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The input of chemical and physical sciences to life sciences is increasingly important. Surface science as a complex multidisciplinary research area provides many relevant practical tools to support research in medicine. The tensiometry and surface rheology of human biological liquids as diagnostic tools have been very successfully applied. Additionally, for the characterization of pulmonary surfactants, this methodology is essential to deepen the insights into the functionality of the lungs and for the most efficient administration of certain drugs. Problems in ophthalmology can be addressed using surface science methods, such as the stability of the wetting films and the development of artificial tears. The serious problem of obesity is fast-developing in many industrial countries and must be better understood, while therapies for its treatment must also be developed. Finally, the application of fullerenes as a suitable system for detecting cancer in humans is discussed. [ABSTRACT FROM AUTHOR]

Profile analysis tensiometry (PAT) with drops and bubbles is a successful methodology to characterize liquid–fluid interfaces. Questions about the most suitable size of drops and bubbles have been solved now on the basis of dimensionless numbers. The consideration of the standard deviation between measured and calculated liquid profiles as a sensitive measure for the applicability of PAT provides a tool for its correct use. For solutions of highly surface-active compounds, bulk depletion effects can cause systematic errors in the analysis of adsorption kinetics, equations of state, and the visco-elastic interfacial behavior of liquid adsorption layers. Great progress has been made in measurements of interfacial dilational rheology with large amplitude perturbations providing additional information about structure and dynamics of complex adsorption layers. Also, first attempts are successfully made to use artificial intelligence (AI) to enhance the efficiency of PAT applications. Thus, PAT has established a solid position in surface science. [Display omitted] [ABSTRACT FROM AUTHOR]

The input of chemical and physical sciences to life sciences is increasingly important. Surface science as a complex multidisciplinary research area provides many relevant practical tools to support research in medicine. The tensiometry and surface rheology of human biological liquids as diagnostic tools have been very successfully applied. Additionally, for the characterization of pulmonary surfactants, this methodology is essential to deepen the insights into the functionality of the lungs and for the most efficient administration of certain drugs. Problems in ophthalmology can be addressed using surface science methods, such as the stability of the wetting films and the development of artificial tears. The serious problem of obesity is fast-developing in many industrial countries and must be better understood, while therapies for its treatment must also be developed. Finally, the application of fullerenes as a suitable system for detecting cancer in humans is discussed.

Graphical abstract Abstract The dilational visco-elasticity of surfactant adsorption layers was measured at low frequencies by the drop profile analysis tensiometry using oscillating drops. As the studied non-ionic surfactant C 13 DMPO (tridecyl dimethyl phosphine oxide) is soluble in water and in hexane, the partitioning of the surfactant between the two solvents had to be taken into consideration. The diffusion controlled exchange of matter theory was generalized in order to take into consideration the curvature of the interface, the diffusional transport in both adjacent bulk phases as well as the transfer across the liquid interface. Using two configurations, i.e. water drop in hexane and hexane drop in water, it is shown that the frequency dependence of the visco-elasticity modulus and the phase angle can be well described when the correct partition coefficient is applied. The surface activity of the selected surfactant C 13 DMPO is optimum to demonstrate the impact of matter transfer across the interface on the dilational visco-elasticity of interfacial adsorption layers of non-ionic surfactants. [ABSTRACT FROM AUTHOR]

In mixed solutions of anionic and cationic surfactants, called catanionics, ion pairs are formed which behave like non-ionic surfactants with a much higher surface activity than the single components. In equimolar mixtures of NaCnSO4 and CmTAB, all surface-active ions are paired. For mixtures with n + m = const, the interfacial properties are rather similar. Catanionics containing one long-chain surfactant and one surfactant with medium chain length exhibit a strong increase in surface activity as compared with the single compounds. In contrast, catanionics of one medium- and one short chain surfactant have a surface activity similar to that of the medium-chain surfactant alone. Both the Frumkin model and the reorientation model describe the experimental equilibrium data equally well, while the adsorption kinetics of the mixed medium- and short-chain surfactants can be well described only with the reorientation model.

