Surface Functionalization of Additively Manufactured Polypropylene and Stainless Steel 316L: Impact on Wettability and Oxygen Nucleation

Bubble nucleation, a fundamental solid–gas interaction, plays a critical role in both natural phenomena and industrial processes. In water electrolysis, it is relevant not only for the generation of H2 bubbles but also for the formation of O2 as a byproduct, which significantly impacts heat and mass transfer efficiency. While surface functionalization for bubble management has been actively explored for electrodes, the electrolyzer periphery has received little attention to date. Additive manufacturing enables the design of advanced geometries to optimize the multiphase flow in such systems. In this study, the wettability of additively manufactured polypropylene and stainless steel 316L substrates is modified by plasma-enhanced chemical vapor deposition based on 1H,1H,2H,2H-perfluorooctyl acrylate (PFAC-6) and hexamethyldisiloxane (HMDSO), creating hydrophobic or hydrophilic surfaces with final water contact angles ranging from 40 to 145°. Surface morphology and properties are assessed by digital microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy. The coating stability and long-term wettability in contact with air or water, as a first step toward industrial conditions, were monitored over a period of up to 150 days. X-ray photoelectron spectroscopy identified distinct aging mechanisms: defluorination for PFAC-6 coatings and reorientation of polar surface groups for HMDSO. Bubble dynamics in O2-oversaturated solutions are recorded and analyzed using machine learning techniques, showing O2 bubble coverage increased by up to 500% for polypropylene and 350% for stainless steel with PFAC-6, while HMDSO coatings reduced nucleation down to 30%. This work highlights the pivotal role of surface structure and chemical modification in governing solid–gas interactions and offers valuable insights for the development of optimized materials in industrial applications such as electrolysis.