Viscosity measurement represents one of the simplest experimental techniques for characterizing polymers. In general, the viscosity of a polymer solution depends on the molecular weight of the polymer and on the configuration of the molecules. For essentially linear polymers such as the polyacrylamide flocculants, coiling of the molecule in response to changes in its environment leads to changes in viscosity which can be evaluated in terms of an effective radius of gyration.
For flexible molecules which form random coils in solution it can be shown that the radius of gyration (Rg), defined as the root-mean-square distance of the elements of the chain from its center of gravity, can be calculated from viscosity data using the following relation:
[n] = 14.7∅Rg/M………………………………………………(1)
where M is the molecular weight of the polymer, ∅ is Flory’s universal constant (2.1×10)21) and [n] is the intrinsic viscosity of the solution defined by:
in which n is the viscosity of a polymer solution of concentration C and η0 is the viscosity of the pure solvent.
It should be emphasized that the application of Equation 1 to aqueous solutions of polymer flocculants is approximate at best since it is by no means clear that ….Read more