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The properties of adsorbed layers of protein fibrils differ significantly from the properties of fibril spread layers on an aqueous subphase. If the dependencies of the dynamic surface elasticity on surface pressure of Lysozyme (LYS) and β-lactoglobulin (BLG) aqueous dispersions proved to be close to the results for native protein solutions, LYS and BLG spread layers on the surface of 0.1 M NaCl solution exhibited the surface elasticity more than two times higher than the values for protein solutions with the same NaCl concentatration, presumably due to lower surface concentrations of hydrolysed peptides in the latter case. The properties of fibril spread and adsorbed layers and also their morphology, unlike the surface properties of protein solutions, depend noticeably on the ionic strength of the aqueous bulk phase. This dependence is stronger in case of LYS layers, which are also more prone to the formation of macroscopic and mesoscopic surface aggregates as compared with BLG layers.

This work is directed to the elucidation of the peculiarities of fullerene C60 interactions with bovine serum albumin (BSA) in mixed layers at the water-air interface. To this aim, the dilational surface elasticity was measured as a function of surface pressure and surface age and optical methods together with the atomic force microscopy (AFM) were applied. The dependencies of the dilational dynamic surface elasticity of the mixed C60/BSA layers on the surface pressure have two local maxima indicating a conformational transition in the layer. At low surface pressures (region of the first maximum) the surface properties are determined mainly by the protein, while in the second region of relatively high surface pressures the contribution of the fullerene is more important. The AFM images show that both C60 layers and mixed C60/BSA layers contain separate large fullerene aggregates with the length in Z-directions of up to 100 nm but the morphology of the regions between these aggregates differs for the two systems. The mixed layer contains some patches of a network of almost merged fullerene/protein aggregates with a length in Z-direction not longer than about 20 nm. The formation and the subsequent reorganization of the network lead to non-monotonic kinetic dependences of the dynamic surface elasticity in the course of protein penetration into the fullerene layer. The obtained results show strong interactions between the components in the surface layer and thereby can change the toxicity of the fullerene.

The interactions between fibrinogen and polyelectrolytes in the surface layer of their mixed solutions were studied by measurements of the dynamic surface tension and surface elasticity as a function of surface age, polyelectrolyte concentration and solution pH. A flexible and negatively charged polyelectrolyte − sodium polystyrolsulfonate (PSS) – influenced the kinetic dependencies of the surface properties both below and above the isoelectric point, where fibrinogen is positively and negatively charged, respectively, indicating the formation of protein/polyelectrolyte complexes. At the same time, the addition of a more rigid and positively charged polyelectrolyte – polydiallyldimethylammonium chloride (PDADMAC) – to fibrinogen solutions resulted in noticeable changes of the studied dynamic surface properties only at pH values higher than the isoelectric point, while at lower pH values no interactions between the two solutes were observed. The formation of the protein/polyelectrolyte complexes did not lead to noticeable changes of the protein tertiary structure in the surface layer and all the kinetic dependences of the dynamic surface properties were monotonic.

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.

The theoretical description of the adsorption of surfactants at interfaces between aqueous solutions and oil was based over a very long time on models derived for the solution/air interface. Thus, most of the experimentally observed peculiarities could not be specifically considered but were merely interpreted in terms of a penetration of oil molecules into the alkyl chain layer of the adsorbed surfactant molecules. These penetrating oil molecules enhance the surfactant adsorption as compared to the water/air interface. Later on, for the special situations at water/oil interfaces a competitive adsorption of surfactant and oil molecules was postulated, allowing a much better description of experimental data. This picture, however, was unable to explain why the interfacial tension of the water/oil interface decreases very quickly when extremely small amounts of surfactants are added to the water. This effect cannot be of competitive nature, but a cooperativity of surfactant and oil molecules forming a mixed adsorption layer is required instead. This cooperative effect means that already few surfactant molecules adsorbed at the interface can induce a significant ordering of oil molecules in the interfacial layer. This new interfacial structure, in turn, attracts further surfactant molecules to adsorb. Improving the theoretical description of experimental data was finally achieved by applying suitable adsorption models for the two adsorbing compounds, i.e. a Frumkin adsorption model for the oil molecules and a Langmuir, Frumkin, or reorientation model for the adsorbing surfactant molecules. Here, the progress in modelling surfactant adsorption at water/oil interfaces is discussed mainly for the homologous series of the cationic surfactants C(n)TAB, of the anionic surfactant SDS, and members of the homologous series of the non-ionic surfactants CnDMPO at water/alkane interfaces. (C) 2020 Elsevier B.V. All rights reserved.

