Shedding light into adhesive optimization of material interfaces by plasma treatment

The adhesion of sealants to mortar or concrete is an important feature especially in building joints and the durability of the joints over a long period is an essential goal. In the present work, the surface of a cement mortar substrate is plasma treated by means of a dielectric barrier discharge. It is shown that the adhesion to a silicone sealant is improved by the plasma pretreatment. For this purpose, tensile strength tests were carried out. Furthermore, the molecular pictures behind this adhesive optimization are investigated. The plasma-treated surface was analyzed by Raman and X-ray photoelectron spectroscopy. It has been found that the plasma causes chemical modification of the substrate surface resulting in particular in a decrease of carbonate groups and a simultaneous increase of calcium oxide and probably calcium hydroxide. The improved adhesion is attributed to the formation of covalent bonds with the silanol groups of the silicone sealant and to an increase of hydrogen bonding.