Viscosity electro-viscous effect

If the liquid contains an electrolyte and the particles are charged, then the effective viscosity is further increased. This phenomenon is called the primary electro-viscous effect [3-18] and the effective viscosity can be expressed as... 

Even dilute suspensions of repulsive particles will have slightly greater viscosity than hard spheres because of the additional viscous dissipation related to the flow of fluid through the repulsive region around the particle. For particles with EDL repulsion this is known as the primary electro-viscous effect (Hunter, 2001). The total drag on the particle and the double layer is greater than the drag on a hard sphere. The increase in viscosity due to the primary electro-viscous effect is typically minimal. 

Concentrated suspensions can have significantly elevated viscosities (relative to hard spheres at the same volume fraction) due to the interaction between overlapping EDLs. For particles to push past each other the double layer must be distorted. This effect is known as the secondary electro-viscous effect (Hunter, 2001). Similar effects occur when the repulsion is by steric mechanism. 

Electro-viscous Effects. The first electro-viscous effect This is an increase of the viscosity due to an increase of energy dissipation caused by the distortion of the double layer under shear conditions. 

The second electro-viscous effect. In concentrated emulsions, the double layers may interact or even overlap, and the mutual repulsion may cause an increase in viscosity. This effect is proportional to and inversely proportional to the ionic strength. Because of the interactions between the double layers and the entrapment of part of the continuous phase in floes, a viscosity minimum at a specific electrolyte concentration can be observed. It occurs when the flocculation of the emulsion leads to a network. 

In spite of these ambiguities, it is clear from the following estimation that the effect of ionic atmosphere can cause a change in q Pq First, we shall assume that the electro viscous effect disappears at infinite dilution of the macro-ion, and that the magnitude of the intrinsic viscosity is little influenced by flow perturbations originating from the ionic atmosphere. These assumptions are supported by the experimental observations that (a) The intrinsic viscosity of globular proteins are independent of the charges on their surface [20] and (b) that the intrinsic viscosities of linear polyions are at least qualitatively accounted for by theories which take into account only the... 

In HEC-thickened formulations, low-shear-rate viscosities increase with decreasing latex particle size. This effect has been a major limitation in formulating small-particle latices. The phenomenon appears to arise from electro viscous, hydration, or flocculation effects, not a depletion layer mechanism. Associative thickeners achieve efficient viscosity in coating formulations via participation in synthesis and formulation surfactant micelles to form pseudo macromolecules and via an ion-dipole interaction between the cations of surface carboxylate groups on the latex and the ether linkages of the associative thickener. Generally, an excess of synthesis surfactant is found in the production of small-particle latices. The achievement of lower viscosities in small-particle ( 100 nm) latex coatings thickened with associative thickener appears to occur by extensive disruption of the polymer hydrophobe s participation in intermicellar networks. 

The optical microscopy or TOA of the smectic side-chain polymers shows the important effect that viscosity has on the behaviour of these systems, i.e. the existence of T and the fluid region, the rate of growth of texture on cooling and the immobility of the texture below r. Since smectic materials will be more viscous than the nematic phases, this suggests again that the materials should be useful for the storage of electro-optic information if this information can be written on an acceptable timescale. 

In order to do this, the viscous pressure drop APq of Fig. 6.66 is deducted from the total pressure drop APeo to give the electro or yield pressure APg for a particular voltage. Given the valve dimensions and using the dynamic viscosity as calculated from the zero-volts line and the valve dimensions, the yield stress at the wall may be isolated and 7 calculated. Likewise, shear stress T and y(= ujR/h) can be calculated from the shear mode test data -by neglecting radial effects. The well known relevant Poiseuille and Couette flow analysis are often used in these procedures. In both modes /r is derived from the zero-volts test. On this basis, flow- and shear- mode data will not necessarily correspond in the t, 7-plane. 

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