Organically modified silica based nanomaterials for functional surfaces

Abstract

Organically modified silicas (ormosils) are unique materials due to their combined properties achieved from organics and inorganics. Ormosils contain at least one non-hydrolysable organic groups which results in a decrease of rigid Si-O-Si bonds, introducing a flexible character. Therefore, ormosils exhibit both flexibility of organics and atmospheric stability of inorganics. Organic group determines the functionalities of ormosils, thus their properties can be adjusted by choice of appropriate organic modification. Ormosils can be easily prepared in mild conditions of sol-gel technique, and can be applied on different surfaces by low cost and simple techniques. In this thesis, we prepared superhydrophobic-superhydrophilic, antireflectiveantifogging, anticorrosion and antiicing (ice retarding) functional surfaces using organically modified silica and its nano-composites in thin film form. Methyltrimethoxysilane (MTMS) is used in the synthesis of all films due to its intrinsically hydrophobic nature. This monomer is found to enable porous film formation without any modifications at ambient temperature and pressure. Superhydrophobic ormosil aerogel films with water contact angles reaching 179.9 and porosity of 86 % have been prepared using phase separated colloidal suspensions of MTMS, which exhibited flexibility, thermal stability and superhydrophilic transition after annealing at 600 C. Antireflective films with high mechanical stability are prepared from co-condensation of MTMS with tetraethylorthosilicate monomer, which exhibited transmission as high as 99.6 % with flexibility and transition to antifogging after annealing at 600 C. Anticorrosion films for glass surfaces have been prepared by encapsulation of ZnO and ZrO2 nanoparticles to yield nano-composites of porous and nonporous ormosil films, which resulted in four times less corrosion compared to bare glass and acts as a barrier layer for corrosion of glass substrates against alkaline corrosion. In formation of antiicing coatings various combinations of ormosil films mentioned are used and correlation between contact angle, stability of contact angle against cooling, surface roughness and freezing times are investigated. Compared to bare glass, freezing times are increased two order of magnitudes.