Fabrication of polyelectrolyte/amine-modified silica composite thin film by coupling of layer-by-layer assembly and sol–gel techniques

This study focuses on a facile approach to create polyelectrolyte/SiO₂ composite thin films. The film was fabricated by alternate deposition of N-[3-(trimethoxysilyl)propyl]diethylenetriamine (C₁₀H₂₇N₃O₃Si, TPDT in short) and poly(acrylic acid) (PAA). The layer-by-layer assembly process was accompanied by sol–gel transition of TPDT. The resultant films were investigated in detail by Fourier transform infrared spectroscopy (FT-IR), UV-Visible spectroscopy (UV–vis), ellipsometry, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the films grew exponentially with increasing bilayer number. During deposition, hydrolysis and condensation of silanol groups in the film resulted in the formation of a Si-O-Si network embedded into the framework of the polymer. The obtained free-standing films had high transparency even with a high content of silica, and showed good mechanical properties with a tensile strength of 32.8 MPa at break.