Several reaction mechanisms have been proposed for the formation of plasma polymers, such as monomer fragmentation followed by poly‐recombination into randomly structured and crosslinked films; fragmentation, accompanied by the formation of acetylene or other film‐forming intermediates and deposition of polystyrene‐like material; plasma‐initiation of a radical chain‐growth polymerization; and ion‐molecule reactions, as well as ionic chain‐growth polymerization. The bulk structure of plasma polymers is completely irregular, far from that of conventional polymers. The retention of functional groups during plasma polymerization tends to be greater than that of the entire monomer structure found again as an intact repeat unit in the resulting plasma polymer. An alternative method for depositing ultra‐thin, pin‐hole free coatings, ones that possess regular structures, is by electrospray ionization (ESI) of pre‐fabricated polymers.

Poly(acrylic acid) films with a thickness of about 150 nm were deposited using a pulsed plasma onto aluminum and glass. The structure/property relationships of these samples were studied in dependence to the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time, volume sensitive methods (FTIR, dielectric spectroscopy, and differential scanning calorimetry) are combined with surface analyses i.e. XPS. For an unambiguous identification of COOH groups by XPS, derivatization with trifluoroethanol was accomplished. Quantitative FTIR investigations give qualitatively a dependence of the concentration of COOH groups upon DC similar to that given by XPS investigations. The observed differences are discussed considering the different analytical depths of both methods. The dielectric measurements reveal that the structure of the plasma deposited films is different from that of the bulk material. Moreover, these measurements show also that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating, where the reaction kinetics depends on DC.

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The production of chemically‐defined plasma polymers and the introduction of monotype functional groups onto polymer surfaces are described. One method is to lower the energetic level of low‐pressure plasmas. Pressure‐ and plasma‐pulsed plasmas were successfully tested for the production of chemically‐defined plasma polymers by increasing the monomer supply during the plasma‐off period. Well‐defined ultra‐thin polymer films with regular structure were deposited from atmospheric plasmas by electrospray techniques. Post‐plasma wet‐chemical processing was also applied, as were gas/liquid‐based aerosols and underwater plasmas.magnified image

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