Detailed static and dynamic light-scattering experiments were performed on salt-free solutions of sodium poly(styrene sulfonate) with 13 different molecular weights ranging from Mw=5000 to 1 200 000 at moderate concentrations in the interval c=10 – 45.6 g/L. Two diffusion coefficients, Df (fast) and Ds (slow), were characterized as is typical for such a system. The fast-diffusive mode, corresponding to the coupled diffusion of polyions and counterions, is completely dominated by the counterion’s influence. Df is found to be independent of molecular weight over the broad range used in this study. On the other hand, Ds, which corresponds to the dynamics of large multichain domains in solution, is strongly dependent on molecular weight. The apparent dimensions of the domains are calculated from the angular dependencies of Ds and from the total scattered light intensity. The concentration dependence of Ds is in the form of a power law Ds∼c−ν, where the exponent ν is dependent on molecular weight in the form ν∼Mμw. This is in contrast to the isotropic model of polyelectrolyte solutions proposed by de Gennes and Odijk, which predicts that the behavior of a semidilute solution does not depend on molecular weight. It appears that interactions on a much larger scale than the correlation length of the entangled network must be taken into account.

Static and dynamic laser light scattering were used to bring evidence of large-scale supramolecular structure in solutions of low molar mass electrolytes, nonelectrolytes, and mixtures of liquids. It was shown that solutes are distributed inhomogeneously on large length scales. Regions of higher and lower solute concentration exist in solution and give sufficient scattering contrast for experimental observation. A detailed light scattering study showed that these regions can be characterized as close-to-spherical discrete domains of higher solute density in a less dense rest of solution. These domains do contain solvent inside and can be therefore characterized as loose associates (giant clusters, aggregates). Their size distributions are significantly broad, ranging up to several hundreds of nanometers. Characteristic sizes of these inhomogenities thus exceed angstrom dimensions of individual molecules by several orders of magnitude. The number of solute molecules per domain varies approximately in the range 10(3)-10(8). Phenomena described were observed in a very broad range of solutes and solvents. Among others, selected data on most common substances of great chemical and biological importance such as sodium chloride, citric acid, glucose, urea, acetic acid, and ethanol are presented.

Static and dynamic light-scattering measurements were carried out on salt-free aqueous sodium poly(styrene sulfonate) solutions. The concentration dependence of the solution behavior was investigated in the range c=0.01– 45.6 g/L for three samples with Mw=5000, 100 000, and 1 200 000. A critical concentration ccr≂0.5 g/L was experimentally established. Above ccr, two diffusion coefficients Df (fast) and Ds (slow) were measured. Df, corresponding to the coupled diffusion of polyions and counterions, is independent of concentration. Ds, corresponding to the presence of multichain domains in solution, increases upon dilution. The angular dependence of the scattering intensity as it reflects the size of domains becomes less pronounced upon dilution and, at c=ccr, the scattering intensity is independent of angle. The concentration dependence of the excess scattering intensity is stronger than linear (the reduced intensity I/c increases with concentration). Below ccr, Df decreases upon dilution and finally merges with Ds. The scattering intensity is first independent of angle, then upon dilution a broad maximum appears. The concentration dependence of the excess scattering intensity is weaker than linear (the reduced intensity I/c decreases with concentration). These experimental data indicate that, for c<ccr, repulsive Coulombic interactions screened by the presence of counterions dominate. For c>ccr, the solution structure and dynamics are predominantly influenced by coupled polyion-counterion dynamics and the presence of attractive forces giving rise to domains. The critical concentration ccr is independent of molecular weight. A concentration molecular weight regime diagram is constructed combining the present data with previous results on the molecular weight dependence and with literature data on very dilute solutions.

The ionic strength dependence of the structure and dynamics of polyelectrolyte solutions was investigated by static and dynamic light scattering. Narrow molecular weight distribution sodium poly͑styrenesulfonate͒ ͑NaPSS͒ standards in aqueous NaCl solutions were chosen as model systems. The study covers moderate polymer concentrations ͑ϳ0.5-50 g/L͒ where interparticle interactions rather than single-polyion properties are dominant. Two diffusive modes characterized as fast and slow were detected in most cases. Scattering amplitudes of these modes were evaluated from light scattering data, which was not done in previous investigations. Amplitudes were normalized by the scattering of a benzene standard. Attention was paid mainly to the occurrence of the slow diffusive mode, which is interpreted as the dynamics of large multichain domains. Experimental results show that the occurrence of the slow mode is not connected with any kind of a sharp transition at some critical conditions. The amplitude of the slow mode ͑scattering intensity associated with the slow mode͒ changes smoothly as a function of the ratio of the polymer concentration to the solution ionic strength. At sufficiently high polymer concentrations, the slow mode can even persist until theta conditions are reached ͑4.17 M NaCl at 25°C͒. It was shown that the absolute scattering intensity associated with the slow mode increases upon decreasing ionic strength, which is a direct proof that the structures responsible for the slow mode ͑domains͒ really form in solution and cannot be associated with the presence of some impurities, stable aggregates due to the polymer incomplete solubility, etc. Multiangle dynamic light scattering data show that dimensions of the domains increase upon decreasing ionic strength, too. The fast and slow diffusive modes are always widely separated on the time scale and the ionic strength dependence of diffusion coefficient cannot be characterized as a ''splitting of diffusion coefficient.''