Annealing and ultraviolet treatment of plasma fluorocarbon films for enhanced cohesion and stability

Abstract

Stents, commonly used for the treatment of cardiovascular diseases, are mainly made of 316L stainless steel. They are, however, prone to corrosion when they are in contact with human body fluid. To prevent this corrosion process and to ameliorate their patencies, in this study, we used a strategy to cover stent materials with a protective fluorocarbon layer deposited by plasma polymerization. In an approach to optimize its cohesion properties and stability, posttreatments, namely, thermal annealing and UV irradiation, were applied on the ultrathin fluorocarbon film. A combination of X-ray photoelectron spectroscopy, polarized near-edge X-ray absorption fine-structure spectroscopy, and time-of-flight secondary ion mass spectrometry demonstrated that UV treatment led to chain scission and film crosslinking and, in this way, decreased the amount and/or size of nanoscaled defects originally present in the films. Annealing on the other hand induced a film reorganization in favor of longer, well-ordered fluorocarbon chains. However, a deformation process that was applied to study the film adhesion properties induced chain scissions with reorganization. Aging tests exhibited an oxidation of the topmost layer for both the as-deposited and posttreated samples. Finally, the film stability was improved after UV treatment for both the nondeformed and deformed samples.

Influence of the 316 L Stainless Steel Interface on the Stability and Barrier Properties of Plasma Fluorocarbon Films

“…Therefore, the etching induced a highly sensitive interface and water infiltration through nanopinholes in the coating led to a more important reoxidation. Nanopinholes have been evidenced by previous NEXAFS analyses . Moreover, Wambach et al showed that the oxidation rate of the stainless steel was about 10 times higher in water than in air, which could explain the fact that the oxide layer enlargement caused by aging exceeds the thickness of the native oxide layer.…”

“…In this context, CF x plasma deposition on SS316L has been investigated and previous results showed promising adhesion properties for the fluorocarbon films after a plastic deformation similar to a stent expansion. − Previous characterizations by near-edge X-ray absorption fine structure (NEXAFS) showed the occurrence of nanodefects, which led to water diffusion during immersion in aqueous medium and resulted in chemical modifications and reorganization of the coating . To lower the nanodefects density, to promote the film growth and to increase the film stability, we applied different plasma etching sequences prior to the coating deposition.…”

Fabrication of polytetrafluoroethylene–carbon nanotube composite coatings for friction and wear reduction

“…The PTFE in the coating layer retained its powder shape due to water evaporation during the spin coating process and had a noticeably poor adhesion and durability. This outcome was expected because PTFE exhibits low adhesion with the substrate when coated using the spin coating method alone . Furthermore, the measurement of contact angle which has a strong dependency on macroscopic properties showed that the coatings were not hydrophobic, which is one of the properties and advantages of PTFE.…”

“…Furthermore, the measurement of contact angle which has a strong dependency on macroscopic properties showed that the coatings were not hydrophobic, which is one of the properties and advantages of PTFE. Since it is well accepted that macroscopic properties of multiphase composite materials depend on the interfacial bonding strength of the matrix and the reinforcing phase , the PTFE coatings prepared by the spin coating method needed to be subsequently processed through a post‐treatment method such as heat treatment to improve their integrity .…”

Partial secondary electron-yield NEXAFS spectromicroscopy with an energy-filtered X-PEEM

“…X-ray photoemission electron microscopy (X-PEEM) is used by many groups to study Bsoft[ surfaces, such as those associated with bio-adhesion phenomena and the structure of organic thin films [1][2][3]. X-PEEM can be used to extract near-edge x-ray absorption fine structure (NEXAFS) spectra of the near surface region of a sample ($5 nm deep [4]) with the high lateral spatial resolution of PEEM.…”