Double tube configuration of atmospheric pressure plasma jet for deposition of organic coatings in open air

A double coaxial tube configuration of atmospheric pressure plasma jet (APPJ) was compared with a single tube one for open air plasma polymerization. The effectiveness on minimizing the influence of ambient air during the deposition process was shown for a double tube APPJ i.e. Ar gas fed into the outer glass tube acted as a shielding gas. The inner tube, acted as the powered electrode was fed with a mixture of Ar gas with the precursor, i.e., toluene vapor, a non-oxygen containing precursor. The dynamics of gas flow and its dependence on composition was investigated with a Schlieren imaging system. Coatings obtained with both configurations were analyzed by fourier transform infra-red (FTIR) and x-ray photoelectron spectroscopy (XPS). The results show clearly that the argon shielding gas largely protects the diffusion of oxygen in the deposition zone, giving rise to polymers with much less oxygen incorporated in their structure, and a good retention of the aromatic rings of toluene. Furthermore, the area of the treated zone and the chemical composition of the coating deposited is highly localized (1 mm) in the double tube giving dense stable carbon films while the deposition in the single tube much bigger (6 mm), and the deposited coatings are unstable and easily washed away. Hence, the results obtained with this innovative system provide a new path in plasma polymerization and continuous treatments of large surfaces, with improved coating stability and chemical retention.