Direct Imaging of Mechanical and Chemical Gradients Across the Thickness of Graded Organosilicone Microwave PECVD Coatings

Abstract

The characterization of variations in the chemical composition and ensuing mechanical properties across the thickness of coatings with continuously varying compositions through their thickness (graded coatings) presents considerable challenges for current analytical techniques in materials science. We report here the direct imaging of nanomechanical and chemical gradients across cross-sections of an organosilicone coating fabricated via microwave plasma enhanced chemical vapor deposition (PECVD). Cross-sectional nanoindentation was used to determine the mechanical properties of uniform and graded organosilicone coatings. Both hardness and modulus across the coatings were directly measured. Additionally, "modulus mapping" on cross-sections was used to map the complex modulus. For the graded coating, it was found that variations in the complex modulus was predominantly due to varying storage modulus. It was observed that at the interface with the substrate there was a low storage modulus, which linearly increased to a relatively high storage modulus at the surface. It is proposed that the increase in stiffness, from the substrate interface to the outer surface, is due to the increasing content of a cross-linked O-Si-O network. This mechanical gradient has been linked to a change in the Si:O ratio via direct compositional mapping using ToF-SIMS. Direct mapping of the mechanical and compositional gradients across these protective coatings provides insight into the changes in properties with depth and supports optimization of the critical mechanical performance of PECVD graded coatings.

Evaluation of polymer hydrophobic recovery behavior following H2O plasma processing

“…Polymers find extensive use in many important modern industries, including automotive, biomedical, environmental, and laboratory applications . Often, however, the properties of the polymer surface, including surface tension and surface functionality, are incompatible with the intended application, thereby limiting their utility.…”

“…Often, however, the properties of the polymer surface, including surface tension and surface functionality, are incompatible with the intended application, thereby limiting their utility. Among the most common issues, adhesive failure and delamination are resulting from interface incompatibility, wetting and fouling issues arising from undesirable surface tension or surface functionality, and surface instability causing the polymer surface to denature or degrade . Each of these issues can be mitigated by surface modification processes, including exposure to ultraviolet radiation, flame treatment, and plasma surface modification .…”

Chemical seeding via propanol plasma pretreatment for improving adhesion and properties of PECVD siloxane coatings on polymers

“…As previously mentioned, the graded siloxane coatings are not homogeneous throughout their thickness, and it has been shown previously that the mechanical properties and RI are also graded as a result. Modelling of the thickness via the filmetrics resulted in an average RI being calculated, whilst simpler this method still resulted in meaningful results.…”

“…The deposition utilised tetramethyldisiloxane (Flexichem, Australia) at a constant gas flow of 80 sccm. The flow rate of oxygen was controlled during the deposition to create a graded coating under the following flow rate conditions: initial flow of 100 sccm for 2 s, linear ramp from 100 to 400 sccm over 20 s and a final flow rate of 400 sccm for 20 s. This gave an average coating thickness of 3.0–4.0 μm. Samples were stored in laboratory conditions at 22 °C with a relative humidity of between 30 and 60%.…”

“…In this study microwave PECVD was used with tetramethyldisiloxane (TMDSO) and oxygen, mixed as process vapours to deposit a siloxane coating onto a plastic substrate . The concentration of the oxygen was increased from low to a higher concentration, this resulted in a ‘graded coating’ . A propanol plasma pretreatment (pretreatment) was employed to alter the properties of the graded coating.…”