Alumina coatings on PMMA: optimization of adherence

Alumina is deposited on polymethyl methacrylate (PMMA) using the RF magnetron sputtering method. The adhesion is characterized by means of a 180° peeling test and a fragmentation test. The surface energy of the materials is determined by measuring the contact angles using the two liquids method. The plasma surface treatment of the polymer help to smooth it and increase its surface energy. The modifications of the dispersive and polar components of this energy depend on the type of the plasma-gas used. Oxygen rich plasmas, such as air or carbon dioxide, allow the surface polarity of the polymer to be increased by a superficial oxidation whilst limiting the reticulation. They give better adhesion values. The analysis by ATR-FTIR displays the reticulation phenomenon for the extended application of argon plasma at low power. The RBS analysis shows that the quantity of argon incorporated into the alumina deposit is dependent on the operating conditions, particularly the pressure in the sputtering chamber. Different values of surface energy are due to the variations in composition. The alumina films with the lowest percentage of argon have the highest polar component. Their adhesion to the PMMA is also the highest. The best adhesion of alumina on PMMA is obtained for a polymer activation during a short time (10 s), by means of an oxygen rich plasma (CO₂) and for alumina coatings which have the lowest argon content (p = 1 Pa).