Interfacial viscosity

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... 

Rotational dynamics of a fluorescent dye adsorbed at the interface provides useful information concerning the rigidity of the microenvironment of liquid-liquid interfaee in terms of the interfacial viscosity. The rotational relaxation time of the rhodamine B dye was studied by time-resolved total internal reflection fluorescent anisotropy. In-plane... 

Surfactant Cone. (M) In-plane rotational relaxation time (ns) Interfacial viscosity (Pas)... 

This ratio implies that slip will increase as the bulk viscosity increases relative to the interfacial viscosity, or as the liquid self-cohesiveness increases and the liquid-surface affinity decreases. 

The dependence of slip on the interaction strength of the surface and liquid was studied early on by Tolstoi [3], later revisited by Blake [12], a model that is linked to interfacial viscosity. Tolstoi modeled the surface using Frenkel s model for the bulk mobility of a liquid molecule [38],... 

Another notion regarding the interfacial viscosity is as a measure of the motion of an interfacial layer. Consider an interfacial layer, a monolayer bound to the surface with interfacial density p2 a mass per unit area, moving at a constant velocity. If the surface stops suddenly, the monolayer velocity will decay exponentially with a relaxation time r. Through a quantum mechanical derivation involving the sliptime, Krim and Widom [39] determined a relationship between the interfacial viscosity, the interfacial density, and the sliptime, of the form... 

Surface shear rheology at the oil-water interface is a sensitive probe of protein-polysaccharide interactions. In particular, there is considerable experimental evidence for a general increase in surface shear viscosity of protein adsorbed layers as a result of interfacial complexation with polysaccharides (Dickinson et al., 1998 Dickinson and Euston, 1991 Dickinson and Galazka, 1992 Semenova et al., 1999a Jourdain et al., 2009). One such example is the case of asi-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = - 334 x 10 cm /mol) the interfacial viscosity after 24 hours was found to be five times larger in the presence of pectin (i.e., values of 820 80 and 160 20 mN m 1 with and without pectin, respectively) (Semenova et al., 1999a). 

There is currently little understanding of the influence of interfacial composition and (nano)structure on the kinetics of enzymatic hydrolysis of biopolymers and lipids. However, a few preliminary studies are beginning to emerge (McClements et al., 2008 Dickinson, 2008). Thus, for example, Jourdain et al. (2009) have shown recently that, in a mixed5 sodium caseinate + dextran sulfate system, the measured interfacial viscosity increased from qs = 220 mN s m 1 without enzyme to qs = 950 mN s m 1 with trypsin present. At the same time, the interfacial elasticity was initially slightly reduced from (7S = 1.6 mN m 1 to (h = 0.7 mN m, although it later returned to close to its original value. Conversely, in the... 

The material in this chapter is organized broadly in two segments. The topics on monolayers (e.g., basic definitions, experimental techniques for measurement of surface tension and sur-face-pressure-versus-area isotherms, phase equilibria and morphology of the monolayers, formulation of equation of state, interfacial viscosity, and some standard applications of mono-layers) are presented first in Sections 7.2-7.6. This is followed by the theories and experimental aspects of adsorption (adsorption from solution and Gibbs equation for the relation between... 

Emulsions and foams are two other areas in which dynamic and equilibrium film properties play a considerable role. Emulsions are colloidal dispersions in which two immiscible liquids constitute the dispersed and continuous phases. Water is almost always one of the liquids, and amphipathic molecules are usually present as emulsifying agents, components that impart some degree of durability to the preparation. Although we have focused attention on the air-water surface in this chapter, amphipathic molecules behave similarly at oil-water interfaces as well. By their adsorption, such molecules lower the interfacial tension and increase the interfacial viscosity. Emulsifying agents may also be ionic compounds, in which case they impart a charge to the surface, which in turn establishes an ion atmosphere of counterions in the adjacent aqueous phase. These concepts affect the formation and stability of emulsions in various ways ... 