The dynamic surface properties of solutions of pulmonary surfactant (PS) were investigated at various temperatures and in a broad range of surface tensions. The efficient dynamic surface elasticity was determined for the first time in case when the characteristic adsorption time is comparable with the period of surface area oscillations. The mechanical relaxation in the PS adsorption layer is accelerated strongly not only in the course of compression, but also in the course of expansion due to the formation of a sublayer. The harmonic oscillations of the surface area induce stationary oscillations of the surface tension if the characteristic adsorption time does not exceed the oscillation period and the sublayer formation is sufficiently fast. The information on the dynamic properties of the PS adsorption layer allows estimation of the PS efficiency in medical applications.

Polydopamine (PDA) films at the air - water interface can be easily obtained in slightly alkaline dopamine solutions using 02 dissolved in water as an oxidant but their insufficient stability limits their applications. In this work PDA films at the water surface were obtained by polymerization of dopamine hydrochloride (DA) by the enzyme laccase in a slightly acidic environment at a constant concentration of enzyme and DA concentrations in the range from 0.1 to 10 g/l. The dynamic surface elasticity, effective surface tension, film thickness and refractive index were measured as function of time to characterize the main steps of film formation. The obtained results show that laccase accelerates the polymerization process, decreases the required DA concentration for film formation, and insight from Brewster angle microscopy shows that laccase increases the resistance of the films to mechanical deformation. The dynamic surface elasticity of the obtained films is about seven times higher than the highest values for either pure PDA or pure laccase films. Laccase is inferred not only to provide crosslinking of the polymer but is also incorporated in the film resulting in its higher stability. The kinetic dependences of the surface properties allow the main steps of film formation to be distinguished: nucleation of polymer domains in a rapidly-formed protein film, coexistence of the protein and polymer domains, and their transformation into a highly dense composite film with encapsulated protein. Insight from atomic force microscopy images of films transferred to mica show that PDA fills in the gaps of spherical laccase aggregates when the DA concentration is increased and the film becomes less rough. The inclusion of laccase in PDA films significantly increases their stability.

In this work, dynamic surface properties of spread monolayers of DPPC and adsorbed layers of PS solutions were investigated in a broad range of surface pressure. Application of a modified Langmuir trough and a recently developed approach for the analysis of a non-linear response of the adsorption layer to large surface deformations gives a possibility to determine the dilational surface elasticity in the region of high surface pressures corresponding to the physiological state of the lung alveoli surface. Although DPPC is the main component of the complex pulmonary surfactant (PS) mixture, the dynamic surface properties of the adsorption layers of these two compounds are different. Other components in the PS adsorption layer lead to a decrease of the dynamic surface elasticity due to a looser packing of the layer, as confirmed by ellipsometry and infrared reflection absorption spectroscopy. Moreover, in the region of high surface pressures the main relaxation time of the surface stresses is much lower than that for spread DPPC monolayers. The fast relaxation in the adsorption layer can be connected with the redistribution of molecules between the surface and the subsurface layer in the course of compression. The acceleration of the relaxation processes can lead to a decrease of the number and size of collapsed parts of the layer and thereby to a decrease of the number of molecules with lost functional properties. This effect can be one of the reasons for the lower efficiency of synthetic pharmaceutical drugs, which do not have proteins in their composition, as compared with the natural PS extracted from animal lungs.

The interfacial tension response to dilational deformation of interfacial area exhibits a (more or less) nonlinear behavior, depending on the amplitude of the deformation. Studies of such observable interfacial properties in the nonlinear domain suggest valuable information about the two-dimensional microstructure of the interfacial layer, as well as about the structure time-evolution. In this article, the emphasis is centered on the available mathematical methods for quantitatively analyzing and describing the magnitude and the characteristics of the nonlinear interfacial viscoelastic properties. Specifically, in periodic oscillation experiments the nonlinear behavior can be represented by the combination of a linear part (the surface dilational modulus), with an additional complementary Fourier analysis parameterizing the nonlinearity. Also asymmetric Lissajous plots, of interfacial tension versus deformation, are useful tools for expanding the response nonlinearity into four distinct components relevant to significant points of the cyclic loop. In connection with the mathematical methods, nonequilibrium thermodynamic formulations provide a powerful theoretical framework for investigating the interfacial dynamic properties of multiphase systems. Experimental results for adsorption layers of complex components, available in the literature, show notable nonlinear interfacial viscoelastic behavior. In particular in this review, data are illustrated for solutions of polymers and of polyelectrolyte/surfactant complexes. The observed nonlinear findings reveal formation of complexes, patches, and other different interfacial structures.

