Shear repulsion number

A second dimensionless group is termed the shear-repulsion number, defined as the measure of convective force to electrostatic repulsive force... 

The methodology discussed previously can be applied to the study of colloidal suspensions where a number of different molecular forces and hydrodynamic effects come into play to determine the dynamics. As an illustration, we briefly describe one example of an MPC simulation of a colloidal suspension of claylike particles where comparisons between simulation and experiment have been made [42, 60]. Experiments were carried out on a suspension of AI2O3 particles. For this system electrostatic repulsive and van der Waals attractive forces are important, as are lubrication and contact forces. All of these forces were included in the simulations. A mapping of the MPC simulation parameters onto the space and time scales of the real system is given in Hecht et al. [42], The calculations were carried out with an imposed shear field. 

The number of forces separating the particles is smaller. Repulsive forces act between particles with the same electrostatic charge. The mixing of fiuids leads to the development of shear forces, which try to separate the particles. The maximum hydrodynamic force acting on spheres in a uniform shear field can be expressed as [22,24] ... 

The effect of sodium hydroxide on the low-shear viscosity can be explained as follows HPAM undergoes further hydrolysis in the presence of strong alkalis (base hydrolysis). As the polymer is hydrolyzed, the number of the carboxylate groups (i.e., the number of negative charges) on the polymer chain increases. Consequently, the electrostatic repulsion increases, and the chain size increases. This increase in the polymer chain size enhances the viscosity of the polymer solution in deionized... 

The zeta potential is the potential at the surface between a stationary solution and a moving charged colloid particle. This surface defines the plane of shear. Its definition is somewhat imprecise because the moving charged particle will have a certain number of counterions attached to it (for example ions in the Stern layer, plus some bound solvent molecules), the combined flowing object being termed the electrokinetic unit. The stability of colloidal suspensions is often interpreted in terms of the zeta potential, because, as we shall see, it is more readily accessible than the surface potential (Eq. 3.7), which describes the repulsive interaction between electric double layers. 

Summarizing the theoretical approaches and experimental studies, we may state that the exact nature of the shear-induced state and the complicated mechanisms involved are not yet completely understood. One important problem, which is still unsolved, concerns the role of electrostatic interactions. Many experiments show that SIS mainly occtus in the regime of very low ionic strengths, where repulsive forces are pre-dominant. Addition of salt shordd lead to enhanced collision frequency between the micellar particles, and this phenomenon should favor SIS. This assmnption is, however, in contrast to experimental observations, where shear-induced structures usually disappear upon addition of salt. Besides the large number of new results, some phenomena of SIS still remain mysterious. It is interesting... 

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