Chemical resistance of DLC thin film deposited PMMA substrates

DLC thin films were deposited on silicon and poly(methyl methacrylate) (PMMA) substrate using a plasma chemical vapor deposition method with a negative bias voltage of 200 V applied to the substrate, and investigated for the chemical resistance to acetaldehyde, acetone, acetic acid and sodium hydroxide by an immersion test. Raman spectra and nano-indentation hardness measurement showed high stability in the DLC structure and mechanical property against the immersion into organic solvents, acid and alkali solutions. The decrease in Raman spectra peak intensities, before and after the immersion into acetaldehyde and acetone, was reduced by the DLC thin film deposition on the PMMA substrate, and the effect of DLC coating was revealed. A scanning electron microscope (SEM) observation from the PMMA substrate surface and cross section, with and without the DLC coating and before and after the immersion into acetone, suggested that the DLC layer protected the dissolution of PMMA into acetone by preventing the molecules of acetone from contacting with the surface of PMMA and penetrating into the PMMA.