Sometimes you can tell with your eyes. While I dont deal with polyacrylate, Viton seals have a some subtle visual clues vs. a nitrile seal. Viton has a slightly lighter color and a graininess to its appearance. If you can compare to known seals you might be able to distinguish a difference.
There are kits that use different gravity oils that can help identify elastomer based on density.
Another method might be to find a chemical that will swell or soften one but not the other. For example, Viton is relatively unaffected by ethanol while AEM likely is.
The best way, however, is to toss them in the garbage and order new ones and don't mix them up this time.
