Remarks on excluded-volume effects in semiflexible polymer solutions

Intramolecular excluded-volume effects in stiff chains are examined by analyzing typical data of [S-2] (the mean-square radius of gyration) and [eta] (the intrinsic viscosity) for four different polymers with Kuhn segment lengths lambda(-1) of 7.8-86 nm on the basis of the wormlike chain. The data are shown to be explained almost quantitatively in the Yamakawa Stockmayer-Shimada scheme for wormlike or helical wormlike chains, leading to the conclusion that the expansion factor versus scaled excluded-volume parameter relations established by Yamakawa, Einaga, and coworkers for [S-2] and [eta] of linear flexible polymers apply to semiflexible chains in a good approximation. For typical stiff chains, the volume effects are negligibly small up to a reduced contour length lambda L of 20-50, as was found by Norisuye and Fujita. This substantially unperturbed behavior is due to the fact that the reduced excluded-volume strength lambda B for such a chain is one order of magnitude smaller than those for flexible chains in good solvents. It is noted, however, that a stiff chain starts deviating from the unperturbed state at lambda L similar to 3 when it happens to have a lambda B value comparable to those for the latter group.