Differences in the Aging of Allyl Alcohol, Acrylic Acid, Allylamine, and Octa-1,7-diene Plasma Polymers As Studied by X-ray Photoelectron Spectroscopy

Thin organic films were deposited from plasmas of allyl alcohol, acrylic acid, allylamine, and octa-1,7-diene onto aluminum substrates. These plasma polymerized films were analyzed by X-ray photoelectron spectroscopy (XPS) before and after prolonged periods of storage under laboratory atmosphere to attempt to quantify changes in surface chemistry as a result of aging over 400 days. Plasma polymers produced from octa-1,7-diene and allylamine showed a distinct uptake of oxygen during the first 30 days post-polymerization, gradually leveling off but not appearing to reach a stable level. In addition, the allylamine plasma polymers showed a loss of nitrogen. Those polymers produced from allyl alcohol and acrylic acid plasmas did not show any changes with time in their oxygen content, or in the composition of their C 1s core levels. While the aging seen in the hydrocarbon plasma polymer and the nitrogen-containing plasma polymer is broadly consistent with what has been previously reported in the literature for similar materials, the aging of plasma-polymerized allyl alcohol and acrylic acid is quite different. The data highlight the differences in aging between different monomers plasma polymerized under the same reactor conditions, and “alike” plasma polymers deposited using very different experimental setups (reactor geometry, power coupling, and frequency).