The Hofmeister Anion Effect and the Growth of Polyelectrolyte Multilayers

The influence of a variety of counteranions on the properties of polyelectrolyte multilayers deposited by layer-by-layer technique is studied by using ellipsometry and AFM. We found out that in thin dry multilayers (20−90 nm) of poly(4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA), the thickness follows reasonably well the position of the counteranion in the Hofmeister series. The polyelectrolyte−counteranion interaction is studied by means of viscosity measurements of semidilute solutions of PDADMA in the presence of different anions. The dynamic viscosities follow the Hofmeister series of anions and correlate with the thickness of multilayers. Two parameters describing the interaction of ions with water, the Jones−Dole viscosity B coefficient and the hydration entropy, are used to explain the anion effect on the developing multilayer thickness. Reasonably smooth and monotonic functional dependence is observed between the layer thickness and these two parameters.