DYNAMIC LIGHT-SCATTERING EXPERIMENTS WITH AQUEOUS-SOLUTIONS OF POLYELECTROLYTES OF LOW CHARGE-DENSITY ALONG THE POLYMER-CHAIN IN THE PRESENCE OF SALT

Dynamic light scattering experiments are carried out with aqueous solu tions of poly(2-vinylpyridine) quaternized to small extents with ethyl bromide and dissolved in an aqueous solution of KBr (molar mass, M(w) = 3.14 . 10(5) g mol(-1); M(w)/M(n) = 2.24; degree of quaternization, alpha(e); 0.079 less than or equal to alpha(e) less than or equal to 0.461; electrolyte concentration, c(s) = 1 . 10(-2) c(+), c(+) = 1 mol dm(-3)). Apparent diffusion coefficients D-app (alpha(e), ($) over ba r c(p)) are calculated from the data (($) over bar(p), polymer concent ration (g dm(-3))). They are plotted as a function of the reduced comp osition variable Lambda = alpha(e) c(p)/c(s) (c(p)*, molar volume con centration of the repeat unit of the polymer backbone). For Lambda muc h less than 1 one apparent diffusion coefficient is observed. In the r ange Lambda approximate to 1 the value of the apparent diffusion coeff icient increases with increasing values of (alpha(e) c(p)) and a slow diffusive mode gradually appears. For Lambda much greater than 1 a fa st and a slow diffusive process is found. In the literature such a beh aviour has been reported for solutions of highly charged polyelectroly tes.