Structuring of poly(DADMAC) chains in aqueous media: a comparison between bulk and free-standing film measurements

Abstract

Recently, thin film balance (TFB) measurements have shown that foam films (thickness 5–120 nm) containing polyelectrolytes thin stepwise. This was connected to the ordering of the polyelectrolyte chains in the film, since pure foam films thin in a continuous way. The present paper shows disjoining pressure isotherms of films containing the polycation poly(DADMAC) and small angle neutron scattering (SANS) spectra of the corresponding aqueous solutions at different polyelectrolyte concentrations. The steps Δh in the isotherms are of the same size as the correlation length ξ in the bulk solution. This leads to the conclusion that the interactions between the polyelectrolyte chains which are responsible for their structuring in the bulk determines also the stratification behavior of polyelectrolyte/surfactant films. These findings were confirmed by the influence of further parameters like the molecular weight, the ionic strength and the degree of charge. The results of the TFB measurements and the SANS experiments show the same dependence on these parameters.