Radiofrequency Plasma Polymers Containing Ionic Phosphonate Groups: Effect of Monomer Structure and Carrier Gas on Properties and Deposition Rate

Abstract

Radiofrequency (RF) plasma polymers prepared from perfluoroallylphosphonic acid (PAPA) are hydrophilic and have ionic properties. Unfortunately, deposition rates are low. The current study focuses on RF plasma polymers prepared from PAPA and pentafluoroallyldiethylphosphonate (PADP) with and without argon carrier gas. Plasma polymerized PADP films were similar in composition, structure, and properties to plasma polymerized PAPA films, but were deposited at much higher rates. The addition of argon to the PAPA discharges resulted in a decrease in mean deposition rate from 41.7 Å/min to less than 20 Å/min, while the deposition rate of plasma polymerized PADP increased significantly with the addition of argon to the discharge. PADP derived plasma polymer deposition rates ranged from 136 Å/min to 390 Å/min, depending on position in the reactor and presence or absence of argon carrier gas. PAPA-derived plasma polymers exhibited deposition rates and properties that were uniform throughout the reactor, while PADP-derived plasma polymers had maximum deposition under the upstream induction coil and linearly decreasing deposition rate with downstream distance in the reactor. Additionally, the PADP-derived plasma polymers exhibited downstream changes in atomic composition, structure, and physical properties, such as wettability and hardness. These changes were attributed to a “getter” effect upstream in the reactor in which ablated hydrogen species scavenge etching fluorine species in the plasma phase.