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.

The non-monotonic concentration and kinetic dependencies of the dynamic dilational surface elasticity of mixed poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate(SDS)/NaCl solutions indicate the formation of micro-aggregates in the surface layer. The increase of the solution's ionic strength results in strong changes of the surface dilational rheological properties and thereby of the interfacial layer structure at lower SDS concentrations due to the large increase of the adsorption rate. Close to the charge match point of the components, however, the rheological properties are influenced by the presence of micro-aggregates embedded in the adsorption layer. In this case, effects of changing the sample history on the rheological behavior and heterogeneity of the interface were further investigated.

The surface properties of a polydopamine layer at the air-water interface were studied by dilatational surface rheology, ellipsometry and Brewster angle microscopy (BAM). A significant increase of the dynamic surface elasticity was discovered when the concentration changed from 0.75 g/l to 2 g/l with the maximum value of about 60 mN/m at a concentration of 1 g/l. The obtained results indicate that the surface film consists of separate domains and the high surface elasticity is a consequence of the interactions between relatively rigid domains of the polymer film. This conclusion was confirmed by Brewster angle microscopy, which demonstrated different steps of the polydopamine film growth. Separate domains appeared at the first step while one can observe a continuous film close to equilibrium. An increase of the initial concentration led to faster polymerization and to the formation of a thicker film. The dynamic surface elasticity decreased in the concentration range from 2 g/l to 5 g/l when the thickness of the polymer film reached about 80 nm. In this case the film could be destroyed in the course of deformation. The cracks in the film resulted in a decrease of the dynamic surface elasticity.

The presented drop and bubble micro manipulator (DBMM) is a new experimental tool for the quantitative analysis of the interaction between two drops or two bubbles or even between a single drop with a bubble in a liquid medium. For each drop or bubble, a coarse and a very fine dosing system allow controlling their size or changing it in respect to a given protocol. An accurate pressure sensor for each drop/bubble can record changes in the capillary pressure with a selected sampling rate in order to follow critical processes between the two liquid menisci, such as coalescence. The stability of liquid films between drops or bubbles can be studied also under external perturbations, i.e. a harmonic oscillation with a given frequency and amplitude can be generated in order to find critical conditions for the coalescence. The described tool can be used in different experimental protocols. Among them there are options to mimic the situation of multilayers and multiple emulsions. Recording of dynamic processes as video with a standard frame rate is possible as well. Alternatively, a fast video camera can be mounted to monitor fast processes, such as the coalescence of two drops or bubbles.

The dilational surface rheology is applied to solutions of globular proteins (bovine serum albumin and β-lactoglobulin) in presence of urea. The kinetic dependencies of the dynamic dilational surface elasticity become non-monotonic if the denaturant concentration exceeds a certain critical value indicating the adsorption of unfolded protein molecules. The unfolding in the surface layer occurs at lower urea concentrations than in the bulk phase similar to the case of mixed solutions of the proteins and guanidine hydrochloride. At the same time, the influence of urea on the dilational surface rheological properties of protein solutions has some peculiarities. In particular, the high values of the dynamic surface elasticity close to equilibrium indicate the limited flexibility of unfolded BLG molecules in the surface layer.

Measurements by capillary pressure tensiometry, under microgravity conditions aboard the International Space Station, supplied a consistent set of reliable results for the dynamic interfacial tension and for the interfacial dilational viscoelastic modulus, quantitatively characterizing the dynamics of Span-80 adsorbed layers at the paraffin-oil/water interface. The experiments were executed at three different temperatures, i.e., 20, 30 and 40 °C, according to a pre-established built-in time-line in the orbiting facility. The interfacial area was subjected to perturbations with various functional forms (square pulses, ramps and harmonic oscillations), at three consecutive amplitudes (5%, 10% and 20%). Each experiment was performed in three successive repetitions, in view of an advantageous telemetered data redundancy. The interfacial responses to imposed perturbations, for the studied minimal surfactant concentration of Span-80 in paraffin-oil (that is (2 ÷ 3) × 10−5 mol/dm3) revealed a diffusion-controlled adsorption mechanism, definitely matching the Lucassen & Van den Tempel model in the frequency-domain representation. The interfacial responses also showed a linearity range up to the 20% amplitude. Interfacial relaxation responses to transient interfacial perturbations substantially validated the diffusion-controlled model for the adsorption mechanism, in the time-domain representation.

