A direct comparison between gas state and atomised liquid state precursor in the deposition of functional coatings by pin corona plasma

Abstract

An atmospheric pressure non-thermal equilibrium pin corona plasma jet was used to deposit polymeric coatings from monomer precursor in both vapour and liquid aerosol states to allow a direct comparison of the quality and performance of the as-deposited coatings, specifically with respect to the achievement of soft plasma polymerisation (SPP) where the coating exhibits minimal fragmentation or damage to the monomer molecule while, at the same time, being highly cross-linked. A long chain perfluorocarbon molecule was introduced into the helium plasma and coatings deposited at rates of up to 50 nm/min. XPS, FTIR, contact angle and ellipsometric measurements indicated that a controlled polymerization reaction had taken place in the case of the vapour deposited samples through the vinyl group of the monomer, with only minor fragmentation of the functional perfluoro chain. Furthermore, a high level of cross-linking was achieved and the coatings were stable to a toluene wash. In contrast, while the liquid deposition samples showed good retention of monomer molecular structure, they exhibited negligible cross-linking and were readily removed by immersion in toluene rendering them functionally useless.

Water Sensitive Coatings Deposited by Aerosol Assisted Atmospheric Plasma Process: Tailoring the Hydrolysis Rate by the Precursor Chemistry

“…Thus, to overcome the fragmentation processes – or at least minimized their occurrence, during the last decade has been pointed out the possibility to improve the degree of retention of the precursor in specific conditions – namely soft plasma polymerization – by decreasing the energy delivered within the discharge per molecule . Different approaches have been proposed in the community to ensure the preservation of the functionality of the precursor such as working in pulsed mode, low power with plasmagen gases such as helium which required less energy to ignite compared to nitrogen, by acting on the injection of the precursor (aerosol or gaseous state), and more recently by using precursor bearing acrylate moieties . In fact the use of acrylates seems to be a promising way thanks to their high reactivity towards the plasma activation, requiring a very low power to polymerize within the plasma discharge and consequently allowing a high degree of the preservation of the precursor functionality to be reached.…”