Silica-based photonic crystals embedded in a chitosan-TEOS matrix: preparation, properties and proposed applications

Our research involves the development of a pH-sensitive chitosan-tetraethyl orthosilicate interpenetrating polymer network (Chi-TEOS IPN) suitable for the introduction of ordered silica nanoparticles. The pH-sensitive properties of the IPN provide an innovative framework for ordered colloidal silica (SiO₂) films known as photonic crystals. The pH-sensitive properties of chitosan occur naturally due to its cationic polyelectrolyte structure; cross-linking with TEOS provides mechanical strength and incorporation of the silica photonic crystal provides a means of optical detection for a pH-driven expansion mechanism. Chitosan-tetraethyl orthosilicate-silica (Chi-TEOS-SiO₂) composites are formed through a three-step mechanism in which the silica photonic crystal and Chi-TEOS IPN hydrogel are synthesized separately and then combined to form the Chi-TEOS-SiO₂ composite. The silica photonic crystals, IPN membranes and final composite structures were analysed separately through optical, mechanical and swelling studies. Through the successful fabrication of a Chi-TEOS-SiO₂ composite we propose a membrane suitable for applications in environmental, chemical and biological sensing of pH.