The oscillating drop and bubble analyzer (ODBA) is an experimental set-up based on the measurement of capillary pressure under static and dynamic conditions. It allows studies of slow and fast dynamic surface and interfacial tensions, following different growing and oscillating drop or bubble protocols, as well as determination of the dilational interfacial visco-elasticity of liquid interfacial layers. For the visco-elasticity studies, drops or bubbles are subjected to harmonic oscillations of area or volume in a broad frequency range, and the resulting harmonic capillary pressure response is analyzed by Fourier analysis. Also, transient relaxations can be easily performed, which are of particular importance for isodense systems. The limits of applicability for highly dynamic conditions are given by the hydrodynamics of the fluid flow inside the capillary tip and the pressure cell which depend on fluid properties, capillary tip size, and geometry. For the growing drop protocol, additional phenomena during drop formation and detachment play a significant role. For oscillating drops or bubbles, the highest accessible frequencies also depend on the absolute drop size and applied oscillation amplitude. In this work, the capability of the technique for measurements in the frequency range between 1 and 100 Hz are discussed, and elasticity values at up to 80 Hz were measured for the liquid–liquid interface.

Recent application of the methods of surface dilational rheology to solutions of the complexes between synthetic polyelectrolytes and oppositely charged surfactants (PSC) gave a possibility to determine some steps of the adsorption layer formation and to discover an abrupt transition connected with the formation of microaggregates at the liquid surface. The kinetic dependencies of the dynamic surface elasticity are always monotonous at low surfactant concentrations but can have one or two local maxima in the range beyond the critical aggregation concentration. The first maximum is accompanied by the generation of higher harmonics of induced surface tension oscillations and caused by heterogeneities in the adsorption layer. The formation of a multilayered structure at the surface for some systems leads to the second maximum in the dynamic surface elasticity. The hydrophobicity and charge density of a polymer chain influence strongly the surface structure, resulting in a variety of dynamic surface properties of PSC solutions. Optical methods and atomic force microscopy give additional information for the systems under consideration. Experimental results and existing theoretical frameworks are reviewed with emphasis on the general features of all studied PSC systems.

The dynamic dilatational surface elasticity of mixed solutions of globular proteins (β-lactoglobulin (BLG) and bovine serum albumin (BSA)) with cationic (dodecyltrimethylammonium bromide (DTAB)) and anionic (sodium dodecyl sulfate (SDS)) surfactants was measured as a function of the surfactant concentration and surface age. If the cationic surfactant concentration exceeds a certain critical value, the kinetic dependencies of the dynamic surface elasticity of BLG/DTAB and BSA/DTAB solutions become nonmonotonous and resemble those of mixed solutions of proteins with guanidine hydrochloride. This result indicates not only the destruction of the protein tertiary structure in the surface layer of mixed solution but also a strong perturbation of the secondary structure. The corresponding kinetic dependencies for protein solutions with added anionic surfactants are always monotonous, thereby revealing a different mechanism of the adsorption layer formation. One can assume that the secondary structure is destroyed to a lesser extent in the latter case and hinders the formation of loops and tails at the interface. The increase of the solution's ionic strength by the addition of sodium chloride results in stronger changes of the protein conformations in the surface layer and the appearance of a local maximum in the kinetic dependencies of the dynamic surface elasticity in a relatively narrow range of SDS concentration.

Scanning probe microscopy is used to study adsorption films of sodium polystyrenesulfonate/dodecyltrimethylammonium bromide complexes, which are transferred from aqueous solution surfaces to the mica surface by the Langmuir-Blodgett method. It is established that the results obtained at surfactant concentrations below critical micelle concentration agree with the conclusions on the structure of the films dased on the data of the dilatational surface rheology (Noskov, B.A., Loglio, G., Miller, R., J. Phys. Chem. B, 2004, vol. 108, p. 18615). At low concentrations of the low-molecular-mass surfactant, a thin adsorption film containing a large number of holes is formed on the surface of an aqueous solution. As the surfactant concentration is increased to reach the region of a dramatic reduction in the dynamic surface elasticity, the morphology of the film drastically changes; i.e., dense three-dimensional aggregates are formed on the solution surface.

