Rational approaches for optimizing chemical functionality of plasma polymers: A case study with ethyl trimethylacetate

Abstract

Improved retention of desirable chemical structures during plasma polymerization requires rational tailoring of plasma‐phase conditions. Using ethyl trimethylacetate, we studied the effects of pressure and power on the contribution of intact molecular ions to deposition and retention of ester groups. The abundance of protonated molecular ions in plasmas varies with pressure and power, but the functionality of plasma polymers, assessed by X‐ray photoelectron spectroscopy and time‐of‐flight secondary ion mass spectrometry, is not correlated. Together with high ion flux, the ion energy distribution was found to be a key parameter and needs to be tailored to enable the soft landing of ions on the surface after traversing the sheath. The compromise between the abundance of ions and their energy distribution is optimal near the transition between the α and γ plasma phases.

Plasma surface engineering for manmade soft materials: a review

“…Different strategies to obtain stable and functional PPFs have thus been explored including formation of a vertical gradient structure in the PPF during plasma deposition and chemical post-plasma treatments [195]. Recently, protonation of the starting molecules in the gas phase has been identified as an interesting approach to avoid strong fragmentation of monomers bearing functional groups at moderate SEI [196]. The examination of the fragmentation pathways of ethanol, C 2 H 5 OH, acetic acid, CH 3 COOH, and glucose, C 6 H 12 O 6 , in a plasma by ICP-MS revealed that protonated molecules are indeed more stable in the gas phase than the free molecules [197].…”

“…Protonated molecules can thus also be detected by mass spectrometry, that is, at a significant distance from the plasma. The H + -loaded molecular ions are accelerated in the plasma towards the substrate, where soft landing of protonated molecules retains their functionality [196]. This way, plasma polymer coatings were deposited from ethyl αbromoisobutyrate that retained α-bromoisobutyryl functional groups able to graft a dense layer of HEMA polymer brushes to allow for a soft material surface [198].…”

Plasma polymerization for biomedical applications: A review

“…This has been accompanied by much fundamental research on the physicochemical processes in plasma polymerization and their control and fine‐tuning, [ 2,3,11 ] on detailed characterization of the surface chemistries and properties of plasma polymers, [ 12,13 ] and on tailoring the surface chemistries and properties of plasma polymers including optimization of the surface density of specific functional groups such as amines, [ 14 ] carboxylic groups, [ 15–17 ] aldehyde, [ 18,19 ] and ester groups. [ 2,3,20–23 ] Volatile monomers bearing the functional group of interest are utilized (e.g., acrylic acid or oxazoline [ 24 ] to produce COOH groups or aliphatic amines for NH 2 groups), and low monomer fragmentation plasma conditions (e.g., low power, pulsed plasmas at a low duty cycle, reduced ion bombardment at the surface of the substrate, etc. ), for optimal retention of the structure of the monomer and incorporation of the functional group in the resulting coating.…”

“…The unique features of plasma polymers have led to extensive research on fundamental questions such as improved control of the bulk and surface chemistries, [2,3] and a wide range of applications-oriented research and development projects towards their utility for specific intended applications. A key premise has been the ability of plasma polymers to form uniform, well-adhering coatings on a wide range of substrate materials.…”

“…With the ever-increasing emphasis on advances in modern science and medicine for human health care, researchers and product developers have considered plasma polymers as components of advanced products for a wide range of potential applications. This has been accompanied by much fundamental research on the physicochemical processes in plasma polymerization and their control and fine-tuning, [2,3,11] on detailed characterization of the surface chemistries and properties of plasma polymers, [12,13] and on tailoring the surface chemistries and properties of plasma polymers including optimization of the surface density of specific functional groups such as amines, [14] carboxylic groups, [15][16][17] aldehyde, [18,19] and ester groups. [2,3,[20][21][22][23] Volatile monomers bearing the functional group of interest are utilized (e.g., acrylic acid or oxazoline [24] to produce COOH groups or aliphatic amines for NH 2 groups), and low monomer fragmentation plasma conditions (e.g., low power, pulsed plasmas at a low duty cycle, reduced ion bombardment at the surface of the substrate, etc.…”