Interfacial viscosity definition

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... 

The fluorescent molecule, CigRBH+, can be used as an alternative probe in the measurement of the interfacial viscosity of microparticles (about 0.5 mm in size) or rotating disks (several, 10 cm in radius) [29,30]. In comparison with the microparticles, the molecular probe has definite advantages. One of those is that the interference of the bulk viscosity is negligibly small and that information about the nano-environment around the probe can be obtained. 

The presence of a low-viscosity interfacial layer makes the determination of the boundary condition even more difficult because the location of a slip plane becomes blurred. Transitional layers have been discussed in the previous section, but this is an approximate picture, since it stiU requires the definition of boundary conditions between the interfacial layers. A more accurate picture, at least from a mesoscopic standpoint, would include a continuous gradient of material properties, in the form of a viscoelastic transition from the sohd surface to the purely viscous liquid. Due to limitations of time and space, models of transitional gradient layers will be left for a future article. 

A useful generalization noted in the previous section is the widespread applicability of impeller Reynolds number for correlating performance data from different-scale operations in geometrically similar systems. In some heterogeneous systems, it may be necessary to modify the definitions of density and viscosity for use in this Reynolds number, and to introduce groups like the Weber number to account for interfacial forces (see Section V). The main point is that it requires experiment to establish finally the form of the controlling groups. 

The presence of liquid crystalline phases, their intermolecular structure and especially their state of dispersion definitely can affect interfacial tensions and interfacial tension transients (10), and may also influence other factors such as viscosity and the retention of surfactant during flow through a porous medium. 

Based on the definition of the capillary number, the two-phase flow patterns in microchannels can be influenced by interfacial forces (fluid viscosity (rf), flow velocity (v), and geometric features (G). The interfacial forces can be modulated by adding surfactants, surface coating, and patterning techniques but also by electrical, thermal, or optical modulations of the interfacial... 

In Eq. 9, E is the interfacial tension, p the pressure, Vy the undisturbed velocity gradient tensor and Vy its transpose, tjm is the viscosity of the continuous phase, V is the total volume of the system, n is the unit vector orthogonal to the interface between the two phases, u is the velocity at the interface, dA is the area of an interfacial element and the integrals are evaluated over the whole interfadal area of the system, A. Since the constituents are assumed to be Newtonian all nonlinear contributions to the stress a(t) are caused entirely by the deformation of the droplet interface. The unit vectors n and u describe this deformation and can be computed using the Maffettone-Minale (MM) model for different frequencies and amplitudes. The MM model uses a second rank, symmetric and positive definite... 

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