Mechanical losses shear stability mechanisms

He have presented a simple procedure whereby one can estimate the stability of a colloidal system undergoing simultaneous creaming and gravity-induced flocculation. This procedure is by no means restricted to only this case. One can easily take into account other particle loss mechanisms, such as shear-induced flocculation or Brownian flocculation. What is required in these cases are the appropriate particle/particle collision kernels, which can be computed by solving the governing convective-diffusion equation. 

The attributes of a SEC column packing material are listed in Table 2. As indicated, the support must be optimized with respect to specific resolution, efficiency, column pressure, and mechanical, chemical, and thermal stability. Recovery of mass and activity is particularly important in the analysis and purification of biopolymers. It also plays a role in the analysis of nonbiochemical synthetic polymers on silica-based SEC columns. In addition to recovery losses by adsorption, the recovery for both groups of polymers can also be reduced by polymer degradation as a result of, for instance, mechanical shear. 

The mechanism of the formation of such stripes can be the following. Under plastic deformation the material can reach some definite limit of hardening (here this problem is not discussed in detail). Then this material behaves as an ideally plastic material. From the theory of ideal plasticity, it is known that such a state is the necessary condition for the loss of the stability of homogeneous plastic flow, that is, layers of large plastic shear appear. Such layers are modeled as the surfaces of the shear. That is to say, the parts of the material separated by these surfaces slip relative to each other with a resistance to the plastic flow that is equal to the plastic shear stress for this material. The disposition of the shear surface for die-forming is shown in Fig. 20. 

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