Electro viscous effects

Another reason Einstein s equation is inaccurate is because of the electrical double layer surrounding the particles in aqueous solution. The presence of a double layer gives an electro-viscous effect which causes (1) an extra force to be needed to move two similarly charged double layers past one another and (2) a larger effective volume of the particle, due to its double layer of immobilized solvent molecules. Von Smoluchowski [16] derived an equation for the primary 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... 

Pavlik and Sansone [81] found that the size distribution of spherical particles, in the size range 5 to 40 pm, obtained by sedimentation in double-distilled deionized water plus a wetting agent was significantly different from that obtained in O.IN KCI plus a wetting agent. Coulter Counter data agreed with the tatter data. These results were later confirmed [82]. The electro-viscous effect needs to be eliminated, for Stokes law to apply, by the addition of non-ionic sedimentation liquids. 

Waters of different electrical conductivity were employed to detect a possible effect on pressure losses. Results are presented on figure 18. It can be seen that no evidence of an electro-viscous effect was observed. As explained in the theoretical section, EDL effects were a priori negligible. 

L Zurita, F Carrique, AV Delgado, The primary electro viscous effect in silica suspensions. Ionic strength and pH effects. Colloids Surfaces 92 23-28, 1994. 

Li DQ (2001) Electro-viscous effects on pressure-driven liquid flow in microchannels. Coll Surf A 195 35-57... 

In the early stages of this simplistic stability theory, the removal of the electro-viscous effect in soluble starch sols was studied These results seemed to draw the analogy between hydrophobic and... 

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... 

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