Modification of stearic acid in ar and Ar-O 2 pulsed DC discharge

Abstract

Stearic acid (CH 3(CH 2) 16COOH) was treated with Ar and Ar-O 2 (10%) pulsed DC discharges created by a cathode-anode confined system to elucidate the role of oxygen in plasma cleaning. The treatment time (5 to 120 minutes) and plasma gas mixture (Ar and Ar-O 2) were varied, and the results showed that the mass variation of stearic acid after Ar-O 2 plasma exposure was greater than that of pure Ar plasma treatment. Thus, compared to Ar *, active oxygen species (O and O 2, in all states) enhance the etching process, regardless of their concentration. During the treatments, a liquid phase developed at the melting temperature of stearic acid, and differential thermal analyses showed that the formation of a liquid phase was associated with the breakage of bonds due to treatment with an Ar or Ar-O 2 plasma. After treatment with Ar and Ar-O 2 plasmas, the sample surface was significantly modified, especially when Ar-O 2 was utilized. The role of oxygen in the treatment process is to break carbonaceous chains by forming oxidized products and/or to act as a barrier again ramification, which accelerates the etching of stearic acid.