The dilational dynamic surface elasticity of mixed aqueous polyvinylpyridinium chloride/sodium dodecyl sulfate solutions (PVPmCl/SDS) was measured as a function of time and surfactant concentration. This system represents a typical example of polyelectrolyte/surfactant complex formation and subsequent aggregation on the nano-scale. The concentration dependence of the real part of the dynamic surface elasticity for the mixed PVPmCl/SDS solutions in 0.1 M NaCl and without added NaCl qualitatively agreed with the corresponding results for some previously studied polyelectrolyte/surfactant solutions. This similarity indicates that strong changes of the surface visco-elasticity in a narrow concentration range can be explained by the formation of microparticles in the surface layer. The addition of 0.1 M NaCl to PVPmCl/SDS solutions led to an almost two times decrease of the surface elasticity at low concentrations and to the acceleration of the adsorption layer formation. At the same time the imaginary part of surface elasticity of PVPmCl/SDS solutions was significantly higher than the corresponding results for the earlier studied systems and the adsorption layers proved to be visco-elastic in a broad concentration range. The application of the Maxwell rheological model in this case allowed the calculation of the main relaxation time. The main relaxation process is the surfactant exchange between the surface layer and the bulk phase or in the surface layer between free surfactant molecules and those bound in aggregates. The distinction of the surface visco-elasticity of PVPmCl/SDS solutions from the previously studied systems can be explained by the lower stability of polyelectrolyte/surfactant complexes in the adsorption layer.

In this article a technique that allows derivation of the conversion matrix of a two-port device using a measurement setup based on a nonlinear vector network analyzer (NVNA), which is capable of identifying the optimum local oscillator (LO) level and the corresponding RF and IF terminations for a microwave mixer, is discussed and validated. This technique is applied to extract the conversion matrix of gate-pumped 0.2-μm pseudomorphic high-electron-mobility transistors (PHEMTs) driven by a 4.8-GHz signal at different power levels and using an intermediate frequency of 600 MHz. Several experimental results provide a behavioral description of the up- and down-conversion mechanism in microwave mixers and highlight the dependency of the conversion-matrix coefficients on the pumping signal amplitude and phase. Detailed validation of this technique is provided by means of a circuit-level simulation and its consistency by vector network analyzer (VNA) measurements. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.

The dynamic surface elasticity of mixed aqueous poly(styrenesulfonate)/alkyltrimethylammonium bromide solutions has been measured by the oscillating barrier, oscillating drop, and capillary wave methods as a function of time and surfactant concentration. At low surfactant concentrations ( 2 mM) the modulus of the dynamic surface elasticity is low and the adsorbed film is viscoelastic.

Measurements of the dilational dynamic surface elasticity allow determination of some distinctions between the properties of monolayers of charged polystyrene nano- and microparticles at the water/air and water/oil interfaces. For example, the surface elasticity at the water/oil interface is lower and does not depend on the solution's ionic strength unlike the case of water/air interface. The obtained results at relatively low surface pressures (

This short review is devoted to recent achievements in studies of the dilational surface rheological properties of the systems containing complexes of silica nanoparticles with conventional surfactants. It is shown that there is a surfactant concentration range where the dynamic surface elasticity reaches extremely high values up to 1000 mN/m. This result can explain the formation of very stable foams and emulsions containing nanoparticles. In some surfactant concentration ranges the adsorption layer is characterized by a non-linear response to small compressions or expansions of the liquid surface. Possible causes of this behavior and the mechanism of main relaxation processes are briefly discussed. © 2014 Pleiades Publishing, Ltd.

The surface rheological behaviour of spread monolayers of DPPC (L-α-dipalmitoyl phosphatidyl chinoline) and DMPE (L-α-dimyristoyl phosphatidyl ethanolamine) on water has been investigated under shear and dilation/compression deformation. Harmonic area perturbations are performed using an oscillating barrier method which provides information on the monolayer dilational elasticity and the relaxation processes happening in the monolayers as a function of surface pressure. A surface shear rheometer has been used to measure the surface shear viscosity and elasticity of the same monolayers. The shear and dilational rheological properties can be explained by the morphology of the phospholipid monolayers as a function of surface pressure.

The adsorption films of silica nanoparticles modified by a cationic surfactant (cetyltrimethylammonium bromide, CTAB) at the air-water interface were investigated by the dilational surface rheology and optical methods. Special attention was paid to the slow changes of surface properties with the surface age. The surface tension and dynamic dilational surface elasticity were measured as a function of CTAB concentration. The whole surfactant concentration range can be divided into four regions characterized by different surface rheological behavior. Depending on the CTAB concentration, the surface elasticity close to the equilibrium may reach extremely high values ([similar]1000 mN m-1) and strongly depends on the applied surface strain. This occurs at surfactant concentrations below the region where the dispersion becomes turbid, indicating particle aggregation in the bulk. The Brewster angle microscopy and ellipsometry show that the adsorption layer becomes fragile and inhomogeneous in this region.

