Crystalline PEO when under crossed polars shows distinct Maltese cross pattern. Being birefringent, when polymer crystal align with the polarizer or analyser it shows extinction regions (effect known as zero amplitude extinction). And as PEO crystallize in spherulites, it does lead to Maltese cross pattern. (As parallel and perpendicular crystal fibrilis lead to extinction). Because the fibrilis twist upon radial growth it also leads to banded extinction regions, known as zero birefringence extinction.
Upon melting, first the crystal fibrilis realign themselves enhancing contrast of crystalline spherulite, and then I can observe some of the colours appearing in the banded structure, that I haven't seen before. Why does it happen?
