Speaker
Description
The novel method we developed for understanding energy exchanges between argon (Ar) carrier gas and precursor molecules in a large-area (216 cm$^2$) 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, ($C_xF_y$), and perchlorocarbons, $(C_xCl_y)$, and compares results with earlier ones for hydrocarbons, ($C_xH_y$)[1] and hydrofluoromethanes, ($CH_xF_y$)[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 ($E_m$, in eV), was determined from measurements of the time resolved discharge current, $I_d$, and the gap voltage, $V_{gap}$. Plotting $E_m$ as a function of precursor flow rate, $F_d$, and also $1/F_d$, allows for the identification of the maxima, $(E_m)_{max}$, identifying the boundary between the so-called “monomer-lean” and “monomer-rich” operating regimes. It has been highly instructive to plot $(E_m)_{max}$x values as a function of atomization enthalpy ($H_f$) or alternatively molar mass (MM): in the case of saturated hydrocarbons, for example, this results in straight-line plots with rising MM or $H_f$, 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 $C/F$ or $C/Cl$ composition ratios from XPS measurements, strongly correlated with $E_m$ and $F_d$, 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.