The dynamics of liquid interfaces is of eminent importance for many modern technologies. The production and storage of foam and emulsion products is a prominent example where liquid interfaces are for example freshly formed and expanded (foaming, emulsification) or compressed (coalescence, Ostwald ripening). A quantitative knowledge of the dynamics of liquid interfacial layers provides an excellent starting point for tailoring formulations for the optimization of technologies. Various experimental techniques combined with quantitative theoretical models represent an efficient toolbox to meet the requirements in practice. The Maximum Bubble Pressure Tensiometry (MBPT), known for more than 150 years, has been developed mainly during the last 20 years as method for dynamic surface tensions of surfactant solutions and can be called now the World Champion in terms of shortest adsorption times. MBPT allows getting experimental data down to 100 ?s and in this way gives insight into the fast formation of adsorption layers especially for concentrated solutions. Beyond the CMC of a surfactant the experimental data even allow analyzing the mechanism of micelle formation and dissolution kinetics. Tensiometry methods based on the profile of drops and bubbles (PAT) are at present the work horses in all interfacial laboratories. Its triumphal march was founded mainly by the availability of electronic video cameras and frame grabbers, used via computers. While in the beginning, powerful workstations were needed to cope with the huge amount of data, nowadays even laptops equipped with a webcam are suitable for practicing this methodology. Fully automatic instruments exist on the market which give access to various types of investigations, not only of the adsorption of surfactants at a drop or bubble surfaces of fixed surface area. Computer controlled dosing systems provide additional protocols, such as generation of transient or harmonic perturbations, or even real time drop volume exchange to study the adsorption of different surface active compounds in a sequential way.

The direct interaction between two droplets or two bubbles represents an important elementary process in foams or emulsions. The knowledge about the stability of the film between them is essential to prevent coalescence. There are not many tools known in literature which allow to study this [1]. We present a drop and bubble micro manipulator (DBMM) as a new experimental tool for the quantitative analysis of the interaction between two drops or two bubbles, or even between a single drop and a single bubble, in a liquid medium. For each drop or bubble, a coarse and a very fine dosing system exists in order to control their size or change it in respect to a given protocol. Accurate pressure sensors for each drop/bubble allow to record changes in the capillary pressure and also to detect coalescence [2]. The DBMM also allows to study the stability of liquid films between drops or bubbles under the effect of external perturbations, i.e. a harmonic oscillation with a given frequency and amplitude can be generated in the drops/bubbles in order to find critical conditions for the coalescence. The instrument can be equipped with a fast video camera in order to monitor fast processes such as the coalescence. Situation at the tip of two oppositely positioned capillary tips: a) two hexane droplets in water; b) two air bubbles in water; c) hexane droplet (left) and air bubble (right) in water As an example of application, the instrument is used to quantify the stability between protein covered oil droplets in an aqueous medium and to demonstrate how the addition of low molecular surfactants can change the coalescence behavior. References [1] S. Ata, J. Colloid Interface Sci. 338, 558 (2009) [2] G.Loglio, P.Pandolfini, F.Ravera, R.Pugh, A.V.Makievski, A.Javadi and R.Miller, Experimental Observation of Drop-Drop Coalescence in Liquid-Liquid Systems: Instrument Design and Features, in "Bubble and Drop Interfaces", Vol. 2, Progress Colloid Interface Sci., R. Miller and L. Liggieri (Eds.), Brill Publ., Leiden, p. 384, (2011).

A new methodology, based on fundamental optical principles relevant to the evanescent wave properties, is developed to evaluate the thinning behavior and the local thickness in different positions for curved aqueous emulsion films, generated in a hydrocarbon matrix. This methodology is applied to test data obtained by a specially-designed bread-board cell. The generated films, constituted by an aqueous sodium dodecylsulfate solution at concentration c = 2.5 times the critical micellar concentration, remain stable during several hours. The results show a slow evolution of the film thickness as a function of time starting from micrometric dimension, at the initial film formation, to a few nanometres prior to film breakage. The action of the gravitational drainage is furthermore assessed by the local thickness values in different positions of the film profile. The illustrated examples demonstrate that the evanescent wave effect can be advantageously adopted as a complementary measurement technique, additional to the usual interferometric technique.

Rheological data of the marine surface obtained from frequency wave spectra are compared with physico-chemical analyses of water samples drawn simultaneously from half a meter below the interface in fifteen preselected locations along a stretch of Tuscan Coast located between the Arno and Serchio rivers. The study has proved the presence of adsorption films tightly related to the rivers' plumes. A good correlation between the anionic surfactants detected in gas-bubble-enriched samples and the adsorbent excess measured at the surface has been observed. Implications of the multifrequency radar remote-sensing technique are here discussed.

