Surface Characterisation of Atmospheric Pressure Plasma-Modified and -Coated Polymers

Abstract

Atmospheric pressure plasma liquid deposition- APPLD, combines atmospheric pressure plasma with injection of atomised liquid from the delivery nozzle directly into the plasma. As such, the liquid within each droplet is protected from the plasma, and is carried intact to the surface, where it spreads and polymerises to form a conformal, high-value functional coating, which retains the properties of the original precursor molecule. The relationship between the chemistry of surfaces modified or deposited using this technique and the plasma deposition parameters has been investigated using a complementary suite of surface analytical techniques: contact angle analysis, X-ray photoelectron spectroscopy and atomic force microscopy. It has been shown that atmospheric pressure plasma (APP) can lead to the same level of oxidation as corona discharge. The APP has been shown to be less damaging to the substrate, and leads to a reduction in the formation of low molecular weight oxidised materials, despite the use of higher energy densities. A new methodology for curve-fitting of the XPS Si 2p and C 1s core levels of siloxane materials has been developed using siloxane standards. This method has been expanded to be used on siloxane coatings thinner than the depth of analysis of XPS. This enabled the chemistry of the coatings to be determined without the influence of the substrate. The chemistry of siloxane coatings deposited on poly(ethylene terephthalate) film have been related to the plasma parameters utilised during deposition. Up to 95% polymeric siloxane [(CH3)3SiO1/2 and (CH3)2SiO2/2] have been retained for deposition of poly(dimethylsiloxane) precursor. The use of a poly(hydrogenmethylsiloxane) precursor led to a more oxidised coating, with up to 25% siloxane in (CH3)SiO3/2 environment. The trends in deposition rate for PDMS and PHMS were also found to be different. Siloxane coatings durable to immersion in boiling water for 30 minutes have been achieved by plasma treatment of the substrate prior to deposition, and by plasma treatment of the coating following deposition. It is believed that improved grafting and enhanced crosslinking, respectively are the mechanisms behind this performance improvement