Dynamic light scattering and dynamic viscoelasticity of poly (vinyl alcohol) in aqueous borax solutions. 4. Further investigation on polymer concentration and molecular weight dependencies

Viscosity measurements are made on aqueous borax solutions of poly(vinyl alcohol) (PVA) samples over a wide range of PVA concentration, C, to examine the hydrodynamic properties of associated polymers compared to those of neutral polymers. The dynamic viscoelastic data are reanalyzed using a statistical-mechanical theory for elastically effective chains in transient gels developed by Tanaka and Ishida. The viscosity data are not superposed in the plot of viscosity against C[η] using the Huggins relationship, especially around and over a critical concentration, C_N, at which the dynamical behaviors drastically change and an inflection point of a curve in the plot of the viscosity against C is located. On the other hand, when we assume that the chain dimension around C_N is the unperturbed one, the viscosity data around C_N is well-superposed on a curve in the plot of viscosity against C/C*_up, where C*_up is the overlapping concentration of the unperturbed chain. The inflection point of this composite curve is located at C/C*_up = 1, which infers that CN corresponds to the overlapping concentration. All data of the density of elastically effective chains, ν_eff, are superposed on a curve in the plot of νe_fflν against (C - C_N)/C_N where ν is the density of polymer chains, which implies that C_N should be regarded as a kind of gel point. Some discrepancies between the experimental data and the theoretical curve were observed, some of which cannot be explained using the pairwise association of PVA chains.