Mechanism 4 also was bom in this laboratory (1-6,24). A rise in AV could be determined by the penetration and orientation of the ions of electrolyte, H20, and their products of interaction. Such ions could be part of either the hydration shell of the lipid s molecular organization or the thick interfacial viscosity layers that are located above and/or below the mathematical line (25) of surface tension. The measurements of IR absorption and surface radioactivity (see Figures 6,7,8... 

When surfactants concentrate in an adsorbed monolayer at a surface the interfacial film may provide a stabilizing influence in thin films and foams since they can both lower interfadal tension and increase the interfacial viscosity. The latter provides a mechanical resistance to film thinning and rupture. 

Insoluble polar molecules (e.g., long chain fatty acids) exhibit an extreme kind of adsorption at liquid surfaces. That is, they can be made to concentrate in one molecular layer at the surface. These interfacial films often provide the stabilizing influence in emulsions since they can both lower interfacial tension and increase the interfacial viscosity. The latter provides a mechanical resistance to coalescence. Such systems also lend themselves to the study of size, shape, and orientation of molecules at an interface. Having an adsorbed layer lowers the surface tension (to Ysolution) by the surface pressure jt= ysoivent - y solution as already noted. 

More detailed descriptions are given in Refs. [295,408,409]. Further details on the principles, measurement and applications to dispersion stability of interfacial viscosity are reviewed by Malhotra and Wasan [408], and Miller et al. [410]. 

Unlike in three dimensions, where liquids are often considered incompressible, a surfactant monolayer can be expanded or compressed over a wide area range. Thus, the dynamic surface tension experienced during a rate-dependent surface expansion, is the result of the surface dilational viscosity, the surface shear viscosity, and elastic forces. Often, the contributions of shear and/or the dilational viscosities are neglected during stress measurements of surface expansions. Isolating interfacial viscosity effects is difficult because, since the interface is connected to the substrate on either side of it, the interfacial viscosity is coupled to the two bulk viscosities. 

Therefore, it becomes laborious to determine purely interfacial viscosities without the influence of the surroundings. 

SAE could be expected to be utilized in Enhanced Oil Recovery, because their low interfacial tension and low interfacial viscosity might be predicted. Finally, emulsion breakers for crude oil may be another interesting application of SAE. 

Surfactants also reduce the coalescence of emulsion droplets. The latter process occurs as a result of thinning and disruption of the liquid film between the droplets on their close approach. The latter causes surface fluctuations, which may increase in amplitude and the film may collapse at the thinnest part. This process is prevented by the presence of surfactants at the O/W interface, which reduce the fluctuations as a result of the Gibbs elasticity and/or interfacial viscosity. In addition, the strong repulsion between the surfactant layers (which could be electrostatic and/or steric) prevents close approach of the droplets, and this reduces any film fluctuations. In addition, surfactants may form multilayers at the O/W interface (lamellar liquid crystalline structures), and this prevents coalescence of the droplets. 

Liquid-liquid interface Interfacial tension Interfacial viscosity Emulsification Electric charge... 

Type and concentration of emulsifier. The viscosity and yield value of emulsions (chemical nature of the emulsifier. Sherman (1955c) proposed two possible reasons for this, namely interfacial viscosity and interfacial adsorption. Interfacial viscosity affects the resistance of droplets to deformation, which is reflected in the resulting emulsion viscosity. A high level of interfacial adsorption enlarges the size of the interfacial layer significantly and increases emulsion viscosity. Adsorption of emulsifier at the interface should also increase with the concentration of emulsifier. The... 

Micro emulsions can be formulated with carbon dioxide in supercritical state instead of a hydrocarbon as nonaqueous solvent. Fluorinated surfactants are commonly used to prepare such microemulsions. Water-in-carbon dioxide microemulsions can be made and the droplet size has been found to be similar to the size of the droplets of water-in-hydrocarbon micro emulsions with similar composition [21]. Such a microemulsion was used for conversion of benzyl chloride to benzyl bromide using KBr as hydrophilic nucleophile. The yield was an order of magnitude higher in the carbon dioxide microemulsion than in a conventional microemulsion at similar conditions, a fact that has been ascribed to low interfacial viscosity [22]. The big advantage with these micro emulsions is the environmental friendliness and the ease of work-up associated with carbon dioxide as solvent. 

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