Influence of the pressure on the interaction between stearic acid and Ar-O2 in inductively coupled radio frequency plasma

Abstract

This work aimed to analyze the influence of treatment pressure on the interaction between stearic acid and an Argon-Oxygen plasma. The fixed variables were the applied RF plasma power (50 W), treatment time (30 min), and treatment starting temperature (273 K). The pressure was varied as follows: 0.2, 0.6, and 1.0 Torr. For all treatment conditions, the etching of the samples was observed, as evidenced by the mass loss of the specimens and by following the gaseous by-products of reactions employing a mass spectrometer coupled to the reaction chamber. Optical emission spectroscopy followed the emission lines of oxygen active species. Functionalization of the specimens was also observed, as shown by the results obtained by Fourier-transform infrared spectroscopy (FTIR) and through XRD analysis. A liquid phase was formed for samples treated at 0.6 and 1.0 Torr, which favored the functionalization process and broadened the band present in the region from 1750 to 1700 cm -1 , resulting in amorphous phases. An increase in the intensity of the characteristic peaks of esters was also observed. It can be concluded that the higher pressure favors the formation of a liquid phase and reaction kinetics, resulting in higher functionalization and lower etching.