Dichromated photosensitive materials: involvement of the polymeric matrix

Irradiation of dichromated polyvinyl alcohol and dichromated polyacrylic acid DC(PVA-PAA) at 365 nm was investigated in order to understand the involvement of the polymeric matrix in the reduction process of the Cr(VI) leading to the formation of the hologram. The photochemical evolution of the matrix was directly correlated to the disappearance of the absorbing species, chromium(VI). A special attention was paid to the absorption profile of the films. Due to the impermeability of the polymer, no oxidation proceeded. The reduction of Cr(VI) into Cr(V) induced the formation of carboxylate species perfectly correlated with the consumption of carboxylic groups. Besides the acido-basic reaction undergone by the carboxylic groups, the reduction of Cr(VI) provoked the cross-linking of the polymer. Each polymer appears to play a specific role in the mechanism.