Shear deformation larger particles

The larger macromolecules can be separated using larger particle size columns. However, the flow rate should be watched carefully. As the effective hydrodynamic size of the macromolecules may be reduced due to the deformation by shear (23). Figure 22.8 shows that the effective hydrodynamic size of a 12-15 X 10 MW polyacrylamide sample will not reach its maximum, or the size without shear, unless the flow rate is reduced to 0.01 ml/min. A... 

From this it is concluded that shear deformation is enhanced by the presence of relatively small particles whereas crazing is favored by larger particles. 

In any case, the existence of highly dispersed short crazes in association with rubber particles can divert, branch, or slow down a crack that could otherwise become catastrophic. The minimum effective particle size, to be sure, depends on the polymer system the greater the tendency to undergo shear deformation rather than crazing, the smaller the minimum particle size required, at least for ABS and HiPS (Bucknall and Drinkwater, 1973). Presumably effective termination of crazes and cracks requires a larger rubber particle if shear bands are not available to serve as crack stoppers. 

It is believed that a bimodal, or a broad distribution of rubber particles resulting from such rubber mixtures, helps in the craze or crack blunting because the larger particles and the small particles provide resistance to crack initiation through increased local shear deformation of the matrix. 

Small bubbles usually <100 pm diameter are found to be most effective in intercepting the su ended particles. For most applications some pretreatment with coagulating chemicals or flocculating agents is necessary to produce a floe vsbich will readily adhere to the bubbles. For aqueous sui ensions conventional water treatment chemicals are used preferably to give a small strong floe which is more likely to survive the shear forces in the liquid around the bubbles rather than larger deformable floes. 

LCP/PP 30/70 Hydrophobic nanosilica PP phase Morphology revealed deformation of LCP particles in the presence of nanosilica due to increase in the matrix viscosity and higher shear rates, resulting in a larger aspect ratio of the LCP particles Lee et al. 2006b... 

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