Table 4.

Bridging the gaseous reactive species from plasma with the functional groups introduced on polymer surfaces.

Gaseous Reactive Species	Gas/Vapor Sources	Functional Groups Introduced on Polymer Surface	Effects & Applications
Oxygen radicals	O2, water vapor	-Carbonyl groups (C=O) -Carboxyl groups (-COOH) -Hydroxyl groups (-OH) [210]	Increase in the polymer surface energy that can then improve wettability, adhesion and compatibility with other materials [211].
Excited water species	Water vapor	-Hydroxyl groups (-OH)	Improving the wettability and adhesion of the polymer [212,213].
Nitrogen radicals	N2, ammonia (NH3)	-Amine groups (-NH2) -Amide groups (-CONH2) -Nitrile groups (-CN) [214,215]	Improving cell adhesion of PLA samples, as evidenced by MTT and SEM [216]. Enhancing reactivity and hydrogen bonding capabilities of polymer surfaces.
Nitric oxide radicals	NO, NO2	-Nitro groups (-NO2) -Nitrite groups (-ONO) -Amine groups (-NH2) -Amide groups (-CONH2)	Polymer surfaces with antibacterial properties for biomedical applications [217,218].
Hydrogen radicals	H2	Hydrogen-containing functional groups that are both stable and unreactive.	Plasmas can effectively clean surface contaminants (e.g., residual monomers, surfactants) from polyethylene, polypropylene and polyimide [219,220].
Carbon radicals	CH4, C2H6	-Methyl groups -Ethyl groups -Etc. [221,222].	The functional groups can modify the surface properties of the polymer, such as its hydrophobicity or conductivity [223].
Reactive oganic species	Styrene, vinyltrimethylsilane (VTMS) or divinylbenzene (DVB)	Vinyl groups (-CH=CH2)	Introducing unsaturation into a surface to make it more reactive and capable of undergoing further polymerization or crosslinking.
Fluoro (carbon) radicals	SF6, CF4 or fluorocarbon precursors.	Fluorine-containing groups (-CFX)	Enhancing hydrophobicity, chemical resistance and non-stick properties.