This paper considers the importance of marine aerosol in the atmosphere. As a consequence of its peculiar generation mechanism, it is also considered as a possible contributor to the transport of man-made microcomponents via air-sea interaction, especially in remote sites. In view of future marine aerosol studies, the dominant presence of marine aerosol components in coastal Antarctic snow is discussed the presence of fluorescent marine organic matter in Antarctic snow is shown. Its “marum” nature is evidenced. We give a tentative interpretation of the experimental data, and make a hypothesis concerning the variations in marine aerosol composition in correspondence to various altitudes.

The physico-chemical properties of liquid films, which determine their stability in time and against perturbations, are quite directly related to the properties of the corresponding emulsions and foams [1]. Studying these properties is then important to establish quantitative models useful to setup products and processes in the field of foams and emulsions. Microgravity can be a particularly effective environment where the physico-chemical characteristics of liquid films can be investigated. In fact the thinning and destabilisation of the liquid-film is driven by two major drainage processes, by capillarity and gravitational forces, respectively. The latter can be strongly attenuated by weightlessness, allowing for investigating the film thinning as subjected to capillarity alone. The experiment LIFT (Liquid-Film Tensiometer), supported by the Italian Space Agency, is conceived to investigate the dynamic properties of the film by means of a specific tensiometric technique, developed in the field of Capillary Pressure Tensiometry [2]. Such technique, already implemented in the ESA facility FASTER (Facility for Adsorption and Surface TEnsion Research) for Columbus EDR, was already shown to be very suitable to study single liquid interfaces under microgravity. LIFT is in fact being designed to be housed inside the facility FASTER. LIFT allows the dynamic tension of liquid films to be measured during its evolution and/or drainage via capillary pressure method as well as its thickness by means of an advanced interferometric technique. Moreover being this technique also appropriate for measuring the response of the film tension to perturbations of its interfacial area, investigations of the film dilational rheology can be performed, which are particularly relevant for emulsion and foam studies. The present contribution is aimed at providing an overview of the LIFT programme, giving a description of the techniques to be utilized and of the planned experiments and reporting some results obtained with the laboratory prototypes. References: [1] Y.H. Kim, K Koczo, D. T. Wasan, J. Colloid Interface Sci.,187 (1997) 29 [2] V.I. Kovalchuk; J. Krägel, A.V. Makievski, F. Ravera, L. Liggieri, G. Loglio, V.B. Fainerman, R. Miller, J. Colloid Interface Sci., 280 (2004) 498

Measurement of dynamic interfacial tension and estimation of dilational viscoelasticity parameters is an important request for process designing and optimization in multiphase flow systems, such as in foams and emulsions, extraction, mixing and separation, spraying and particle technology, bubble columns and bioreactors, and microencapsulation in biomedical engineering. However for fast dynamic conditions, crucial for many practical applications, formation and control of interfaces and simultaneously measurement of basic parameters, such as interface contour and capillary pressure, is very difficult and requires special tools. The measurement tools should have a sufficiently high sensitivity, without getting strongly affecting from any types of perturbations. This is why the development of measurement tools like capillary pressure techniques for fast dynamic conditions needs enormous efforts from a theoretical basis and practical application point of view. The basis of this methodology has been described during the last decade and the method has been used for many systems. However for fast dynamic conditions the experimental technique is still under development and needs improvement in hardware, software, experimental protocols and data analysis [1, 2]. The main objective of the presented research is comparison of the performance of two different experimental setups (CPT and ODBA), the corresponding experimental protocols and data analysis. This includes the estimation of the hydrodynamics contribution, compressibility and noise effects on the measured total pressure during growing/oscillating bubble/droplet experiments. References. [1] A. Javadi, J. Krägel, P. Pandolfini, G. Loglio, V.I. Kovalchuk E.V. Aksenenko, F. Ravera, L. Liggieri and R. Miller, Colloids and Surfaces A: 365 (2010) 62-69 [2]F. Ravera G. Loglio, P. Pandolfini, E. Santini, L. Liggieri, Colloids and Surfaces A: 365 (2010) 2-13. Corresponding author: aliyar.javadi@mpikg.mpg.de

