The Role of Ions in the Plasma Polymerization of Allylamine

Abstract

The radio-frequency-induced plasma polymerization of allylamine has been investigated in the plasma-gas phase by mass spectrometry and at the plasma−solid interface by means of an ion flux probe and a quartz mass balance. The surface chemistry of the deposits has been determined by X-ray photoelectron spectroscopy. The objective of this study was to unravel the mechanism(s) by which allylamine plasma polymers form. The results are compared with those obtained in an earlier investigation of the plasma polymerization of acrylic acid. In the plasma-gas phase, evidence is provided for reactions between cations and intact neutral monomers (allylamine). These oligomerization reactions were found to be relatively power-insensitive compared with those seen in plasmas of acrylic acid, as was the gas-phase concentration of the intact neutral monomer. At the polymer surface, ion fluxes were found to increase with plasma input power (P) from 6.6 × 1016 ions m-2 s-1 at 1 W to 1.4 × 1018 ions m-2 s-1 at 14 W. The ionic mass transport to the polymer surface (ion mass flux) was calculated by multiplying the measured ion flux by the average ion mass (determined by mass spectrometry). At P = 1 W, the ion mass flux was 11.7 μm m-2 s-1, and at 14 W, the ion mass flux was 226.6 μm m-2 s-1. These values differed from the total mass deposition rates measured by the quartz mass balance, which were 18.7 and 127.1 μm m-2 s-1, respectively. However, the relationship found between the ion mass flux, the mass deposition rate, and P was complex, and it is shown that, at very low P (<1 W), the ion mass flux is sufficient to account for all of the deposit.

On the importance of ions and ion-molecule reactions to plasma-surface interface reactions

“…The present results indicate plasma conditions that could emphasize such molecular ions, which, as noted above, may be useful for identifying key ionized species diffusing to the substrate as well as mechanisms for ionization in the plasma. Indeed, it has recently been proposed that ion-molecule reactions in some plasma systems are vital for producing species that are critical to formation of particular film chemistries [10,11,53]. Specifically, Shamamian et al have found that an ion-molecule protonation reaction in isopropyl alcohol plasmas leads to formation of the fragment CH 3 CHCH 3 ϩ (m/z ϭ 43), whereas a direct electron dissociation-ionization reaction yields the CH 3 CHOH ϩ fragment ion (m/z ϭ 45) [11].…”

“…In many plasma polymerization systems, ion-molecule reactions clearly lead to formation of oligomeric species [10,11]. Ion-molecule reactions can often lead to different product branching ratios than those produced via electron impact reactions.…”

Switchable coatings for biomedical applications

“…15 Plasma polymers have found many material and biomaterial applications owing to their ability to provide films with complete surface coverage (pinhole free), low roughness and controlled concentrations of functional groups. 15,16 Plasma polymerisation also has the advantage of being a sterile solvent-free technique. 4,16 Films of amine plasma polymers such as allylamine plasma polymers (ALAPP) are of significant value as coatings for biomedical devices due to the ease of subsequent modification.…”

“…15,16 Plasma polymerisation also has the advantage of being a sterile solvent-free technique. 4,16 Films of amine plasma polymers such as allylamine plasma polymers (ALAPP) are of significant value as coatings for biomedical devices due to the ease of subsequent modification. Studies into allylamine plasma polymers have found that allylamine is not as sensitive as other monomers towards fragmentation in the plasma, producing films with a high retention of the amine functionality within the deposited film.…”

“…Studies into allylamine plasma polymers have found that allylamine is not as sensitive as other monomers towards fragmentation in the plasma, producing films with a high retention of the amine functionality within the deposited film. 16,17 Biochips containing protein, DNA or cell microarrays are exemplary applications that require spatially controlled attachment of biomolecules. This is currently, achieved using patterning of surface chemistry or robotic spotting methods.…”