Staining of water trees with methylene blue explained

Staining with a methylene blue solution, a popular technique for achieving the required high contrast images of water trees, was carried out at 70°C. It is shown that methylene blue stains the complete tree, which justifies water tree length measurements after staining. The water tree is not stained exclusively, but rather faster and probably to a higher degree than the polyethylene. Comparing optical microscopy images of water trees before and after staining, it was found that the entire tree becomes visible. Comparison of FTIR (Fourier-transform infrared) spectra measured before and after staining did not indicate that a chemical reaction is required in the staining process. In general, the staining of water trees with methylene blue can be explained by mere diffusion. The enhanced temperature of 70°C helps to increase the permeability of the polyethylene