| Summary: | Two types of coating materials were prepared by a sol-gel process and classified into two systems. In system I, four different types of the optically transparent organic-inorganic hybrid coating materials produced by The Welding Institute (TWI) using a patent method called Vitresyn, identical in terms of the precursors, but different in terms of their relative proportions, were examined. The precursors used for system I were tetraethoxysilane (TEOS), 3-(trimethoxysilyl)propyl methacrylate (MPTMA) and an aliphatic urethane acrylate. The coating materials were deposited on aluminium, brass and polycarbonate substrates by a flow coating method, and cured under a UV lamp for various times from 2 minutes to 40 minutes. In system II, MPTMA, Methyltrimethoxysilane (MTMS) and trimethoxysilypropyl acrylate (PATMS) were used as precursors. No urethane acrylate was used in this system. TEOS was used in system I as the primary inorganic precursor and urethane acrylate was used as the source of organic component. MPTMA was used as both a secondary inorganic source and a coupling agent between the organic and inorganic phases. To ascertain the interaction relationships between organic and inorganic phases in the hybrid materials, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR) were used. It was found that a siloxane (SiO-Si) network is a backbone of the hybrid materials and that the network increases with increasing inorganic content in the hybrid materials. These organic-inorganic hybrid materials were mainly cross-linked by T<sup>3</sup>, Q<sup>3</sup> and Q<sup>4</sup> species. It was also found that UV curing leads to accelerated condensation reaction through the opening of C=C bonds in MPTMA and urethane acrylate. Microstructures in the coatings and interfaces between the coatings and the substrates were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coating thickness is dependent on the relative amount of organic resin added to the hybrid materials. The coating thickness increases as more organic resin (urethane acrylate) is used. Neither silica domains nor pores were observed in the coatings. It was concluded that the hybrid coating materials are a single featureless amorphous phase regardless of the organic/inorganic ratios. Scratch testing was used to study the scratch resistance of the hybrid materials and the interfacial strength between the coatings and the substrates. A micro-indentation adhesion test using focused ion beam (FIB) technologies was also used for investigating interfacial strength. The results showed that scratch resistance increases with an increase in the relative amount of organic resin added.
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