Downstream Monomer Capture and Polymerization during Vapor Phase Fabrication of Porous Membranes

Enhancing the Kinetics of Vapor-based Polymerization by Pulsed Filament Approach

Initiated chemical vapor deposition is a versatile technique for synthesizing conformal polymer films on both planar and porous surfaces. It can retain functional groups and avoid undesired cross-linking. However, there is still room for enhancing its performance without altering the feed parameters. Here, we investigate a pulsed iCVD approach to improve the deposition process, achieved by switching on and off the resistively heated filament periodically. By strategically switching off the filament, a shortage of thermally activated primary radicals was created, which allowed uninterrupted chain propagation with fewer termination reactions and potentially increased monomer conversion rates. This has caused significantly faster deposition kinetics with a higher molecular weight and longer chain length for poly(glycidyl methacrylate) compared to continuous deposition. Spectra analyses confirmed that the functionality and stoichiometry ratios remained intact throughout the pulsed deposition process. The pulsed iCVD method is therefore a competitive and sustainable tool, demonstrating fast deposition kinetics and a well-preserved functionality.

Influence of Oblique Angle Deposition on Porous Polymer Film Formation

In this study, we applied oblique angle deposition to a modified initiated chemical vapor deposition (iCVD) process to synthesize porous poly(methacrylic acid) (PMAA) films. During the modified iCVD process, frozen monomer molecules are first captured on a cooled substrate, then polymerization occurs via a free radical polymerization mechanism, and finally, the excess monomer is sublimated, resulting in a porous polymer film. We found that delivering the monomer through an extension at an oblique angle resulted in porous films with three morphological regions. Region 1 is located nearest to the monomer extension outlet and consists of porous polymer pillars; region 2 consists of densified pillars, which occur due to the recapturing and polymerization of the sublimated monomer; and region 3 is located furthest from the monomer extension outlet and consists of dendritic structures, which occur due to low monomer concentration. We investigated the role of substrate temperature and monomer deposition time on the growth process. We found that changing the extension angle influenced the location of the regions and the film coverage across the substrate. Our results provide useful guidelines for tuning the structures within porous polymer films by varying the angle of monomer delivery.