  In this study, we investigated the thermodynamic features of a system based
on oppositely charged polyelectrolytes, sodium alginate, and
poly(diallyldimethylammonium chloride) (PDADMAC) at different pH values.
Additionally, a comparison of the effects of the thermodynamic parameters on
the growth of the layers based on the same polymers is presented. For this
investigation, different techniques were combined to compare results from the
association in solution and co-assembled layers at the silicon surface. Dynamic
light scattering (DLS) and isothermal titration calorimetry (ITC) were used for
studies in solution, and the layer-by-layer technique was employed for the
preparation of the polymer layers. Ellipsometry and atomic force microscopy
(AFM) were used to characterize the layer thickness growth as a function of the
solution pH, and interferometric confocal microscopy was employed to analyze
the topography and roughness of the films. The layers grown for the
PDADMAC/sodium alginate system demonstrated pH sensitivity with either linear
or exponential behavior, depending on the pH values of the polyelectrolyte
solutions. The layer thicknesses measured using ellipsometry and AFM data were
in good agreement. Additionally, a pH influence on the roughness and topography
of the films was observed. Films from basic dipping solutions resulted in
surfaces that were more homogeneous with less roughness; in contrast, films
with more layers and those formed in a low-pH dipping solution were rougher and
less homogeneous.
