A Comparison between Gas and Atomized Liquid Precursor States in the Deposition of Functional Coatings by Pin Corona Plasma

This work directly compares vapour and liquid aerosol states for the deposition of perfluorocarbon coatings using an atmospheric pressure, non-thermal equilibrium plasma jet system. The objective of the study is to evaluate how the physical state of the precursor (gas or liquid), influences the fragmentation of the monomer molecules in the plasma and the subsequent coating properties. Specifically the effect of gas or liquid aerosol precursor feed on the ability to achieve a soft plasma polymerization (SPP) is assessed with a view to producing a coating that exhibits minimal fragmentation, while being well cross-linked. The precursor (perfluoro-1-decene) was introduced into a helium plasma and coatings deposited at rates of up to 50 nm . min(-1). The deposited coatings were examined using XPS, FTIR, contact angle and ellipsometric measurements. These indicated that a controlled polymerization reaction through the vinyl group of the monomer had taken place in the case of the gas deposited samples with only minor fragmentation of the functional perfluoro chain. Furthermore, a high level of cross-linking was achieved and the perfluorocarbon coatings were stable to a toluene wash. In contrast, while coatings deposited using the liquid deposition technique showed good retention of monomer molecular structure, they exhibited poor stability when immersed in toluene. This is attributed to lower levels of cross-linking of the liquid precursor in the plasma, compared with coatings deposited using the gaseous precursor technique.