Abstract
Siloxane based coatings with two different precursors (HMDSO: hexamethyldisiloxane and TEOS: tetraethylorthosilicate) have been fabricated in a two-step process using atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD) on ethylene-propylene-diene terpolymer (EPDM) and NBR (nitrile butadiene rubber) to reduce stick slip and wear of the elastomer surfaces.
The influence of roughness and chemical composition on wetting and frictional properties have been investigated. Topography analysis using scanning electron microscopy (SEM), white light interferometry (WLI), and digital microscopy was combined with surface analytical methods, such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) as well as contact angle, friction, and wear experiments were performed to obtain a very detailed understanding of the plasma polymer surfaces. The different plasma coatings made it possible to adjust the wettability, surface energies, and friction of different elastomers, which are important for different applications.
The contact angle investigations have shown that both coatings (HMDSO and TEOS) are more polar compared to the untreated surface, but less polar than the surface activated EPDM without precursor. As shown by XPS studies, the carbon content decreases, and the oxygen and silicon content increased after plasma polymerization. ToF-SIMS studies indicated that the two coatings had comparable surface chemistry. The surface energy of the activated EPDM surface without precursor increased significantly compared to the untreated EPDM due to incorporation of polar groups into the surface. Both coatings with the corresponding precursors also had higher surface energy than the uncoated EPDM, with the TEOS coating having higher surface energy than the HMDSO coating. Both coatings had a lower surface energy than the activated EPDM. Friction and stick-slip can be significantly reduced with both plasma polymer coatings. The lowest friction values with simultaneous absence of stick-slip on EPDM were achieved by using the precursor TEOS as a friction partner.
The influence of roughness and chemical composition on wetting and frictional properties have been investigated. Topography analysis using scanning electron microscopy (SEM), white light interferometry (WLI), and digital microscopy was combined with surface analytical methods, such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) as well as contact angle, friction, and wear experiments were performed to obtain a very detailed understanding of the plasma polymer surfaces. The different plasma coatings made it possible to adjust the wettability, surface energies, and friction of different elastomers, which are important for different applications.
The contact angle investigations have shown that both coatings (HMDSO and TEOS) are more polar compared to the untreated surface, but less polar than the surface activated EPDM without precursor. As shown by XPS studies, the carbon content decreases, and the oxygen and silicon content increased after plasma polymerization. ToF-SIMS studies indicated that the two coatings had comparable surface chemistry. The surface energy of the activated EPDM surface without precursor increased significantly compared to the untreated EPDM due to incorporation of polar groups into the surface. Both coatings with the corresponding precursors also had higher surface energy than the uncoated EPDM, with the TEOS coating having higher surface energy than the HMDSO coating. Both coatings had a lower surface energy than the activated EPDM. Friction and stick-slip can be significantly reduced with both plasma polymer coatings. The lowest friction values with simultaneous absence of stick-slip on EPDM were achieved by using the precursor TEOS as a friction partner.
