Foams interfacial rheology

The role of various surfactant association structures such as micelles and lyotropic liquid crystals (372), adsorption-desorption kinetics at liquid-gas interfaces (373) and interfacial rheology (373) and capillary pressure (374) on foam lamellae stability has been studied. Microvisual studies in model porous media indicate... 

Interfacial rheology deals with the flow behavior in the interfacial region between two immiscible fluid phases (gas-liquid as in foams, and liquid-liquid as in emulsions). The flow is considerably modified by surface active agents present in the system. Surface active agents (surfactants) are molecules with an affinity for the interface and accumulate there forming a packed structure. This results in a variation in physical and chemical properties in a thin interfacial region with a thickness of the order of a few molecular diameters. These... 

Malhotra, A.K. Wasan, D.T. Interfacial Rheological Properties of Adsorbed Surfactant Films with Applications to Emulsion and Foam Stability in Thin Liquid Films, Ivanov, I.B. (Ed.), Dekker New York, 1988, pp. 829-890. 

It can be considered from the scheme that one has to distinguish between the foam kinetics, i.e. the rate of generation of foam under well defined conditions (air input and mechanical treatment) and the stability and lifetime of a foam once generated. The foam kinetics is also sometimes termed foamability in the literature. These quantities can be related to interfacial parameters such as dynamic surface tension, i.e. the non-equilibrium surface tension of a newly generated surface, interfacial rheology, dynamic surface elasticity and interfacial potential. In the case of the presence of oily droplets (e.g. an antifoam, a... 

Interfacial rheology is a very important tool in understanding the formation, stability and other properties of emulsions and foams. It also contributes to the characterization of monolayers, in addition to spectroscopic, electric and other methods. Hence, there is a clear motive for considering it in some detail. 

Murray, B.S. Interfacial rheology of mixed food protein and surfactant adsorption layers with respect to emulsion and foam stability. Proteins at Liquid Interfaces, D. Mobius and R. Miller, eds., Elsevier, Amsterdam, 1998. 

Edwards, D.A. and Wasan, D.T., Foam rheology the theory and role of interfacial rheological properties, in Foams Theory, Measurements, and Applications, Prud home, R.K. and Khan, S.A., Eds., Marcel Dekker, New York, 1996, p. 189. 

Malhotra AK, Wasan DT. Interfacial rheological properties of adsorbed surfactant films with applications to emulsion and foam stability. In Ivanov IB, ed. Thin Liquid Films, Fundamentals and Applications. Vol. 29. Surfactant Science Series. New York Marcel Dekker, 1988 829-890. 

Dynamic properties of interfaces have attracted attention for many years because they help in understanding the behaviour of polymer, surfactant or mixed adsorption layers.6 In particular, interfacial rheology (dilational properties) is crucial for many technological processes (emulsions, flotation, foaming, etc).1 The present work deals with the adsorption of MeC at the air-water interface. Because of its amphiphilic character MeC is able to adsorb at the liquid interface thus lowering the surface tension. Our aim is to quantify how surface active this polymer is, and to determine the rheological properties of the layer. A qualitative and quantitative evaluation of the adsorption process and the dilata-tional surface properties have been realised by dynamic interface tension measurements using a drop tensiometer and an axisymmetric drop shape analysis. 

Both bulk and interfacial rheological measurements and foaming properties show a large effect of pH on these properties of glycinin dispersions. This is undoubtedly related to the change in conformation of the glycinin molecule with pH as expressed in the presence of different amounts of the 3S, 7S and 11S form at different pH.11-13... 

An actual overview on interfacial rheological properties of adsorbed surfactant layers stabilising foams and emulsions has been given by Malhotra Wasan (1988). The results of... 

Wasan and his research group focused on the field of interfacial rheology during the past three decades [15]. They developed novel instruments, such as oscillatory deep-channel interfacial viscometer [20,21,28] and biconical bob oscillatory interfacial rheometer [29] for interfacial shear measurement and the maximum bubble-pressure method [15,29,30] and the controlled drop tensiometer [1,31] for interfacial dilatational measurement, to resolve complex interfacial flow behavior in dynamic stress conditions [1,15,27,32-35]. Their research has clearly demonstrated the importance of interfacial rheology in the coalescence process of emulsions and foams. In connection with the maximum bubble-pressure method, it has been used in the BLM system to access the properties of lipid bilayers formed from a variety of surfactants [17,28,36]. 

