Polymer sedimentation

In the determination of the molecular weight of the polymer, sedimentation investigations of its solutions may be replaced by viscometric measurements. It is known 3) a combination of intrinsic viscosity, [n], and diffusion coefficient, D, leads to the equation ... 

Several lines of evidence indicate that a is actually sensitive to the spatial extent of the matrix polymer, not to the matrix molecular weight. The a decreases if one moves the matrix polymer from a good to a Theta solvent. At elevated polymer concentration, three-arm star polymers sediment two or three times faster than do linear polymers of about the same molecular weight. Sedimentation is also slowed if the matrix chains are made more rigid - based on studies on polyelectrolyte matrices - though it is unclear whether the chain rigidity or the polymer spatial extent is the key variable. 

Actually some mustard types contain considerable amounts of by-products arising from the production process. In particular, the "direct process" for synthesis of mustard formed polysulfide by-products. If they were not separated in the course of fabrication, such polymer sediments in filled munitions become a problem during longterm storage. Also, problems may arise in the dismantling process owing to residues that obstinately stick to the walls of shells being emptied. 

Typical examples of solid samples include large particulates, such as those found in ores smaller particulates, such as soils and sediments tablets, pellets, and capsules used in dispensing pharmaceutical products and animal feeds sheet materials, such as polymers and rolled metals and tissue samples from biological specimens. 

At first glance, the contents of Chap. 9 read like a catchall for unrelated topics. In it we examine the intrinsic viscosity of polymer solutions, the diffusion coefficient, the sedimentation coefficient, sedimentation equilibrium, and gel permeation chromatography. While all of these techniques can be related in one way or another to the molecular weight of the polymer, the more fundamental unifying principle which connects these topics is their common dependence on the spatial extension of the molecules. The radius of gyration is the parameter of interest in this context, and the intrinsic viscosity in particular can be interpreted to give a value for this important quantity. The experimental techniques discussed in Chap. 9 have been used extensively in the study of biopolymers. 

This chapter contains one of the more diverse assortments of topics of any chapter in the volume. In it we discuss the viscosity of polymer solutions, especially the intrinsic viscosity the diffusion and sedimentation behavior of polymers, including the equilibrium between the two and the analysis of polymers by gel permeation chromatography (GPC). At first glance these seem to be rather unrelated topics, but features they all share are a dependence on the spatial extension of the molecules in solution and applicability to molecular weight determination. 

We shall see in Sec. 9.10 that sedimentation and diffusion data yield experimental friction factors which may also be described-by the ratio of the experimental f to fQ, the friction factor of a sphere of the same mass-as contours in solvation-ellipticity plots. The two different kinds of contours differ in detailed shape, as illustrated in Fig. 9.4b, so the location at which they cross provides the desired characterization. For the hypothetical system shown in Fig. 9.4b, the axial ratio is about 2.5 and the protein is hydrated to the extent of about 1.0 g water (g polymer)". ... 

Mandelkern and Floryt have assembled the sedimentation coefficients and intrinsic viscosities for polymers of various molecular weights. As shown... 

Protein molecules extracted from Escherichia coli ribosomes were examined by viscosity, sedimentation, and diffusion experiments for characterization with respect to molecular weight, hydration, and ellipticity. These dataf are examined in this and the following problem. Use Fig. 9.4a to estimate the axial ratio of the molecules, assuming a solvation of 0.26 g water (g protein)"V At 20°C, [r ] = 27.7 cm g" and P2 = 1.36 for aqueous solutions of this polymer. 

Additionally, mechanical (primarily shear), freeze—thaw, and thermal stabiHty the tendency to form sediment on long-term standing and compatibiHty with other dispersions, salts, surfactants, and pigments of acryHc dispersions are often evaluated. Details on the determination of the properties of emulsion polymers are available (60). 

In the absence of ammonia and the concentration of polyamines being > 20 p.M the production of sediments take place. Ethylene diamine reacts with Hg(II) in the form of diimide -HNRNH- to form the insoluble complex IHgHNRNHHgl. In the presence of ammonia the production of sediments having complex composition is also possible. Given concentration of K Hgl 1-2 mM, NaOH 60-120 mM and compai able amounts of ammonia and ethylene diamine the products of reactions ai e only the soluble green-coloured complexes, bearing ammonia in the form of nitride and ethylene diamine in the form of diimide. Those complexes ai e polymers, with their absorption spectmms being different from those of the similar polymeric ammonia complexes. 

The hydrodynamic radius reflects the effect of coil size on polymer transport properties and can be determined from the sedimentation or diffusion coefficients at infinite dilution from the relation Rh = kBT/6itri5D (D = translational diffusion coefficient extrapolated to zero concentration, kB = Boltzmann constant, T = absolute temperature and r s = solvent viscosity). 

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