DIC contrast present but unexpected

[loukote]

Hello,

i had rubber sample made from two rubber components/compounds. The interface between the components was not visible in reflected light on a guillotine cut, and it was not visible on a polished section. (Polished similarly as a metallurgical sample. Polishing resulted in a nearly plane and slightly inclined surface.) Neither dark-field nor polarized-light could resolve the interface -- one colour across the whole sample.

From the above, i was assuming that there is no step in between the components (dark-field) and that the compounds give the same reflection in polarized light. So DIC should not show the interface. I tried anyway and was surprised to see two different colours on both sides of the interface.

See images attached. The microscope was the following: Zeiss AxioImager Z2 Vario, objective 10×/0.30 Epiplan Neofluar HD. (Not a DIC dedicated/meant objective.)

I'd like to understand why DIC shows a different colour. The literature did not help. I must be missing something. Could you help to explain why DIC results in two homogeneous regions with a distinct colour contrast?

Many thanks,
Ondrej

bright field

BF.jpg (371.21 KiB) Viewed 3150 times

dark field

DF.jpg (409.27 KiB) Viewed 3150 times

DIC

DIC.jpg (364.48 KiB) Viewed 3150 times

[gekko]

Sorry you didn't get a reply, the reason, I think, is that no one has a good answer. One answer might be that the optical properties are different in the two parts, but that clearly does not answer your question, rather it restates your question. Perhaps someone who studies the physical properties of rubber may be able to help you.