Examination
of the film cross sections with a light microscope (Olympus
BX43) suggests that the color change penetrates less than 20%
of the film thickness. Incubation of the irradiated material
at 45∘C in an aqueous solution dissolves the uncolored
portion, leaving only a thin sheet of hydrated thermostable
product.Theobserved color of the irradiated sample is mostly
removed upon incubation in water. This suggests that the
compound responsible for the color change is a byproduct of
the cross-linking reaction and is not strongly associated with
the newly cross-linked molecular arrangement. The exact
compound requires further analysis.