It was discussed quite extensively, that interfacial dynamics and rheology are key properties of liquid disperse systems, such as foams and emulsions. The stability of such systems depends for example on the dilational elasticity and viscosity, however, surely not on the elasticity modulus (Borwankar et al. 1992). Here, the interfacial rheology with its frequency dependence comes into play, and data at respective frequencies will possibly correlate with the stability behaviour. 

As indicated above, emulsions and foams are thermodynamically unstable dispersions. They are distinguished from the dispersions discussed in Chapter 16 in that their dispersed phase is fluid and not solid. This has a number of consequences of which the most important ones are (1) the particles are deformable, (2) the interface between the dispersed and the continuous phases is deformable, which may give rise to interfacial rheological phenomena, and (3) the particles may coalesce. These... 

In the foregoing sections, we have seen that adsorption dynamics, that is, the rate by which the interfacial tension decreases upon adsorption of the emulsifying or foaming agent, as well as the interfacial rheological properties play key roles in the formation and subsequent long-term stability of emulsions and foams. The coarseness and the stability of these dispersions may therefore be modulated on the basis of adsorption dynamics and interfacial rheological properties. 

In Chapter 17, we discuss rheological properties, in particular viscosity and elasticity, of colloidal systems. These properties are at the basis of quality characteristics such as strength, pliancy, fluidity, texture, and other mechanical properties of various materials and products. In addition to bulk rheology, rheological features of interfaces are discussed. Interfacial rheological behavior is crucial for the existence of deformable dispersed particles in emulsions and foams. Emulsions and foams, notably their formation and stabilization, are considered in more detail in Chapter 18. 

INTERFACIAL RHEOLOGY OF HEN EGG WHITE LYSOZYME-5-METHYLRESORCINOL MIXTURES AND THEIR FOAMING PROPERTIES... 

Adsorbed protein molecules interact at the interfaces to form viscoelastic films. The viscoelastic properties of protein films adsorbed at fluid interfaces in food emulsions and foams are important in relation to the stability of such systems with respect to film rupture and coalescence. Interfacial rheology techniques are very sensitive methods to measure the viscoelastic properties of proteins, thereby evaluating the protein-protein or protein-surfactant interactions at the interfaces. There was an excellent review about the principal and methods of interfacial rheology [17]. 

The interfacial rheology of protein adsorption layers has been intensively studied in relation to the properties of foams and emulsions stabilized by proteins and their mixtures with lipids or surfactants. Detailed information on the investigated systems, experimental techniques, and theoretical models can be found in Refs. [762-769]. The shear rheology of the adsorption layers of many proteins follows the viscoelastic thixotropic model [770-772], in which the surface shear elasticity and viscosity depend on the surface shear rate. The surface rheology of saponin adsorption layers has been investigated in Ref. [773]. 

Ipsen, R., Otte, J., Sharma, R., Nielsen, A., Hansen, L. G., Brram Qvist, K. (2001). Effect of limited hydrolysis on the interfacial rheology and foaming properties of p-lactoglobulin A. Colloids and Surfaces B Biointerfaces, 21, 173—178. 

Langevin, D. 2000. Influence of interfacial rheology on foam and emulsion properties. Adv. Colloid Interface Sci. 88 (1-2) 209-222. 

Maldonado-Valderrama, J., A. Martm-Rodiiguez, M. J. Galvez-Ruiz, R. Miller, D. Langevin, and M. A. Cabrerizo-Vflchez. 2008. Foams and emulsions of P-casein examined by interfacial rheology. Colloids Surf. A Physicochem. Eng. Aspects 323 (1-3) 116-122. 

In Chapters 8 and 9, it was noted that one mechanism for the stabilization of emulsions, foams, and other fluid interfaces was the presence of a viscous or elastic interfacial layer. The extraction of oil from porous rock formations with varying pore sizes requires the expansion and contraction of oil-water interfaces. The presence of a highly viscous interfacial layer could greatly inhibit such action. Because oil deposits naturally contain surface-active components that adsorb at the 0/W interface, such elastic films are commonly encountered. To counteract their effect, it is necessary to displace the elastic interfacial film with one possessing more favorable interfacial rheological properties. 

The numerous previous studies of the flow of foam in porous media and of its application for. improving the displacement of oil from such media, have almost always been conducted under ambient conditions of temperature and pressure there have been very few reports of laboratory studies under reservoir conditions. Although many interfacial properties are known to be temperature dependant, little attention has been paid to the influence of temperature upon the properties of foam. Furthermore, the rheological properties of foams, and their effectiveness for the displacement of oil are strongly dependant upon foam quality, which is in turn... 

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