the coverage of the most important experimental results obtained during the three decades of research on this field. [ABSTRACT FROM AUTHOR]

The dynamic surface properties of mixed monolayers of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and negatively charged polystyrene particles (PS) of different size were investigated with the aim to model the interactions of particles with biointerfaces. Special attention was paid to the aggregation of the particles at the water/air interface. The particle aggregates have a weaker influence on the dynamic properties of DPPC monolayers as compared with non-aggregated particles because of a shorter three phase contact line. The incorporation of particles into a DPPC monolayer leads to disordering of the monolayer structure, decreases the changes of surface properties in the course of two-dimensional phase transitions and the dynamic surface elasticity of the condensed lipid film. The influence of particles on the properties of mixed monolayers depends strongly on the ratio of lipid molecules and particles, and decreases with the decrease of particle surface concentration. The Brewster angle microscopy gives direct evidence of the PS particle aggregation in the course of compression of mixed monolayers. [ABSTRACT FROM AUTHOR]

The dewetting behavior of surfactant solutions differs from pure liquids due to the possibility of generating Marangoni stresses near the receding contact line. Specifically, for surfactant solutions the dynamic receding contact angle decreases much stronger with increasing dewetting speed than of pure liquids with similar viscosity and surface tension. To gain a better understanding of the correlation between the dynamics of dewetting and the properties of the surfactants (e.g. surface activity, micelle formation, surface rheology) we compare high molecular weight surfactants to low molecular weight surfactants. We investigate the forced wetting of aqueous solutions of Pluronic F-127 (a {poly-ethylene-oxide}-{poly-propylene-oxide}-{poly-ethylene-oxide} triblock copolymer), with a molecular weight of M w = 12 kg/mol, roughly 50 times larger than an average size surfactant, like cetyltrimethylammonium bromid (CTAB). Pluronic F-127 is more surface active than CTAB and already a nanomolar concentration affects the surface tension. Similar to smaller surfactants Pluronic F-127 decreases the dynamic receding contact angle. However, the change in the dynamic receding contact angle is more pronounced. In case of Pluronic F-127 already concentrations below 0.1 %CMC (critical micelle concentration) led to a substantial decrease in dynamic receding contact angle. With a combination of dewetting experiments, surfaces rheology and bulk measurements of aggregate concentrations, we show that the concentration of full surface coverage (CFSC) is the relevant concentration scale. Only in the case of low molecular weight surfactant this concentration is close to the critical micelle concentration (CMC). In the case of Pluronic F-127 the CFSC and the CMC differ by about three orders of magnitude. [ABSTRACT FROM AUTHOR]

The two main continuum frameworks used for modeling the dynamics of soft multiphase systems are the Gibbs dividing surface model, and the diffuse interface model. In the former the interface is modeled as a two dimensional surface, and excess properties such as a surface density, or surface energy are associated with this sharp interface. Its motion and deformation, and the time evolution of the excess fields associated with it are calculated by a set of partial differential equations (the jump balances), which have to be solved together with the mass, momentum, and energy balances of the bulk phases. A wide range of phenomena have been modeled in this framework, such as the deformation of emulsion droplets in a flow field, the effects of interfacial rheology on multiphase flows, wave phenomena in stratified flows, bubbles rising in a quiescent liquid, phase separation in immiscible mixtures, wetting phenomena, and in-plane and cross-plane mass and heat transfer. In the diffuse interface model the interface is modeled as a three dimensional region of finite thickness, in which order parameters change continuously from their value in one bulk phase to their value in the adjoining bulk phase. The model starts from a free energy functional which contains nonlocal contributions, which to leading order are represented by a square gradient term of the order parameter. The spatial distribution of density or concentration within the interfacial region is then determined by free energy minimization. When a simple pairwise inter-particle potential is assumed, a natural extension of the van der Waals model of phase transitions is obtained. Assuming a simple constitutive relation for the diffusive material fluxes in very viscous binary mixtures, the Cahn–Hilliard theory of spinodal decomposition can be obtained. For systems where convective material fluxes cannot be neglected, a reversible body force, called Korteweg force, must be added to the Navier–Stokes equation, which is proportional to the chemical potential gradient. This force is non-zero only for systems not at equilibrium, and is responsible for the strong convection observed in phase separating mixtures, while it is absent in systems where chemical potentials are uniform. Like the Gibbs dividing surface model, the diffuse interface model has been applied to a wide range of phenomena, such as mixing and demixing in binary mixtures, buoyancy driven detachment of wall-bound droplets, droplet breakup and coalescence, Marangoni effects, and flow in nano- and microchannels. Here we discuss the derivation of the governing equations of these two frameworks, and compare their strengths and weaknesses. We also show how these two frameworks can be combined to solve multiphase problems more effectively. [ABSTRACT FROM AUTHOR]

