Deposition of polymethyl methacrylate on polypropylene substrates using an atmospheric pressure dielectric barrier discharge

In this work, an atmospheric pressure glow-like dielectric barrier discharge in helium with small admixtures of methyl methacrylate (MMA) is used for the deposition of thin polymethyl methacrylate (PMMA) films. The effect of discharge power and feed composition (monomer concentration) on film properties has been investigated by means of Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results are described by defining a W/FM value, where W is the discharge power, F the monomer flow rate and M is the molecular weight of the monomer. It is shown in this paper, that the deposition rate and the chemical composition of the deposited film change with varying W/FM values. At low W/FM values, high deposition rates of up to 2 nm/s are observed and the plasma-polymerized MMA chemically resembles the conventionally synthesized PMMA. In contrast, using high W/FM values (≥102 MJ/kg) leads to lower deposition rates (as low as 0.9 nm/s), while the plasma-polymerized MMA films contain less ester groups and a larger amount of ether and/or alcohol groups. One should therefore carefully choose the deposition parameters in order to obtain a high deposition rate and a high retention of ester groups in the plasma-polymerized MMA films.