Energy Conversion Efficiency in Plasma Polymerization - A Comparison of Low- and Atmospheric-Pressure Processes

In the plasma polymerization literature, there has been an interest since at least the 1970s to correlate the structure of plasma polymer (PP) deposits with plasma parameters during deposition, most particularly with the energy input per monomer molecule, (E)m. In our two laboratories, we have developed methods for measuring E-m (or somewhat equivalent, E-a) in low- (LP) and atmospheric-pressure (AP) discharge plasmas. In this article we propose a new parameter, the so-called energy conversion efficiency, ECE, which permits direct comparison of LP and AP experiments. This is done for the case of three model monomer compounds, ethane, acetylene, and acrylic acid (AAc). "Critical'' energy values that demarcate ECE regimes separating different fragmentation/reaction mechanisms agree remarkably well for all three monomers examined; resulting E-m (or E-a) values are correlated with specific mechanisms, and the numerical results are convincingly supported by data from the chemical literature.