Required compatibility with fullerene pigment, high as possible transmittance to infrared radiation, heat resistance and good mechanical behaviour lead to select epoxy silicone resin as binder which, with adequate additives to confer enough strength and durability to the final paint, forms the paint base.

The paints were prepared from epoxy silicon resin that was previously mixed with charges and additives. Three types of pigments were used: a mix of C60/C70 fullerenes, copper powder (particle size 63 and 90pm), and stainless steel powder with particle size of 3 pm. The introduction of the pigments in the initial base paint was made with the admixing of the pigments in a solution of the resin and n-butyl acetate in a rotating disperser at a constant speed of 700rpm min-1 until a

granulometry of 12pm was reached. The paints were applied to a copper substrate by a draw bar coater and by a spray technique in order to achieve thin coatings with lower thickness.

Some painted samples with paint including organic pigments, were submitted to accelerate aging tests, with exposure to UV radiation, in humidity conditions with accordance of ASTM G 154 standard and also of strength to humidity following the standard NB ENISSO G 270-1.

3. Results and discussion

Nanostructured multilayer thin films with titanium oxide already were subject of our work [4], but to avoid multilayer production complexity and eventually atomic diffusion between layers with time, at high temperatures, one of our present goals is to optimise optical properties of monolayer titanium oxide thin films with adequate thickness, composition and morphology, complemented in terms of absorption increment by organic pigment impregnation. For impregnation adequate pigments have to be selected in order to have absorption peaks located in solar spectrum and preferentially in wavelength range where our optimised titanium oxide film have less absorption.

On the basis of this strategy we prepared pigment-adsorbed single-layer TiOx thin films using a natural dye extracted from Sambucus nigra L.[3] (a mixture of anthocyanins) with an absorption maximum of 530nm. Anthocyanins belong to a group of natural dyes found in fruits, flowers and leaves of plants. Because anthocyanins show the color in the range of visible light from red to blue, it is prospected to become a high efficient sensitizer for a wide bandgap semiconductors. Due to the carbonyl and hydroxyl group presented on anthocyanin molecule [3], it can be bound to the surface of titanium dioxide porous film to produce sensitized TiO2 thin films for dye-sensitized solar cells (DSSC) applications [18].

However applied chemically over optimised titanium oxide coating, didn’t improve significantly solar absorption, but best titanium oxide coating, with one layer, graded in terms of oxygen content, have 88% of absorption and 7% of thermal emissivity, and we hope that absorption could be improved with a final very thin layer with less refractive index.

Pursuing the objective of low cost, easy application, high solar absorption and durability, with a minimum possible of thermal emissivity, work was also done with formulation of paints with organic pigments (C60/ C70) and with organic and inorganic pigment (Cu and steel), having epoxy silicon resin as binder, with higher transmittance to thermal infrared radiation. The paints obtained showed emissivity values sensitive to the thickness, with the best couple values for absorption, emissivity of 96%, 74% respectively, these achieved for paint with organic pigment and average thickness coating of 4pm, the minimum thickness attained by spray application over copper substrate.