Hydrodynamic Properties of Short NaPMA in Excess Salt: a Dynamic Light Scattering Study

Diffusion of short poly(methacrylic acid) (Na-PMA, M = 6600 g/mol) in aqueous solution has been investigated by means of dynamic light scattering at different scattering angles, ionic strengths, pH, and polymer concentrations in the pH range between 2.1 and 8.2. At pH = 2.14, only one fast relaxation mode was observed whereas at higher pH-values a fast and a slow mode could be determined. Whereas the slow mode is due to collective diffusion of polyelectrolyte domains, the fast mode at a sufficiently high ionic strength (I > 0.1 mol/L) is caused by the diffusion of single polyelectrolyte chains. From the dependence on the polymer concentration, self-diffusion coefficients at infinite dilution, the corresponding hydrodynamic radii, and second virial coefficients were determined and discussed. It was concluded that PMA exists as a random coil in excess electrolyte solution in the whole pH range, although a slight stretching was observed for pH > 4