In the current study, plasma-polymerized methyl methacrylate (PP-MMA) generation on the inner surface of a silicone tube was performed in a capacitively coupled discharge reactor. The possibility of generating plasma inside the tube was analyzed and calculated by using optical emission spectroscopy (OES). A hollow cathode model was first proposed to determine whether plasma discharge would be generated inside the tube in the low-pressure regime. Since the ignition of plasma inside the tube is necessary for the initiation of polymerization processes, the sheath thickness was calculated analytically. To achieve the goal, the electron temperature and density of plasma should be determined beforehand. In this study, the electron temperature and plasma density were measured and calculated according to OES spectra using both the modified Boltzmann plot and the line-ratio method. The results reveal that the occurrence of plasma inside the tube can be achieved if the tube’s inner diameter is greater than two times the thickness of the sheath. The effect of methyl methacrylate (MMA) monomer concentration on sheath thickness, and, hence, plasma generation and deposition, was investigated in the presence of argon plasma and MMA monomer. According to the study, one could control the ignition of plasma discharges inside the tube followed by plasma polymerization deposition. The OES method was also applied to identify the presence of the excited species related to the fragmented monomer. The deposition of PP-MMA films on the inner surface of the tube was confirmed via attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy.

A plasma system attached with one internal coil (for generating inductively coupled plasma) and two sputtering carbon targets was set up to deposit PP-MMA (plasma polymerized methyl methacrylate) thin films. PP-MMA was used as a model material in the present study. In the experiment, the working pressure and Ar/MMA flow ratio were varied, which resulted in the change in plasma conditions as well as the deposition rates. The optical emission spectroscopy (OES) method was applied to identify the presence of the excited species related to the fragmented monomer. In addition, the electron temperature and electron density were determined using the modified Boltzmann plot and line-ratio method, according to the measured OES spectra. The deposition rate of the PMMA film was then correlated with the determined plasma characteristics. To determine the vibrational modes of the deposited PP-MMA films, Fourier transformed infrared spectrometry (FTIR) was used. The highest deposition rate of PP-MMA could be obtained with the optimized working pressure and Ar/MMA volume ratio. This could be related to the plasma characteristics that contribute to the fragmentation of the monomer in the plasma.

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