Covalently attached multilayer assemblies by sequential adsorption of polycationic diazo-resins and polyanionic poly(acrylic acid)

Diazo-resins (DAR) as polycation and poly(acrylic acid) (PAA) as polyanion were alternately assembled into a multilayer structure by using the layer-by-layer self-assembly technique. PAA as a weak polyelectrolyte was very sensitive to the pH value of the solution, and that pH could be used to tune the thickness of the PAA layer. Upon UV irradiation, a fraction of the carboxylate groups reacted with diazonium groups at the adjacent interfaces of the multilayer, so partially covalently attached multilayer assemblies could be formed. Their stability improved greatly compared with the fraction that was not UV-irradiated. The photoreaction occurring between the layers was confirmed by means of UV-visible and Fourier transform infrared spectroscopy. The thickness of the W-irradiated films was characterized with X-ray diffraction, results from which showed that the thickness of the films can be adjusted in nanometer scale by simply changing the pH value of the solutions.