Reaction of CO sub(2) Gas with (radicals in) Plasma-Polymerized Acrylic Acid (and Formation of COOH-Rich Polymer Layers)

In contrast to most of the existing literature on plasma polymerization of acrylic acid (AA), not only the chemical structure and film thickness of the deposits were studied, but also a new way to obtain COOH-rich surfaces were studied. This is an important aspect when applying the obtained coatings for biomedical and electronics applications. Therefore, acrylic acid/CO sub(2) polymer films with a thickness of ca. 150nm were deposited in the pulsed plasma regime onto polyethylene and aluminum. Their structure-property relationships were studied in dependence on the mixture ratio of acrylic acid monomer and CO sub(2) gas. The influence of the CO sub(2) gas on the regularity and functionality of plasma-deposited poly(acrylic acid) (PAA) was studied in detail using bulk-sensitive (FTIR) as well as surface-sensitive methods, such as X-ray photoelectron spectroscopy. Results obtained show, in presence of a small amount of CO sub(2) gas within the acrylic acid plasma, a structure of PAA with high concentration of COOH groups was estimated. A polymer network is obtained with an increasing abundance of branched groups for AA/CO sub(2) with increasing CO sub(2) gas in the mixture. A little amount of CO2 gas with acrylic acid monomer during plasma leads to a structure of poly(acrylic acid) with higher concentration of COOH groups than that for pure acrylic acid. However, energy input in its different forms damages poly(acrylic acid) at larger distance from a layer to layer which is already polymerized in addition to fragmentation and poly-recombination in presence of more than 60 % of CO sub(2) gas in the chamber.