Surface tension experiments were performed using the drop profile analysis tensiometry method. The hexane was injected into the measuring cell at certain times before the formation of the solution drop. The influence of the capillary diameter and solution drop size on the measured apparent dynamic surface tension was studied. The amount of hexane transferred from the vapor phase to the drop was estimated. For large pure water drops, it was shown that the ageing of the drop in the hexane vapor during a long time resulted in the formation of a liquid hexane phase covering the drop, but the volume of this phase did not exceed 0.5 mm3. On the contrary, for surfactant solution drops the volume of the hexane phase covering the drop was essentially larger. Experiments with solution drops were performed to measure the surface tension within a wide range of surfactant concentration. It was found that the dependencies of dynamic surface tension on the C13DMPO and C14EO8 solutions concentration exhibit maxima at concentrations of about 1–2 μmol/L for C14EO8 and 2–5 μmol/L for C13DMPO at ageing times of 100 to 1000 s; these maxima were shown to exist also at equilibrium. This phenomenon is presumably ascribed to the competitive character of simultaneous adsorption of hexane and surfactant.

The surface tension of C13DMPO aqueous solution drops in hexane vapor is studied using the drop profile method. The hexane was injected into the measuring cell at three different conditions: before the formation of the solution drop, at a certain moment during the adsorption process, and after reaching the equilibrium of surfactant adsorption. The surface tension values for all experiments at the same concentration and different injection situations ultimately coincide with each other after attaining the final equilibration stage. The equilibrium surface tension isotherms of C13DMPO solutions, and the adsorption of both components—surfactant and hexane—were calculated. It was shown that the presence of surfactant leads to an increased hexane adsorption.

Dynamic surface tensions and dilational visco-elasticity are easy accessible parameters of liquids. For human body liquids, such as urine, blood serum, amniotic fluid, gastric juice, saliva and others, these parameters are very characteristic for the health status of people. In case of a disease the composition of certain liquids specifically changes and the measured characteristics of dynamic surface tension of the dilational surface elasticity and viscosity reflect these changes in a clear way. Thus, this kind of physico-chemical measurements represent sensitive tools for evaluating the severity of a disease and can serve as control tool for the efficiency of applied therapies. The overview summarises the results of a successful work over about 25 years on this subject and gives specific insight into a number of diseases for which the diagnostics as well as the therapy control have been significantly improved by the application of physico-chemical experimental techniques. [ABSTRACT FROM AUTHOR]

The dependence of the dynamic surface tension of water at the interface with saturated hexane and cyclohexane vapours was measured by the drop profile analysis method. The surface tension for the adsorption layers of cyclohexane at different temperatures was compared with the results reported earlier for the adsorption of hexane and other alkanes from the vapour phase on water drops. It is shown that cyclohexane is adsorbed significantly slower than the adsorption of hexane occurs, and is characterised by a much larger induction time. The error in the drop radius measurements at 40℃ attains 45 μm. The experimental rheologic characteristics of the adsorbed layers are studied and the results are compared with the model developed to describe an adsorption process governed by a kinetic mechanism. [ABSTRACT FROM AUTHOR]

On the basis of surface tension and surface visco-elasticity measurements performed using profile analysis tensiometry with single pendent drops the surface properties of the alkyl phospholipid Inositol-C2-PAF were determined. Because of the very low bulk concentrations of Inositol-C2-PAF used in the studies, the obtained adsorption data had to be analysed including the depletion of the bulk concentration due to adsorption at the surface of the measured drops. The determined critical micellar concentration (CMC) of aqueous Inositol-C2-PAF solutions was found to be 1.1 μM, similar to other anti-tumour and anti-inflammatory substances. [ABSTRACT FROM AUTHOR]

