On the deposition and properties of DLC protective coatings on elastomers: A critical review

In this paper we will critically review various strategies for a successful deposition of highly adherent protective coatings on elastomers and rubbers. Emphasis will be placed on the differences with traditional approaches that are explored on rigid substrates (e.g. steel or silicon). Although we will focus on protective coatings, the generic ideas are also applicable for the deposition of any thin film on flexible polymers. The method for fine tuning the coating microstructure via a proper selection of the deposition conditions will be elucidated afterwards. Since the protection of rubber substrate is the major application of these coatings, the performance as protective films will be discussed in detail. Particular attention will be given to the friction coefficient and the influence of the viscoelastic properties of substrate. A comprehensive model explaining the influence of the parameter set is presented. Finally, the main conclusions of the work and the open questions for future explorations are briefly outlined. In general, an excellent adhesion is the critical requirement to reach optimal protection of the substrate. The frictional performance can be optimized depending on the viscoelastic properties of the rubber, the microstructure of the coating and the conditions of the contact.