at the material’s surface. Figure 1(b) is a photograph of the
back of the two samples shown in Figure 1(a). The difference
in color between irradiated and nonirradiated samples is far
less pronounced.The nominal cross sectional thickness of the
filmsonthe slide is about 0.75mm(Figure 1(c)). 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.