The influence of temperature on the dynamic surface tension of water in heptane vapour is studied using drop profile analysis tensiometry. The water drops are formed in air saturated by heptane and water vapours. For long life times a new phenomenon is found: a sharp decrease of surface tension from about 60 mN/m down to 30 mN/m. The time until this sharp surface tension sets in decreases with increasing temperature. This phenomenon is attributed to the formation of heptane adsorption layers with a significant thickness. To ensure that the sharp surface tension decrease is not an artefact, the experimental error (deviation of drop profiles from the Young-Gauss-Laplace equation) was determined using harmonic oscillations imposed to the surface of pure heptane drops. It was shown that fitting errors below 10 μm in the determination of the drop radius do not affect the calculated surface tension value. The sharp surface tension decrease was observed with fitting errors below 5 μm, so that this phenomenon was explained to be caused by the formation of multilayers. The surface tensions and adsorbed amounts are described by a model developed earlier. The experimental results depend essentially on the experimental method used. In another experiment the atmosphere in the measuring cell was pre-saturated only by water vapour, and heptane (pentane) was added onto the cell bottom just immediately before the water drop was formed. The increase of temperature results in a slower adsorption process which is opposite to the case where the composition of the mixed atmosphere inside the cell was established prior to the experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface activity of dyes is a key parameter for photocatalytic wastewater treatment. • Dynamic surface tension of Malachit Green (MG) and Eriochrom Black-T (EBT) show strong dependency to pH. • Novel characterization method is introduced for interactions of the catalyst nanoparticle with dye molecules based on dynamic surface properties analysis. • Photocatalytic wastewater treatment can be improved considering pollutants-catalyst interactions via dynamic surface tension and interfacial elasticity analysis. In photocatalytic processes for wastewater treatment, the degradation reactions mainly occurs at the surface of the catalyst and nearby regions. Therefore, understanding of the interactions between the catalyst and pollutant in a photocatalytic degradation system is of utmost importance, determining the affinity of the pollutant molecules to be attracted or repulsed from the photocatalyst particles. The aim of this experimental study is to get a better insight about the interactions between the catalyst nanoparticles and pollutant molecules via a novel characterization method based on dynamic surface phenomena analysis. Drop profile analysis tensiometry (PAT) is used for this purpose for dynamic surface tension and elasticity measurements of dye solutions (as pollutants), and in mixed solutions with catalyst particles at different pH conditions. The results demonstrate that the cationic dye Malachit Green (MG) has a low surface activity at pH 6.5, with an equilibrium surface tension about 69 mN/m. While it becomes much more surface active at pH 9 and surface tension is decreased to 59 mN/m. Adding TiO 2 nanoparticles to MG solution at pH 9 causes a significant increase in surface tension, with much slower dynamics of adsorption at air/water interface. These results indicate a significant attraction and attachment of MG molecules to the surface of TiO 2 nanoparticles, creating MG-TiO 2 complexes, which have mobility much slower than the free MG molecules. This observation is in a good correlation with observed higher efficiency of MG degradation around pH 9. The capability of this novel experimental protocol is also examined for the anionic dye Eriochrom Black-T (EBT). According to the results, a significant interaction between TiO 2 nanoparticles and EBT exist at pH 3, which is also well in accordance with reported higher efficiency of EBT degradation around pH 3. The elasticity measurements performed in this work, also support these results as an important characterization parameter for estimation of the molecular interactions in mixed adsorbed layers. [ABSTRACT FROM AUTHOR]

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.

Drop profile analysis tensiometry is applied to measure the dilational visco-elasticity of BLG at the buffered aqueous solution/tetradecane (W/TD) interface using oscillating drops of TD immersed in W at frequencies between 0.01–0.2 Hz. The buffered solutions were investigated at pH 3, pH 5 (isoelectric point) and pH 7 at different buffer concentrations (1 mM, 10 mM and 100 mM). The real part of the complex visco-elasticity shows a maximum when plotted as a function of the interfacial pressure Π. In contrast to the water/air surface (W/A) where we observe maximum elasticity values between 15 and 20 mN/m, at the W/TD interface these maximum values are up to 65–70 mM/m, which is in parallel with the much higher interfacial pressure values at the W/TD interface when compared to the W/A surface. [ABSTRACT FROM AUTHOR]

The adsorption of proteins (β-lactoglobulin, β-casein) and the oxyethylated non-ionic surfactants C 10 EO 8 and C 14 EO 8 at the aqueous solution/air interface is strongly enhanced and accelerated by the presence of hexane vapour in the air phase caused by the co-adsorption of hexane molecules. Due to this hexane co-adsorption, the dependence of dilational visco-elasticity modulus on surface pressure is shifted towards larger surface pressure values. The adsorption kinetics of the studied non-ionic surfactants shows the same picture as that observed for the two proteins. In contrast, the desorption process of the hexane molecules from a pre-adsorbed mixed adsorption layer is very slow. This decelerated desorption is explained by a rather large desorption energy required by the hexane molecules. The experimental data are compared with several theoretical models developed earlier. The results allow estimating the activation energy for the hexane desorption from adsorption layers of the two studied non-ionic surfactants. [ABSTRACT FROM AUTHOR]

