Energy of Reactions in Atmospheric‐Pressure Plasma Polymerization with Inert Carrier Gas

Abstract

A large reactor for performing dielectric barrier discharges (DBD) experiments at atmospheric pressure (AP) has been built and tested. The area of electrodes is more than 40 times greater than that of a small DBD cell, in which we have perfected a method formeasuring E g , the energy dissipated per cycle of the applied a.c. high voltage, V a (f). This methodology has been successfully applied to plasma polymerization experiments on the larger system, using volatile organic precursors (dopants) at ‰ concentrations in 10 standard liters per minute of argon (Ar). We measured DE g , the energy difference with and without dopant, for V a (f) $ 3 kV rms (20 f 40 kHz). From DE g we then derived E tot /N, the energy per molecule, and observed surprisingly good agreement with data published in the literature relating to lowpressure (LP) plasmas.

Energetics of Reactions in a Dielectric Barrier Discharge with Argon Carrier Gas: III Esters

“…We showed that this can lead to a multifold overestimate of W / FM , hence to erroneous conclusions . Accurate determination of energy absorbed by reagent (monomer) molecules was not accomplished until recent work in this laboratory, but the method for determining Δ E g and E m that we have developed now avoids pitfalls (i) and (ii) above . Clearly, E m (energy absorbed from the AP plasma per monomer molecule, in units of eV) is broadly equivalent to the Yasuda/Hegemann parameters; numerical results that we have presented give good reason for confidence, and the method appears to constitute a breakthrough …”

“…The DBD plasma reactor and its ancillary systems were described in detail in previous publications, so this needs no repetition here. Briefly, the top and bottom dielectrics, separated by a 2 mm gap, were Macor ® ceramic (3.50 ± 0.05 mm thick) and glass (3.00 ± 0.02 mm) plates, respectively.…”

“…This entails at least two difficulties: (i) accurate power measurements in DBD plasmas are error‐prone; (ii) even if W is determined with care, it includes both the carrier gas and the monomer. We showed that this can lead to a multifold overestimate of W / FM , hence to erroneous conclusions . Accurate determination of energy absorbed by reagent (monomer) molecules was not accomplished until recent work in this laboratory, but the method for determining Δ E g and E m that we have developed now avoids pitfalls (i) and (ii) above .…”

“…In a series of earlier studies, we already underlined the fact that PP literature has long been interested in correlating deposition kinetics, physico‐chemical and structural properties of deposited films, with energy transferred to the monomer molecules. For example, Hegemann and coworkers, developed a macroscopic phenomenology of PP based on the parameter W / F ( W being power input, and F the monomer flow rate), proportional to average energy transfer per monomer molecule during its travel through the active plasma zone, where W / F governs the formation of reactive film‐forming intermediates.…”

“…In preceding articles, we reported that several groups attempted to apply the W / FM concept to AP PP, using values of W determined from Lissajous figures or related techniques . This entails at least two difficulties: (i) accurate power measurements in DBD plasmas are error‐prone; (ii) even if W is determined with care, it includes both the carrier gas and the monomer.…”