The effect of ionic strength on electrical properties of polyelectrolyte multilayers on colloidal particles

The effect of ionic strength on the electrical properties of poly(styrene sulfonate)/poly(allylamine) (PSS/PAH) multilayer film was investigated using electric light scattering and electrophoresis. A multilayer film was created by sequential adsorption of fully charged polymers from solutions containing 10 (- 1) M NaCl and its properties were compared to those of a PSS/PAH film prepared in the absence of salt. All measurements were carried out after rinsing the films with an aqueous solution of HCl to adjust the pH to 4.6. We found that the electrical polarizability of the film coated particles and its frequency of relaxation increase when the film was constructed in the presence of salt. The increase in the electrical polarizability value is due to the screening-enhanced adsorption. We hypothesize that the increase in the relaxation frequency of the electrical polarizability is a consequence of the adsorption of the polymer chains in more coiled conformations. This restricts the movement of small ions to shorter distances than in the film prepared without salt. In both cases, the small ions are located near the film surface, which indicates the key role of the last deposited polymer for the behavior of the entire PSS/PAH film.