Using drop profile analysis tensiometry the adsorption dynamics and the equilibrium equation of state of β-lactoglobulin (BLG) at the water/tetradecane (W/TD) interface are studied at pH 3, 5 and 7. The data are well described by a thermodynamic adsorption model using almost identical model parameters for all three pH values except for the surface activity coefficient. The surface pressure isotherms at the water/air (W/A) surface exhibit much steeper run than interfacial pressure at the W/TD interface for any of the studied cases at pH 3, 5 and 7, and the calculated adsorption isotherm data point at smaller adsorbed amounts for these pH. This seems to be in contrast to the much larger interfacial pressure changes reached at high BLG concentrations at the W/TD interface, which are almost three times higher than those at the W/A surface. The observations can be explained by a strong interaction between BLG and the oil molecules at the interface. The dynamic interfacial tensions can be adequately described by a mixed adsorption model, assuming a diffusional transport of the protein molecules in the aqueous bulk phase and an adsorption mechanism which assumes a change of the adsorption activity parameter in dependence of the interfacial coverage. [ABSTRACT FROM AUTHOR]

The adsorption kinetics of β-lactoglobulin (BLG) at the water/tetradecane (W/TD) interface as studied by drop profile analysis tensiometry is significantly controlled by the diffusional transport in the aqueous solution bulk. However, due to the contact with the hydrophobic oil phase the protein molecules change their conformation in order to adapt to the interfacial environment. This conformational change can be expressed via the adsorption activity constant. The analysis of the dynamic interfacial tensions leads to much lower activities at short adsorption times and low surface coverages. This allows to conclude that in the early stage of the adsorption layer formation the structure of the BLG adsorption layer at the W/TD interface is similar to that at the water/air (W/A) interface. [ABSTRACT FROM AUTHOR]

The surface tension of aqueous solution drops of ß-casein, ß-lactoglobulin, and human serum albumin at the interface to air and hexane saturated air are measured by drop profile analysis tensiometry. The results indicate that the dynamic and equilibrium surface tension for a hexane vapor atmosphere are considerably lower as compared to the values at the interface with pure air. The experiments are performed with the initial adsorption of protein followed by hexane adsorption, and with subsequent removal of hexane from the measuring cell after equilibrium is attained. Two models are proposed, both of which assume the diffusion of protein in the solution and either diffusion-governed or barrier-governed hexane coadsorption. The new developed theoretical equilibrium model assumes a double layer adsorption in these systems, with the first layer composed of protein mixed with hexane and the second layer formed by hexane molecules only. The experimental and calculated equilibrium surface tension data are in a perfect agreement. Note the model parameters are exactly the same as those found for the individual compounds. [ABSTRACT FROM AUTHOR]

The measured dynamic surface tension of a water drop in air saturated by heptane vapor shows a sharp decrease from about 60 mN m−1 to 40 mN m−1, and less after a certain adsorption time. The observed adsorption kinetics is analyzed by a theoretical model based on multilayer adsorption of alkanes from the vapor phase at the water surface. The model assumes a dependence of the kinetic coefficients of adsorption and desorption on the surface coverage and in equilibrium it reduces to the classical Brunauer–Emmett–Teller adsorption isotherm. The calculated time dependencies of adsorption and surface tension agree well with experimental data and predict a five-layer adsorption of heptane.

The surface tension and dilational surface visco-elasticity of the individual solutions of the biopolymer DNA and the azobenzene-containing cationic surfactant AzoTAB, as well as their mixtures were measured using the drop profile analysis tensiometry. The negatively charged DNA molecules form complexes with the cationic surfactant AzoTAB. Mixed DNA + AzoTAB solutions exhibit high surface activity and surface layer elasticity. Extremes in the dependence of these characteristics on the AzoTAB concentration exist within the concentration range of 3 × 10 −6 –5 × 10 −5 M. The surface tension of the mixture shows a minimum with a subsequent maximum. In the same concentration range the elasticity shows first a maximum and then a subsequent minimum. A recently developed thermodynamic model was modified to account for the dependence of the adsorption equilibrium constant of the adsorbed complex on the cationic surfactant concentration. This modified theory shows good agreement with the experimental data both for the surface tension and the elasticity values over the entire range of studied AzoTAB concentrations. [ABSTRACT FROM AUTHOR]

The drop profile method is used to study the influence of hexane vapor in the air atmosphere on the surface tension of water. It was shown that the results depend essentially on the air humidity. At the interface with dry air a fast and strong decrease of surface tension was observed. In humid air and in a measurement cell filled with water, the process is slower and the resulting surface tension is higher. The experimental conditions are defined at which stable results can be measured. A new theoretical model is developed to describe the influence of alkane vapor in the gas phase on the surface tension of aqueous solutions of the reorientable surfactant C 10 EO 8 . This model assumes that a first interfacial layer is composed by surfactants mixed with alkane, and a second layer which is formed by alkane only. The experimental equilibrium surface tension data for the studied C 10 EO 8 solutions agree very well with those calculated from the given model. [ABSTRACT FROM AUTHOR]

