Rheology interfacial

It has long been argued that interfacial rheology, namely interfacial viscosity and elasticity, play an important role in emulsion stability. This is particularly the case with mixed surfactant films (which may also form liquid crystalline phases) and polymers such as hydrocolloids and proteins that are commonly used in food emulsions. 

A fluid interface in equilibrium exhibits eui intrinsic state of tension that is characterized by its interfacial tension y which Is given by the change In free energy with area of the interface, at constant composition nj euid temperature T, 

The unit for y is energy per unit area (mjm ) or force per unit length (mNm ) which are dimensionally equivalent. Adsorption of surfactants or polymers lowers the inter-facial tension and this produces a two dimensional surface pressure n that is given by 

The interface is considered to be a macroscopically planer, dynamic fluid interface. Thus, the interface is regarded as a two-dimensional entity independent of the surrounding three-dimensional fluid. The interface is considered to correspond to a highly viscous insoluble monolayer and the interfacial stress acting within such a monolayer is sufficiently large compared to the bulk-fluid stress acting across the interface and in this way one can define an interfacial shear viscosity qj. 

Many surface viscometers utilize torsional stress measurements upon a rotating ring, disk or knife edge (shown schematically in Fig. 5.16) within or near to the liquid/liquid interface [17]. This type of viscometer is moderately sensitive for a disk viscometer the interfacial shear viscosity can be measured in the range q 10 Surface Pas. The disk is rotated within the plane of the interface with angular velocity w. A torque is exerted upon the disk of radius R by both the surfactant film with surface viscosity qg and the viscous liquid (with bulk viscosity q) that is given by the expression 

Interfaces exist by virtue of the adjoining bulk phases in other words, interfaces are not autonomous. The interface and the bulk phases are mechanically coupled, which implies that any deformation or flow in either adjacent bulk phase induces a motion in the interface, and vice versa. 

Interfadal films show both viscosity and elastidty. Films are elastic if they resist deformation in the plane of the interface and if the surface tends to recover its natural shape where the deforming forces are removed [17]. Similar to bulk materials, interfadal elasticity can be measured by static and dynamic methods. Another important interfadal rheological parameter is the dUational elastidty, e, that is given by 

A second example in which surface rheology was applied to investigate emulsion stability is the work of Biswas and Haydon [19]. These authors systematically investigated the rheological charaderistics of various proteins (which are relevant to food emulsions), namely albumin, poly( -L-lysine) and arabinic acid at the O/W interface, and correlated these measurements with the stability of the oil droplets at a planar O/W interface. 

The viscoelastic properties of the adsorbed films were studied using two-dimensional creep and stress relaxation measurements in a specially designed 

After 30 minutes, when the external force was withdrawn, the film tended to revert to its original state, with an instantaneous recovery followed by a slow one. The original state, however, was not obtained even after 20 h and the film seemed to have undergone some flow. This behaviour illustrates the viscoelastic property of the bovine serum albumin film. 

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The interfacial rheologic properties are extremely sensitive parameters toward the chemical composition of immiscible formation liquids [1053]. Therefore comparison and interpretation of the interfacial rheologic properties may contribute significantly to extension of the spectrum of the reservoir characterization, better understanding of the displacement mechanism, development of more profitable enhanced and improved oil-recovery methods, intensification of the surface technologies, optimization of the pipe line transportation, and improvement of the refinery operations [1056]. 

Interfacial rheologic properties of different crude oil-water systems were determined in wide temperature and shear rate ranges and in the presence of inorganic electrolytes, surfactants, alkaline materials, and polymers [1056]. 

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

I. Lakatos and J. Lakatos-Szabo. Effect of lOR/EOR (improved oil recovery/enhanced oil recovery) chemicals on interfacial rheological properties of crude oil/water systems. In Proceedings Volume. SPE Oilfield Chem Int Symp (Houston, TX, 2/13-2/16), 2001 SPE Number 65391. 

J. Lakatos-Szabd and I. Lakatos. Effect of sodium hydroxide on interfacial rheological properties of oil-water systems. In Colloids Surfaces, Sect A, volume 149, pages 507-513. 9th Surface Colloid Sci Int Conf (Sofia, Bulgaria, 7/6-7/12), 1997. 

J. Lakatos-Szabo, I. Lakatos, and B. Kosztin. Role of interfacial rheological properties of oil/water systems in mechanism and design of EOR/IOR technologies. In Proceedings Volume, number 057. 9th EAGE Impr Oil Recovery Europe Symp (The Hague, Netherlands, 10/20-10/22) Proc, 1997. 

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... 

Bos, M.A., van Vliet, T. (2001). Interfacial rheological properties of adsorbed protein layers and surfactants. Advances in Colloid and Interface Science, 91, 437-471. 

Murray, B.S. (2002). Interfacial rheology of food emulsifiers and proteins. Current Opinion in Colloid and Interface Science, 7, 426 131. 

Murray, B.S., Dickinson, E. (1996). Interfacial rheology and the dynamic properties of adsorbed films of food proteins and surfactants. Food Science and Technology International (Japan), 2, 131-145. 

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... 

We can distinguish between two types of stresses on an interface a shear stress and a dilatational stress. In a shear stress experiment, the interfacial area is kept constant and a shear is imposed on the interface. The resistance is characterized by a shear viscosity, similar to the Newtonian viscosity of fluids. In a dilatational stress experiment, an interface is expanded (dilated) without shear. This resistance is characterized by a dilatational viscosity. In an actual dynamic situation, the total stress is a sum of these stresses, and both these viscosities represent the total flow resistance afforded by the interface to an applied stress. There are a number of instruments to study interfacial rheology and most of them are described in Ref. [1]. The most recent instrumentation is the controlled drop tensiometer. 

Broadly speaking, the mechanical properties can be divided into two classes bulk and interfacial . Within the bulk properties are included the shear and extensional viscosities, moduli and yield stresses (material constants that relate stress to strain or strain rate), and within interfacial rheology are included the wall-slip and friction effects. The interfacial properties are independent of bulk mechanical properties and governed by the frictional or surface forces which are thought to operate at relatively... 

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... 

Anseth, J.W., Bialek, A., Hill, R.M. and Fuller, G.G. (2003) Interfacial rheology of graft-type polymeric siloxane surfactants. Langmuir, 19(16), 6349-56. 

C. N. R. Interfacial Rheology of an Ultrathin Nanocrystalline Film Formed at the Liquid/Liquid Interface. Langmuir 2007,23,3084-3087. 

The measurement of rheological properties at the surface of a solution or the interface between a solution and, for example, a biological film is called surface or interfacial rheology. In this technique also, experiments are performed either in tension, compression or shear, and phenomena observed in bulk rheology such as flow and viscoelasticity are also observable. An introduction to the techniques available and some key findings are discussed by Warburton. ... 

Warburton, B. Interfacial rheology. Curr. Opin. Colloid Interf. Sci. 1996, 1, 481 86. 

To be systematic, we shall treat static measurements first, followed by dynamic ones in sec. 1.14. Interfacial rheology will be considered In chapters 3 and 4. 

Typically dynamic techniques (overflowing weirs, cylinders, capillary waves, etc,) will be discussed in sec. 3.7 on Interfacial rheology. 

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