Foam stability of casein micelle dispersions (CMDs) strongly depends on aggregate size. To elucidate the underlying mechanism, the role of interfacial and thin film properties was investigated. CMDs were prepared at 4 °C and 20 °C, designated as CMD 4 °C and CMD 20 °C . At equal protein concentrations, foam stability of CMD 4 °C (with casein micelle aggregates) was markedly higher than CMD 20 °C (without aggregates). Although the elastic modulus of CMD 4 °C was twice as that of CMD 20 °C at 0.005 Hz, the protein adsorbed amount was slightly higher for CMD 20 °C than for CMD 4 °C , which indicated a slight difference in interfacial composition of the air/water interface. Non-linear surface dilatational rheology showed minor differences between mechanical properties of air/water interfaces stabilized by two CMDs. These differences in interfacial properties could not explain the large difference in foam stability between two CMDs. Thin film analysis showed that films made with CMD 20 °C drained to a more homogeneous film compared to films stabilized by CMD 4 °C . Large casein micelle aggregates trapped in the thin film of CMD 4 °C made the film more heterogeneous. The rupture time of thin films was significantly longer for CMD 4 °C (>1 h) than for CMD 20 °C (<600 s) at equal protein concentration. After homogenization, which broke down the aggregates, the thin films of CMD 4 °C became much more homogeneous, and both the rupture time of thin films and foam stability decreased significantly. In conclusion, the increased stability of foam prepared with CMD 4 °C appears to be the result of entrapment of casein micelle aggregates in the liquid films of the foam. [ABSTRACT FROM AUTHOR]

A surface characterization of two types of unmodified chitosan properties with different molecular weight (MW) and deacetylation degree (DD) was carried out in terms of polymer concentration (a concentration lower than the saturation, the saturation concentration and a supersaturated concentration). The modification of the production conditions allowed to obtain chitosan samples with different properties (MW and DD), which eventually determined its surface activity. Thus, a kind of tailor-made chitosan may be designed to be adapted to different applications. Surface activity has been analysed by mean of measurements of surface tension, dilatational and shear rheology. The results have demonstrated that chitosan possessed a good surface activity at high ionic strength. Also, the increase in the concentration of chitosan in the solution, and the increase in molecular weight (and, therefore, a decrease in the degree of deacetylation) favoured the formation of aggregates, which improved the adsorption kinetics. The latter allowed adequate elasticity values to be reached more quickly. These properties are reached faster for the higher molecular weight chitosan (lower degree of deacetylation), due to the more hydrophobic character that facilitates the interactions between the adsorbed aggregates. Surface rheology revealed a predominantly elastic behaviour of chitosan film. All of these results strengthen the idea that chitosan behaves as a surface-active hydrophilic Pickering agent. [Display omitted] • Chitosan could be tailor-made for specific molecular weight and degree of deacetylation. • Chitosan from crab biowaste shows surface activity at high ionic strength. • Molecular weight and degree of deacetylation of chitosan determine surface properties. • Chitosan film shows a predominantly elastic behaviour. • Chitosan with a higher hydrophobic character has a greater tendency to aggregate. [ABSTRACT FROM AUTHOR]

• Sakuranetin formed a monomolecular film with DPPE at the air-water interface. • Physicochemical properties were evaluated. • The drug interact with the lipid monolayer at the lipid-air interface. Sakuranetin, a natural flavonoid isolated as the main compound from roots of the Brazilian plant Baccharis retusa (Asteraceae), was incorporated in lipid membranes as Langmuir monolayers. For that, the mammalian lipid dipalmitoyl phosphatidylethanolamine (DPPE) was chosen. Sakuranetin condensed the monolayers at high surface pressures, decreased the surface compression modulus and reduced the molecular order of the acyl chains (reduction of all- trans/gauche conformers ratio), and increased the heterogeneity of the interface, forming aggregates. These combined results lead to the conclusion that this lipophilic compound may interact with the lipidic layers, preferentially at the lipid-air interface, to minimize the free energy, and reaches such conformation disturbing the thermodynamic, structural, mechanical, rheological, and morphological properties of the well-packed DPPE monolayer. [ABSTRACT FROM AUTHOR]