Investigating adsorption and dilational properties at liquid-fluid interfaces is relevant for a vast number of natural processes and technological applications. Among them, most important are systems involving composite interfacial layers containing, for example, mixture of different surface active compounds and/or solid nanoparticles. The study of dilational rheology, especially for composite systems, has been proven to be one of the most effective tool to obtain qualitative and quantitative information about the structural features and the kinetic processes in interfacial layers [1]. To exploit the high potentialities of this kind of investigation it is important, from one side, to rely on experimental methods for an accurate measurement of the interfacial viscoelasticity and, on the other side, the development of theoretical models allowing for the extraction of the maximum of information on the mechanisms at the bases of the dynamic features of the interfacial layers. From the experimental point of view, during last years methodologies based on the analysis of the interfacial tension response to controlled harmonic oscillations of the interfacial area of bubbles and drops have been developed [2] which allows for the characterisation of the rheological properties of the interfacial layer in a quite broad range of characteristic time. These methods have been applied to several surfactant systems containing nanoparticles as well. Classical theoretical models for dilational rheology have been used for the interpretation of the experimental data and some times especially for composite monolayers extension of them were required. Aim of this contribution is to give an overview of recent results in the field of dilational rheology of mixed surfactant - nanoparticle layer obtained by using new interpretative approaches. Some recent results in the field of the theoretical models for dilational rheology will be presented, especially developed to interpret the dilational viscoelasticity of mixed surfactant-nanoparticle interfacial layers. References 1. Miller, R.; Liggieri, L., Interfacial Rheology, Brill, 2009. 2. Ravera F., Loglio G., Kovalchuk V.I, Current Opinion in Colloid & Interface Science 15 (2010) 217-228

Measurements of the surface dilational elasticity close to equilibrium did not indicate significant distinctions in the surface conformation of different forms of bovine serum albumin (BSA) in a broad pH range. At the same time, the protein denaturation in the surface layer under the influence of guanidine hydrochloride led to strong changes in the kinetic dependencies of the dynamic surface elasticity if the denaturant concentration exceeded a critical value. It was shown that the BSA unfolding at the solution surface occurred at lower denaturant concentrations than in the bulk phase. In the former case, the unfolding resulted in the formation of loops and tails at surface pressures above 12 mN/m. The maximal values of the dynamic surface elasticity almost coincided with the corresponding data for the recently investigated solutions of β-lactoglobulin, thereby indicating a similar unfolding mechanism.

The Capillary Pressure Tensiometry is an effective technique for dilational rheological investigations when it is used according to the oscillating drop/bubble method. This method allows for an indirect determination of the dilational viscoelasticity versus frequency through the acquisition of the pressure signal obtained as response to harmonic perturbations of the drop/bubble interfacial area. A critical aspect of this technique concerns the calculation of the real and imaginary part of the dilational viscoelasticity from the directly acquired experimental data. Such calculation requires a specific experiment theory accounting also for the compressibility of the closed part of the experimental cell and for the fact that the acquired pressure is a superposition of different fluid dynamic contributions. Here we present an extension of previously proposed approaches, considering two different CPT configurations which refer to some already in use. The pressure inside the measurement cell is theoretically calculated considering the contributions, not only of the capillary pressure, but also of the Poiseuille pressure due to the fluid motion through the capillary and of hydrodynamic inertial terms. Simulations of experimental pressure signal are calculated as a function of specific experimental parameters in order to evaluate their influence on the measurement and to improve the effectiveness of the apparatus and the experimental methodology. Moreover in order to validate the assumptions of this approach, specifically acquired experimental data are analysed.

Theoretical models of the exchange of matter at interfaces are necessary to interpret relaxation phenomena in surfactant adsorption layers. For liquid-liquid systems, the diffusion-controlled exchanges of surfactant molecules at the interfaces can be influenced by a simultaneous transfer of molecules from one bulk phase to the other. The diffusional mass exchange function is derived taking into account the transfer across the interface. The resulting mass exchange function is used to calculate the interfacial tension response of a liquid-liquid system. As an example, the interfacial response after a ramp-type area perturbation is calculated.

The functional form of the surface dilational modulus is determined by considering the subsurface concentration changes produced by the diffusion process consequent to a non-periodic (rectangular step) perturbation of surface area (local equilibrium between surface and subsurface is assumed). The mathematical treatment is intended to present a straightforward demonstration that the same (unique) physical quantity, i.e. the dilational modulus, governs both harmonic and transient surface processes. The results definitely show that this modulus is an intrinsic physical property of a diffusive system, independent of the type of surface disturbance (within the linearity approximation).

The trapezoidal pulse perturbation is shown to be an attractive procedure for the measurement of dynamic properties of fluid—fluid interfaces. The surface response characterizes the surface relaxation behavior well. Theoretically, this procedure has foundations within the framework of linear non-equilibrium thermodynamics. From the experimental point of view, the procedure offers the possibility of checking the experimental reliability and exhibits practical aspects due to the short duration of the surface response. Benefits are also evident in data processing.