Chain contraction at the critical overlap concentration

The sedimentation of dissolved macromolecules is analyzed in both the regions of very dilute solution and in semidilute regime employing the fractal aggregate model of macromolecular coils and blobs. The macromolecules entering the overlapping region are represented by more compact aggregates than that modeling the individual macromolecule of the same mass and fractal dimension. This regularity is confirmed by analyzing the hydrodynamic behavior of several polymer-solvent systems in a wide interval of fractal dimension including the polymers dissolved in both the theta and real solvents. The reduced hydrodynamic volume of macromolecules is about 0.3-0.5 of that of the individual macromolecule. This well corresponds with the literature data obtained by measurement of the reduction of the static correlation length with concentration and those determined by dielectric study of the end-to-end distance.