Janus emulsions, formed by mixing two oil components (i.e., olive oil (OO) and silicone oil (SiO)) with water in the presence of two surface active biopolymers, i.e., gelatin and chitosan, are investigated in more detail. The stability of Janus droplets formed strongly depends on the polymer components used. The mixture of both biopolymers represents an extraordinary effect which can be related to the complex formation of gelatin and chitosan. Taken into account that under the given pH conditions, in the acidic pH range between 4 and 6, below the isoelectric point of gelatin, both polymers are polycations, one can conclude that non-Coulombic interactions are of relevance for the enhanced surface activity of the complexes. Dynamic interfacial tension ( γ) measurements by using the drop profile analysis tensiometry (PAT) indicate a strong adsorption of the polymer complexes at the olive oil/water interface in contrast to the silicone/water interface. In a first step, the polymer complexes are adsorbed at the interface, and in a second step, a more rigid skin-like polymer layer is formed. This first example of a polymer-stabilized Janus emulsion opens new perspectives for the application, e.g., in food emulsions or for making scaffold materials. [ABSTRACT FROM AUTHOR]

Microencapsulation of vitamin E directly from oil-in-water (o/w) emulsions was carried out by means of a novel practically relevant approach. For the first time, a preformed polyelectrolyte–surfactant complex (sodium polystyrene sulfonate/dodecyl trimethyl ammonium bromide) was simultaneously used as an electrosteric emulsion stabilizer and as a charged precursor for the following build up of microcapsules. Subsequently, a layer-by-layer technique was applied to emulsions leading to the formation of core–shell microcapsules with oily cores and polyelectrolyte shells. The effect of the complexes on the process of emulsion formation and on the stability and characteristics of the resulting emulsions was investigated by measurements of dynamic and equilibrium interfacial tension, size distribution (DLS) and interfacial charge (zeta-potential). The resulting microcapsules were characterized by confocal laser scanning microscopy (CLSM), Cryo-SEM, size distribution and zeta-potential measurements on each stage of the shell assembly. The release kinetics of vitamin E was monitored during the consecutive steps of the encapsulation procedure using UV–vis spectroscopy and showed the progressive enhancement of sustainability. The developed approach may be promising for the practical use in the cosmetic and food industry. [ABSTRACT FROM AUTHOR]

Two oppositely charged surfactants in an aqueous solution interact with each other via electrostatic interactions and produce surfactant complexes-catanionics. However, their quantitative influence on the interfacial tension at the solution/air and solution/oil interfaces is still unknown. We have measured the interfacial tension of sodium dodecyl sulphate (SDS) and dodecyltrimethylammonium bromide (DoTAB) aqueous mixtures using the du Nouy ring tensiometer and drop profile analysis tensiometry (PAT-1). For the oil phase, we used hexane. The obtained kinetic and equilibrium experimental results were fitted with the common theoretical Frumkin adsorption model. We found that SDS + DoTAB complexes show much higher surface activity than the single surfactants. At solution/air and solution/oil interfaces, SDS and DoTAB produce ion pairs with low water affinity and relatively low oil solubility. SDS + DoTAB partition coefficient between hexane and water phases is 0.32. Such surfactant complexes with advanced surface characteristics may be beneficial in different industrial branches nowadays. [ABSTRACT FROM AUTHOR]

The equations of state, adsorption isotherms and functions of the distribution of protein molecules in liquid interfacial layers with respect to molar area and the equations for their viscoelastic behavior are presented. This theory was used to determine the adsorption characteristics of β-casein and β-lactoglobulin at water/oil interfaces. The experimental results are shown to be describable quite adequately by the proposed theory with consistent model parameters. The data analysis demonstrated that the β-casein molecule adsorbed at equilibrium conditions is more unfolded as compared with dynamic conditions, and this fact causes the significant increase of the adsorption equilibrium constant. The theory assumes the adsorption of protein molecules from the aqueous solution and a competitive adsorption of alkane molecules from the alkane phase. The comparison of the experimental equilibrium interfacial tension isotherms for β-lactoglobulin at the solution/hexane interface with data calculated using the proposed theoretical model demonstrates that the assumption of a competitive adsorption is essential, and the influence of the hexane molecules on the shape of the adsorption isotherm does in fact exist. [ABSTRACT FROM AUTHOR]

