Salt-induced changes in the growth of polyelectrolyte layers of poly(diallyl-dimethylammonium chloride) and poly(4-styrene sulfonate of sodium)

Multilayers formed by the sodium salt of poly(4-styrene sulfonate), PSS, and poly(diallyldimethylammonium) chloride, PDADMAC, have been built by electrostatic self-assembly from polyelectrolyte aqueous solutions of different ionic strengths. The growth of the multilayers has been followed using dissipative quartz crystal microbalance and ellipsometry. Neutron reflectometry and XPS data indicate that the PSS and PDADMAC layers interpenetrate leading to an almost homogeneous polymer film. The results show that on increasing [NaCl] the growing process changes from a linear to a non-linear regime. The comparison of the thickness values obtained from QCM and ellipsometry has allowed us to calculate the water content of the polymer film. The results agree with those obtained by neutron reflectometry. The analysis of the QCM data has provided values of the complex shear modulus, which are typical of a rubber-like polymer system. The analysis of the mass adsorbed calculated by the ellipsometry measurements indicated that the charge compensation mechanism changes from intrinsic at low ionic strengths to mainly extrinsic at high ionic strengths. Finally, it was found that the response of a polymer film to a change in [NaCl] is rather different for films grown at low or at high ionic strengths.