The novel method we developed for understanding energy exchanges between argon (Ar) carrier gas and precursor molecules in a large-area (216 cm) dielectric barrier discharge (DBD) reactor has resulted in a series of articles, each relating to a different family of organic compounds. This communication focuses on two new groups, perfluorocarbons, (), and perchlorocarbons, , and compares results with earlier ones for hydrocarbons, ()[1] and hydrofluoromethanes, ()[2].
The precursors (in parts per thousand concentrations) were mixed with Ar in a 20 kHz, 8 kV (peak‐to‐peak) DBD. For each separate compound, the energy absorbed per molecule (, in eV), was determined from measurements of the time resolved discharge current, , and the gap voltage, . Plotting as a function of precursor flow rate, , and also , allows for the identification of the maxima, , identifying the boundary between the so-called “monomer-lean” and “monomer-rich” operating regimes. It has been highly instructive to plot x values as a function of atomization enthalpy () or alternatively molar mass (MM): in the case of saturated hydrocarbons, for example, this results in straight-line plots with rising MM or , while the trend was not as clear cut for halocarbons.
The process generally led to thin “plasma polymer” (PP) deposits (e.g. on Si wafer substrates). Their characteristics, like their or composition ratios from XPS measurements, strongly correlated with and , as did PP deposition rates and water contact angles.
[1] B. Nisol et al., Plasma Process Polym, 2016;14:e201600191.
[2] S. Watson et al., Plasma Process Polym, 2020;17:e201900125.