Oscillating drop tensiometry was applied to study adsorbed interfacial layers at water/air and water/hexane interfaces formed from mixed solutions of β-lactoglobulin (BLG, 1 μM in 10 mM buffer, pH 7 – negative net charge) and the anionic surfactant SDS or the cationic DoTAB. The interfacial pressure Π and the dilational viscoelasticity modulus | E | of the mixed layers were measured for mixtures of varying surfactant concentrations. The double capillary technique was employed which enables exchange of the protein solution in the drop bulk by surfactant solution (sequential adsorption) or by pure buffer (washing out). The first protocol allows probing the influence of the surfactant on a pre-adsorbed protein layer thus studying the protein/surfactant interactions at the interface. The second protocol gives access to the residual values of Π and | E | measured after the washing out procedure thus bringing information about the process of protein desorption. The DoTAB/BLG complexes exhibit higher surface activity and higher resistance to desorption in comparison with those for the SDS/BLG complexes due to hydrophobization via electrostatic binding of surfactant molecules. The neutral DoTAB/BLG complexes achieve maximum elastic response of the mixed layer. Mixed BLG/surfactant layers at the water/oil interface are found to reach higher surface pressure and lower maximum dilational elasticity than those at the water/air surface. The sequential adsorption mode experiments and the desorption study reveal that binding of DoTAB to pre-adsorbed BLG globules is somehow restricted at the water/air surface in comparison with the case of complex formation in the solution bulk and subsequently adsorbed at the water/air surface. Maximum elasticity is achieved with washed out layers obtained after simultaneous adsorption, i.e. isolation of the most surface active DoTAB/BLG complex. These specific effects are much less pronounced at the W/H interface. [ABSTRACT FROM AUTHOR]

The adsorption from mixed aqueous solutions of polyallyl amine hydrochloride (PAH)/sodium dodecyl sulphate (SDS), both in absence and presence of the inorganic electrolyte NaCl, at the solution/tetradecane interface is studied experimentally by drop profile analysis tensiometry. The results are discussed in terms of a competitive adsorption of PAH + SDS complexes and unbound SDS molecules. A thermodynamic model, developed originally for the adsorption of protein/surfactant mixtures, is modified such that it takes into account the formation of PAH + SDS complexes and the influence of the SDS concentration on their surface activity. It is shown that at low SDS concentrations the properties of the adsorbed monolayer are determined mostly by the adsorption of complexes, while at high SDS concentrations the properties are determined mostly by the SDS adsorption and the effect of the PAH + SDS complexes is negligibly small. The proposed modified model demonstrates good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hexane molecules adsorb from the vapour phase at the surfactant solution surface. [•] The presence of hexane enhances the C n TAB adsorption. [•] High C n TAB concentration, hexane molecules are removed from the adsorption layer. [•] Good theoretical fitting with a model for competitive adsorption of two components. [Copyright &y& Elsevier]

Abstract: The dynamic interfacial tension and dilational rheology of alkyltrimethylammonium bromides (C n TAB) solutions are studied for n =10, 12, 14 and 16 using drop profile analysis and capillary pressure tensiometry. The experimental data are analyzed on the basis of two theoretical models, the Frumkin Ionic Compressibility and the Langmuir Compressibility models [1]. We show that even the simplified Langmuir Compressibility model is able to adequately describe the dynamic properties of the investigated ionic surfactants. Dynamic experiments point out the difficulties related to short chain surfactants due to their very fast adsorption kinetics which cannot be studied with conventional tensiometer setups. [Copyright &y& Elsevier]

Abstract: The recently described new experimental tool called Drop and Bubble Micro Manipulator (DBMM) has been applied to studies of the stability of protein covered bubbles against coalescence. Among the available protocols the time interval between the moment of bubble contact to the moment of coalescence of two contacting bubble is determined for different β-Lactoglobulin (BLG) concentrations and different ageing times. A threshold concentration of BLG is needed to prevent immediate coalescence. The longer the ageing time above this threshold concentration of BLG is the longer is the lifetime of the liquid film between the bubbles. The adsorbed amount of BLG was determined as a function of time and concentration and correlates with the observed coalescence behaviour of the contacting bubbles. [Copyright &y& Elsevier]

Highlights: [•] C n TAB molecules adsorb from the water phase at the water/oil interface. [•] The presence of hexane phase enhances the C n TAB adsorption. [•] Lengths of the oil and surfactant molecules define the adsorption layer structure. [•] Good theoretical fitting is obtained with the Frumkin Ionic Compressibility model. [ABSTRACT FROM AUTHOR]

