No abstract

Poly(dimethylsiloxane) (PDMS) substrates are used in many applications where the substrates need to be elongated and various treatments are used to regulate their surface properties. In this article, we compare the effect of three of such treatments, namely, UV irradiation, water plasma, and plasma polymerization, both from a molecular and from a macroscopic point of view. We focus our attention in particular on the behavior of the treated surfaces under mechanical stretching. UV irradiation induces the substitution of methyl groups by hydroxyl and acid groups, water plasma leads to a silicate-like layer, and plasma polymerization causes the formation of an organic thin film with a major content of anhydride and acid groups. Stretching induces cracks on the surface both for silicate-like layers and for plasma polymer thin coatings. This is not the case for the UV irradiated PDMS substrates. We then analyzed the chemical composition of these cracks. In the case of water plasma, the cracks reveal native PDMS. In the case of plasma polymerization, the cracks reveal modified PDMS. The contact angles of plasma polymer and UV treated surfaces vary only very slightly under stretching, whereas large variations are observed for water plasma treatments. The small variation in the contact angle values observed on the plasma polymer thin film under stretching even when cracks appear on the surface are explained by the specific chemistry of the PDMS in the cracks. We find that it is very different from native PDMS and that its structure is somewhere between Si(O2) and Si(O3). This is, to our knowledge, the first study where different surface treatments of PDMS are compared for films under stretching.

High interfacial strengths of elastomer to metal joints imply the formation of covalent bonds at the interface. It is proposed to deposit a plasma polymer coating containing double bonds on an aluminium substrate for the formation of crosslinks between the elastomer and the coating during peroxide crosslinking of the elastomer. Ethylene-co-propylene-co-diene terpolymer (EPDM) is considered here. Maleic anhydride is polymerised and reacted with allylamine to lead to an amide functionalised plasma polymer which is heated to produce imide functional groups. Plasma polymer coated aluminium=EPDM joints were evaluated by a peel test and the locus of failure was identified by several techniques: SEM, infrared spectroscopy, wettability, and XPS.