Polydimethylsiloxane-Based Composites with Photo-Autocatalytic Properties: Surface Photooxidation, Hydrophobicity, and Nanomechanical Properties.

A synergistic approach to the photodegradation of polydimethylsiloxane-based composites upon photoaging was implemented by using La(III) complexes of Schiff base ligands with a silicon-containing spacer as fillers. The analysis methods were spectral, nanomechanical, and morphological. The results show that the accelerated oxidative degradation of the polydimethylsiloxane matrix is due to the combined actions of radicals, fragments, and photoproducts derived from the photolysis of the La(III) complexes and the water vapors in the photoaging chamber. Compared to the undoped polydimethylsiloxane, the photo-excited radical intermediates and photoproducts of the La(III) complexes, with aromatic or quinone structures, in ground or in excited state, have acted as photocatalysts and as new sources for reactive intermediates and for the generation of reactive oxygen species. Infrared, electron spin resonance, and nanomechanical investigations revealed that the chemistry of the photoaged surfaces comprises oxygen-containing species, photoreaction products, and an extended siloxane network with embedded ligand fragments. The key role of La(III) complexes in promoting the generation of reactive species is described. The study highlights the unexplored potential of La(III) complexes of Schiff base ligands bearing a silane/siloxane spacer as potential catalysts in the photodegradation of polymers and plastics.