Abstract: The dilational rheology of liquid–air interfaces is very sensitive to the contents and composition of surface active molecules in the liquid. Therefore, these rheological quantities along with dynamic surface tension could prove suitable parameters for the diagnosis of certain deseases. The cerebrospinal fluid, expired air condensate and umbilical blood of newborns have been investigated for patients suffering from neurosyphilis and for a reference group for comparison. The visco-elasticity is measured by pendent drop analysis tensiometry with transient and harmonic surface area perturbations. It is shown that the dilational visco-elasticity parameters depend significantly on the disease, i.e. can be used as diagnostic tool. [Copyright &y& Elsevier]

Abstract: The displacement of mucin from the droplet simultaneously and sequentially was studied using drop profile analysis tensiometry (PAT-1) instrument equipped with special designed instrument to allow the bulk exchange of the droplet. The dynamic and equilibrium surface tension profiles were used to discuss the stability of the formed mixed surfactant–protein layer at the interface. The viscoelastic data also were used to determine the extent of protein at the interface. The results showed that the simultaneously formed surfactant–protein layer at the complex is more surface active than that formed sequentially. The results were discussed according different mechanisms describing the interaction between the protein molecules and the cationic surfactant. The study explained the antimicrobial activity of the studied surfactant in the biological field. [Copyright &y& Elsevier]

Abstract: The co-adsorption of hexane from the vapor phase and surfactants from an aqueous solution at the surface of drops are studied in dependence of surfactant concentration. For the anionic surfactant SDS as well as the cationic surfactant DoTAB a significant surfactant–hexane co-adsorption and a remarkable decrease in surface tension is observed. This hexane co-adsorption effect increases with surfactant concentration and reaches a maximum value at intermediate surfactant concentrations below the CMC values. Dynamic surface tension measurements by drop profile analysis tensiometry and calculation of the standard deviation from Laplacian shape fitting, demonstrate three different adsorption regions. The kinetics and equilibrium state of adsorption depend significantly on the surfactant concentration. For the initial effects (regular adsorption region) which appear quickly, a thermodynamic model is applied which is based on a mixed adsorption layer approach. [Copyright &y& Elsevier]

Abstract: Each experimental method has a certain range of application, and so do the instruments for measuring dynamic interfacial tension and dilational rheology. While the capillary pressure tensiometry provides data for the shortest adsorption times starting from milliseconds at liquid/gas and tens of milliseconds at liquid/liquid interfaces, the drop profile tensiometry allows measurements in a time window from seconds to many hours. Although both methods together cover a time range of about eight orders of magnitude (10−3 s to 105 s), not all surfactants can be investigated with these techniques in the required concentration range. The same is true for studies of the dilational rheology. While drop profile tensiometry allows oscillations between 10−3 Hz and 0.2Hz, which can be complemented by measurements with capillary pressure oscillating drops and the capillary wave damping method (up to 103 Hz) these six orders of magnitude in frequency are often insufficient for a complete characterization of interfacial dilational relaxations of surfactant adsorption layers. The presented analysis provides a guide to select the most suitable experimental method for a given surfactant to be studied. The analysis is based on a diffusion controlled adsorption kinetics and a Langmuir adsorption model. [Copyright &y& Elsevier]

Abstract: The adsorption behaviour of alkyl sulphates at the water/oil interface is rather different from that frequently studied at the water/air interface. First of all typical impurities in form of homologous alcohols, immanent for this type of surfactants at the surface of aqueous solutions, are not essential at the water/oil interface due to their high solubility in the oil phase. In the interfacial layers the oil molecules, here hexane, are incorporated into the structure, and have essential impact on the equation of state at low interfacial coverage and in particular at the shorter alkyl chain surfactants. For the longer chain alkyl sulphates (NaC14SO4 and NaC16SO4) and at high interfacial coverage the hexane molecules are squeezed out of the adsorption layer due to the stronger hydrophobic interaction between the surfactants’ alkyl chains. The adsorption characteristics are discussed in the framework of the two well-known thermodynamics Frumkin and reorientation models. [Copyright &y& Elsevier]

