DYNAMIC LIGHT-SCATTERING EXPERIMENTS WITH AQUEOUS-SOLUTIONS OF POLYELECTROLYTES WITH HYDROPHOBIC SIDE-CHAINS IN THE PRESENCE OF SALT

Dynamic light scattering experiments are carried out with aqueous solutions of poly (4-vinylpyridine) completely quarternized with dodecyl bromide and ethyl bromide in varying ratios in the presence of salt (KBr; alpha(d) + alpha(e) = 1; 0.010 less than or equal to alpha(d) less than or equal to 0.192; alpha(d) is the degree of quarternization by dodecyl bromide and alpha(e) that with ethyl bromide). Apparent diffusion coefficients D-app (alpha(d), ($) over bar c(p)) are calculated from the data (($) over bar c(p) is the polymer concentration expressed in g dm(-3)). They are plotted as function of the reduced concentration variable lambda = (c(p)*/c(s)) as well as of the degree of quarternization by dodecyl bromide ad at constant values of lambda (c(p)* is the molar volume concentration of the repeating unit forming the polymer backbone; c(s) is the molar volume concentration of the added salt). The resulting curves indicate a characteristic change of the diffusive properties of the systems: For lambda much less than 1 one apparent diffusion coefficient is observed whereas for lambda much greater than 1 a fast and a slow diffusive mode are detected. At a constant value of lambda (lambda approximate to=2.0) the appearance of a slow diffusive mode is induced by decreasing systematically alpha(d) (alpha(d) less than or equal to 0.192; alpha(d) + alpha(e) approximate to 1). It is predicted that the location of the ''transition'' on the lambda-axis is a function of alpha(d).