Mechanical properties of nanocomposite organosilicate films

Nanocomposite coatings have been deposited on plastic substrates by the dip ping-drawing technique. The coatings were constituted by a matrice of a hyb rid organomineral gel and a reinforcement made of amorphous silica. Two met hods by which increase the silica content were investigated: silica was add ed via a silicon alkoxide compound or via dense silica particles of 10 nm s ize. Young's modulus and the hardness of the coating were measured using ho me-built equipment, and results compared to literature models. It is shown that the agreement between models and experimental values depends on the me thod of preparation of the nanocomposite coating. On the other hand, deviat ions appear when the volume fraction of reinforcement surpasses the three-d imensional percolation threshold. (C) 1998 Kluwer Academic Publishers.