Abstract: Maximum bubble pressure and pendent drop profile analysis tensiometry are used to study the dynamic surface tension and rheological characteristics of saliva samples taken from volunteers of various sexes and age, and children with caries. The tensiometric characteristics of the secretions released by parotid, submandibular and sublingual glands are studied, and age-related and sex-related changes of some tensiometric characteristics of saliva are found. The differences are most essential for the tensiometric characteristics of saliva samples taken from caries-free children as compared with those taken from children with caries. Thus, the dynamic interfacial tensiometry is very sensitive and capable of providing information additional to the biochemical data about the properties of saliva, and could be recommended for the development of new diagnostic methods in dentistry. [Copyright &y& Elsevier]

The adsorption dynamics of silica nanoparticles (NP) and cetyltrimethylammonium bromide (CTAB) complexes is studied via dynamic surface properties characterization by the drop Profile Analysis Tensiometry (PAT). Considering the hypothesis that a nanoparticle with a certain number of attached surfactant molecules can be considered as a unified surface-active complex, the equilibrium surface tension for fixed CTAB/NP mixing ratios were considered to construct respective adsorption isotherms. The results can be well described by the Frumkin adsorption model. The fitting parameters of the Frumkin model for different mixing ratios demonstrate that complexes with higher mixing ratios occupy less space at the interface and show weaker interaction with each other. Also, the Ward and Tordai equation was fitted to the dynamic surface tension data for each ratio. The results show that by increasing the mixing ratio the adsorption of complexes tends toward a diffusion-controlled mechanism. On the other hand, for lower mixing ratios, the adsorption is affected by adsorption/desorption barriers so that a mixed diffusion-kinetic-controlled mechanism is recognized and discussed. Surfactant/NP ratio, the key parameter defining surface activity of the complexes [Display omitted] • Adsorption of Silica-CTAB complexes at air/water interface can be modeled at constant surfactant/nanoparticle ratio. • Frumkin Model is capable to predict the equilibrium surface tension of Silica-CTAB complexes. • Complexes with lower surfactant/nanoparticle ratios occupy more space at the interface. • Complexes with high surfactant/nanoparticle ratios illustrate a pure diffusion-based mechanism. • For low surfactant/nanoparticle ratios a mixed kinetic-diffusion behavior is observed. [ABSTRACT FROM AUTHOR]

Abstract: Drop profile analysis tensiometry is applied to study the adsorption dynamics of phospholipids, proteins and phospholipid/protein mixtures at liquid/liquid interfaces. Measurements of the dynamic interfacial tension of phospholipid layers give information on the adsorption mechanism and the structure of the adsorption layer. The equilibrium and dynamic adsorption of pure protein solutions, i.e. human serum album (HSA), β-lactoglobulin (β-LG), β-casein (β-CA), can be explained well by the thermodynamic model of Frumkin and the diffusion-controlled adsorption theory. The adsorption behavior from mixed phospholipid/protein solutions was also investigated in terms of dynamic interfacial tensions. Interestingly, a “skin-like” folded film of pure protein or phospholipid/protein complex layers can be observed at curved surfaces at the water/oil interfaces. The addition of phospholipids accelerates the formation of the folded structure at the drop surface through co-adsorption of proteins. [Copyright &y& Elsevier]

Abstract: Surfactants appear in multiphase fluid systems in which the interface and the adjacent bulk phase have been removed from equilibrium. Here, a new method is described for the measurement of rate constants of desorption of surface-active materials from fluid/fluid interfaces and the extent to which adsorption is reversible: the coaxial capillary pendant drop experimental technique. Kinetic constants are determined by desorption experiments in pendant drops in which the interface adjacent to a surfactant solution is removed from equilibrium by replacing the subphase of the drop with pure water. Further, we demonstrate that although the rate of subphase exchange is comparatively slow with respect to the desorption timescale, it is possible to resolve desorption processes which occur under local equilibrium with the adjacent bulk phase from those that are determined in part by sorption kinetics. Experiments which measure the desorption kinetic coefficient, α, using a homologous series of n-alkyl (C8, C10, C12, C14) dimethyl phosphine oxides are presented. [Copyright &y& Elsevier]

Abstract: Oscillating drop experiments with a drop profile analysis tensiometer provide the dilational elasticity and viscosity of surface layer. Model experiments for blood serum, composed of HSA and the non-ionic surfactant C14EO8, are used to demonstrate the theoretical approach for calculating the visco-elasticity of mixed adsorption layers from the adsorption characteristics of the single components. Experiments with real serum samples taken from patients choledocholithiasis-based benign obstructive jaundice before and after re-canalisation of the biliary tract demonstrate that the visco-elasticity of the respective adsorption layers is very sensitive of the successful surgery. [Copyright &y& Elsevier]