Self-assembled multilayer films based on dendrimers with covalent interlayer linkage

Multilayer ultrathin films composed of nitro-containing diazoresin (NDR) as polycation and poly(amidoamine) dendrimers with carboxyl terminal groups (PAMAMC) (G = 1.5, 2.5, 3.5, and 4.5) as polyanion were fabricated on mica by electrostatic layer-by-layer deposition. Subsequent UV irradiation converted the interlayer linkage from ionic to covalent. The films were characterized with UV-vis, FTIR, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results show that the uniform multilayer films were formed. All the films with dendrimers of various generations as building blocks have a very smooth surface with a mean roughness of about 0.8-1.1 nm. The thickness of the PAMAMC-NDR bilayer in the films increases with the generation number of the dendrimer, but the average thickness of the dendrimer monolayer is smaller than the diameter of the ideal spherical model of dendrimers with an extended conformation of all branches. They are significantly compressed in multilayer films. The conversion of the ionic to covalent linkage dramatically improved the stability of the films with respect to polar solvent, strong electrolyte, and surfactant solutions.