Intrinsic Viscosity, Diffusion, and Sedimentation Rate of Polymers in Solution

Intrinsic viscosity, diffusion and sedimentation rate of polymers in solution is calculated by a generalization of Einstein's theory for impermeable spheres. For the coiled polymer molecule a sphere is substituted which hinders the liquid flow through its interior only to a degree depending on the average density in space of the polymer molecule in solution. The amount of shielding of the liquid flow which is introduced in this way determines the exponent in the customary exponential relation between intrinsic viscosity, diffusion, or sedimentation rate and molecular weight. This relation is shown to have only the merits of an interpolation formula. It is shown how the dimensions of the molecular coil can be derived from the experimental data on viscosity, and these dimensions are compared with those derived from interference measurements. The point is stressed that the relation between intrinsic viscosity and molecular weight is rather indirect and depends essentially on the type of polymer molecule under consideration. In most cases polymer molecules are decidedly stiffer and therefore cover a larger space in solution than would be expected from models with free rotation around bonds.