The UV protective coatings, prepared by the Sol-Gel method, are based on organic UV absorber molecules in modified silica matrices (ormosil) and are capable to reduce drastically the UV light reaching the substrate that needs to be protected, and hence its photodegradation upon prolonged exposition to UV sources.

On the other hand, the coating should not affect the optical properties of the substrate in the visible range of the spectrum. There is a wide range of materials made up with organic components whose applications in industry are limited due to their rapid photodegradation upon exposure to artificial or solar radiation. The ability to increase the durability of outdoor products, that can withstand uncoated the solar radiation for months or years, by a factor which makes the protective coatings very attractive to be used in commercial applications. These materials go from paints, dyes and plastics in outdoors applications to artwork pieces in museums, that are exposed to prolonged irradiation.

Left picture- Coatings can protect artwork from UV damaging; Right picture- Photodegradation of a fluorescent film coated (up) and uncoated (bottom) with the protective film

Materials scientists in Spain have used sol-gel technology to develop a UV protective coating, which they say can protect organic materials from light damage.

David Levy and colleagues at the MSI, inserted a benzophenone into ormosil, an organically modified silica that forms well-defined porous networks. The benzophenone chosen has good photostability and strong UV absorption capability. Ormosil is an ideal substrate because its porosity allows high loading, and it can be modified at room temperature. The resulting matrix creates a transparent UV protective coating without the often encountered problem of high temperature curing.D. Levy found that photodegradation rates of a fluorescent dye were 14 times slower after it had been coated with the ormosil-benzophenone composite.

Photodegradation occurs when organic materials susceptible to decomposition are exposed to light. Artificial light, such as flash photography, can be just as damaging as sunlight. The resulting matrix creates a transparent UV protective coating without high temperature curing.

The ormosil-benzophenone coating is effective because it absorbs and dissipates UV radiation before it reaches the organic material. D. Levy added that, it can be applied to almost any material exposed to strong light sources. It could even be used to protect artwork in museums from flash photography.

C. Liauw welcomed the work and he said that, this is a novel approach to UV protection that places the UV absorber exactly where it is needed.

The research result on "Highly efficient UV-absorbing thin-film coatings for protection of organic materials against photodegradation" by Pilar Garcia Parejoab, Marcos Zayata and David Levy is as follows
UV-protective coatings have been prepared by the sol–gel method, to reduce the destructive effects of UV radiation on easily photodegradable devices, i.e. those containing organic compounds, such as dyes and pigments or plastic materials to be used in outdoor applications. A benzophenone derivative (2,2-dihydroxy, 4-methoxybenzophenone), showing high photostability and strong absorption in the UV range, was embedded in an ormosil matrix. The usage of an organically modified silica matrix enhances the solubility of the UV absorber in the matrix allowing the preparation of highly loaded coatings. The protective coatings, prepared at room temperature, require no thermal treatment after deposition, allowing therefore their application on temperature sensitive materials. The resulting films have a strong absorption in the UV range with a thickness of only 1.0 µm. In addition, the UV-absorbing coatings are transparent, colourless, and exhibit high optical quality. The UV-protective coatings offer an easy method to prevent the photodegradation of organic materials without altering their optical properties in the visible region.

Fluorescent rhodamine dye-doped thin ormosil films were coated with a UV-protective layer in order to study their effectiveness in the reduction of the photodegradation of the dye upon irradiation with UV light. The degradation of 20% of the molecules in coated samples was 14 times slower than that of the uncoated samples. The effective temperature range of the UV-protective coatings was established by measuring the photodegradation of the samples at different temperatures.