Critical evaluation of conditions of plasma polymerization

TLDR

Plasma polymerization occurs in a reactive, self‑exhausting gas phase, so parameters measured before discharge, such as pressure and monomer flow, are not applicable to the steady‑state plasma conditions. The study examines the true significance of experimental parameters relevant to plasma polymerization. Comparisons of different organic compounds should be made at equivalent composite discharge power levels defined by W/FM, where W is discharge power, F is monomer flow rate in moles, and M is monomer molecular weight. Deposition‑rate data measured at fixed flow or power, or their dependence on these variables, fail to provide meaningful comparisons of the characteristic behavior of organic compounds in plasma polymerization.

Abstract

Abstract Under conditions of plasma polymerization, we are dealing with the “reactive” or “self‐exhausting” rather than the “nonreactive” or “non‐self‐exhausting” gas phase (plasma). Therefore, many parameters that define the gas phase, such as system pressure and monomer flow rate, which are measured in the nonplasma state (before glow discharge is initiated), do not apply to a steady state of plasma, the conditions under which most of the studies on plasma polymerization are carried out. Consequently, information based on: (1) the polymer deposition rate measured at a fixed flow rate and discharge power, (2) the dependence of deposition rate on flow rate at fixed discharge power, or (3) the dependence of deposition rate on discharge power at fixed flow rate, does not provide meaningful data that can be used to compare the characteristic nature of various organic compounds in plasma polymerization. The significance and true meaning of experimental parameters applicable to conditions of plasma polymerization are discussed. The most important feature is that plasma polymerizations of various organic compounds should be compared at comparable levels of composite discharge power parameter W/FM , where W is discharge power, F is the monomer flow rate (given in moles), and M is the molecular weight of a monomer.