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Advances in Colloid and Interface Science (v.117, #1-3)
The role of interactions in defining the structure of mixed protein–surfactant interfaces by Alan Mackie; Peter Wilde (pp. 3-13).
The behaviour of dispersed systems is often controlled by the composition of the interface between the different phases. Because of the inherent differences between proteins and surfactants, when both are present at the interface complex pseudo two-dimensional structures can be formed. This review brings together work that allows these structures to be explained in terms of the interactions involved. The significance of both the interactions and the structures is discussed in terms of the effect on bulk properties in colloidal systems.
Keywords: Protein; Surfactant; Interactions; Interface; Structures
Oxygen tensioactivity on liquid-metal drops by E. Ricci; E. Arato; A. Passerone; P. Costa (pp. 15-32).
The influence of oxygen on the surface tension of liquid metals is a topic of undoubted interest as the formation of oxide films, or even oxygen contamination of the metal interface, represents the main source of error in determining the surface tension. The evaluation of gas–atmosphere mass exchanges under stationary conditions allows the evaluation of an effective oxygen pressure at which the oxidation of metal becomes evident. This effective oxygen pressure can be considered as a property of the system and, according to experimental evidence, can be many orders of magnitude greater than the equilibrium pressure. The measurement of the surface tension is a good way of studying interface properties, their temporal change and their connections to transport and reaction rates. This paper represents a review of a work undertaken with the aim of understanding oxygen mass transport at the liquid metal surface in relation to the study of capillary phenomena at high temperature.
Keywords: Metal oxidation; Interface saturation; Transport phenomena; Surface tension; Dynamic measurements
Interfacial properties of pulmonary surfactant layers by R. Wüstneck; J. Perez-Gil; N. Wüstneck; A. Cruz; V.B. Fainerman; U. Pison (pp. 33-58).
The composition of the pulmonary surfactant and the border conditions of normal human breathing are relevant to characterize the interfacial behavior of pulmonary layers. Based on experimental data methods are reviewed to investigate interfacial properties of artificial pulmonary layers and to explain the behavior and interfacial structures of the main components during compression and expansion of the layers observed by epifluorescence and scanning force microscopy. Terms like over-compression, collapse, and formation of the surfactant reservoir are discussed. Consequences for the viscoelastic surface rheological behavior of such layers are elucidated by surface pressure relaxation and harmonic oscillation experiments. Based on a generalized Volmer isotherm the interfacial phase transition is discussed for the hydrophobic surfactant proteins, SP-B and SP-C, as well as for the mixtures of dipalmitoylphosphatidylcholine (DPPC) with these proteins. The behavior of the layers depends on both the oligomerisation state and the secondary structure of the hydrophobic surfactant proteins, which are controlled by the preparation of the proteins. An example for the surface properties of bronchoalveolar porcine lung washings of uninjured, injured, and Curosurf treated lavage is discussed in the light of surface behavior. An outlook summarizes the present knowledge and the main future development in this field of surface science.
Keywords: Pulmonary surfactant; Surface behavior; Phospholipids; Surfactant protein
Morphology characterization of emulsions by differential scanning calorimetry by D. Clausse; F. Gomez; I. Pezron; L. Komunjer; C. Dalmazzone (pp. 59-74).
This article is a review of some results obtained by Differential Scanning Calorimetry (DSC) for characterizing the morphology of emulsions. In a classical DSC experiment, an emulsion sample is submitted to a regular cooling and heating cycle between temperatures that include freezing and melting of the dispersed droplets. By using the thermograms found in the literature for various emulsions, how to get information about the solidification and melting, the presence of solute, the emulsion type, the transfer of matter, the stability and the droplet size is shown.
Keywords: Emulsion; DSC; Freezing; Melting; Mass transfer; Stability; Droplet size
Influence of surface processes on the dilational visco-elasticity of surfactant solutions by Francesca Ravera; Michele Ferrari; Eva Santini; Libero Liggieri (pp. 75-100).
The mechanical properties of liquid–fluid systems, like the dynamic interfacial tension and interfacial rheology are closely related to the kinetic processes involved and to the behaviour of the adsorbed molecules. Therefore, provided suitable models and experimental methods are set, investigating these properties allows qualitative and quantitative information on these processes to be drawn.This paper presents recent developments in dilational rheology of liquid–fluid adsorption layers, including experimental methods, models and experimental data concerned with surfactants undergoing transformations in the adsorption layer.Models account both for relaxation due to surfactant diffusion and to processes internal to the adsorption layer. In particular surfactant reorientation, aggregation phase transitions and interfacial chemical reactions have been considered as possible reorganisation processes. The presented approach, allows the dilational viscoelasticity to be derived as a function of the perturbation frequency and of the equilibrium and kinetic parameters of the system. The results can also be easily specified for insoluble monolayer.The principal experimental techniques are reviewed and the recent progresses in the implementation of an Oscillation Bubble/Drop method for Capillary Pressure Tensiometer are discussed in detail.Two experimental studies of surfactants characterised by re-orientation and aggregation phase transition are presented. Beside providing a wider comprehension of these mechanisms, the interpretation of the dilational visco-elasticity data, according to the developed models, allows the effective estimation of the equilibrium and kinetic parameters.
Keywords: Soluble surfactants; Dilational visco-elasticity; Surface rheology; Liquid interfaces; Oscillating bubble; Capillary pressure tensiometry; N-dodecanol; Poly-octyethylene glycol ethers