Long rods

Some polymers are naturally rod-Uke, for instance xanthan gum Mw 2 x 1(P, with a typical length up to 1 micron and an aspect ratio, l/d, of 600), while others can become rod-like. An example of the latter is a polyelectrolyte in a very low electrolyte solution, where the electrostatic charges along the polymer chains repel each other and force the convoluted chain to become straight. For rod-Uke polymers with an aspect ratio of up to around 200, the relative increase in viscosity compared with the solvent rjsp = (tj- r]s)/tis) is given by the approximate relationship [1] 

The extensional viscosity (see chapter 17 for details) of semi-dilute suspensions of long rod- or fibre-Uke entities (xanthan gum being a good example) is given by [2] 

This shows that the aspect ratio plays a dominant part in determining the extensional viscosity. 

Melts and concentrated solutions are elastic because tension in the chains between entanglements persists while the entangled chains slide over each other. The transient networks present in such situations are elastic on a short time-scale, but as the stretched chains slide over each other and loose entanglements, they relax and show normal viscous behaviour. 

All the individual curves for a series of molecular weights, temperatures and shear rates can often be incorporated into a single master curve by plotting the non- 

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These assemblies are made of a spider on which 2,5 to 4 m long rods are welded. These rods (16 to 24 per assembly) contain neutron-absorbing material. The rod envelope is made of 0,5 to 1 mm thick steel. The rod diameter is approximately 10 mm. 

Impact resistance is determined usiag flyer plate impact tests, long rod impact tests, Hopkinson bar tests (50), and the Hquid jet technique (51). Impact damage resistance is often quantified by measuring the postimpact strength of the ceramic. 

Figure 14.1 Each polypeptide chain in the collagen molecule folds into an extended polyproline type II helix with a rise per turn along the helix of 9.6 A comprising 3.3 residues. In the collagen molecule three such chains are supercoiled about a common axis to form a 3000-A-long rod-like molecule. The amino acid sequence contains repeats of -Gly-X-Y- where X is often proline and Y is often hydroxyproline. (a) Ball and stick model of two turns of one polypeptide chain.

Colloidal suspensions are, per definition, mixtures of mesoscopic particles and atomic liquids. What happens if there are several different species of particles mixed in the solvent One can invent several different sorts of mixtures small and large particles, differently charged ones, short and long rods, spheres and rods, and many more. Let us look into the literature. One important question when dealing with systems with several components is whether the species can be mixed or whether there exists a miscibility gap where the components macroscopically phase-separate. 

Figure 9.87. Heat flow in rod with heat loss to surroundings (a) A long rod with temperature falling to that of surroundings, that is 9 — 0 when x = oc.

The long rod-like shape of collagen provides rigidity and strength to support the architecture of organs and tissues and to make connective tissue. 

The explosive may also be extruded in the form of a long rod which is then cut into pieces of the required length on a table covered with a copper or brass sheet. The pieces are then put into paper cartridge cases which should be made of paraffined paper. 

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