Energy conversion efficiency in low- and atmospheric-pressure plasma polymerization processes with hydrocarbons

Area of Science:

• Plasma Science and Engineering
• Polymer Chemistry
• Surface Science

Background:

• Correlating plasma polymer (PP) structure with deposition parameters, especially energy input per monomer molecule (Em), is a long-standing challenge.
• Established methods exist for measuring Em or apparent activation energy (Ea) in low-pressure (LP) and atmospheric-pressure (AP) electrical discharge plasmas.

Purpose of the Study:

• To investigate the relationship between energy input and reaction mechanisms in plasma polymerization of small hydrocarbons.
• To validate a new parameter, energy conversion efficiency (ECE), for comparing LP and AP plasma experiments.
• To identify critical energy thresholds that define different reaction pathways.

Main Methods:

• Measurement of energy input per monomer molecule (Em) and apparent activation energy (Ea) in LP and AP plasmas.
• Utilized a novel energy conversion efficiency (ECE) parameter for direct comparison of different plasma conditions.
• Studied small hydrocarbon monomers: acetylene, ethylene, and methane.

Main Results:

• Identified "critical" Em (or Ea) values that effectively demarcate distinct energy conversion efficiency (ECE) regimes.
• Demonstrated remarkable agreement between critical energy values across LP and AP plasma experiments.
• Correlated these critical energy values with specific reaction mechanisms, including dissociation, recombination, gas-phase oligomerization, and surface processes.

Conclusions:

• The energy conversion efficiency (ECE) parameter provides a unified framework for comparing plasma polymerization across different pressure regimes.
• Critical energy input values serve as reliable indicators of underlying reaction mechanisms in plasma polymer formation.
• This work offers a deeper mechanistic understanding of plasma polymerization for small hydrocarbons, crucial for tailoring PP coatings.