Influence of Oblique Angle Deposition on Porous Polymer Film Formation

Abstract

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.

Designing Organic and Hybrid Surfaces and Devices with Initiated Chemical Vapor Deposition (iCVD)

“…Reproduced with permission. [ 141 ] Copyright 2023, American Chemical Society. D) the monomer and porogen phase separated, while nanoscale porosity resulted using E) a miscible porogen (Section 14.3), Reproduced under the terms of the CC‐BY 4.0 License.…”

“…Localized growth of porous polymers was demonstrated by combining oblique angle deposition with the use of excess monomer as the porogen. [ 141 ] The angled extension tube added to the iCVD reactor caused the inlet monomer vapor to impinge on the growth surface at an oblique angle (Figure 15B,C). The concentration gradient of monomer vapor around the impingement point creates localized deposition with three distinct morphological regions.…”

“…Copyright 2021, American Chemical Society. Reproduced with permission [141]. Copyright 2023, American Chemical Society.…”

Vapor Phase Deposition of Porous Polymer Dendrites

“…21 We recently applied the concept of oblique angle deposition to our modified iCVD process by adding an extension to deliver the monomer at an angle to the substrate which resulted in porous polymer coatings with distinct morphological regions. 27 The film closest to the monomer extension outlet consisted of porous pillar-like structures resembling those grown in the absence of the extension, and dendritic structures were formed furthest away from the extension as a result of low monomer concentration. In this work, we further investigate the formation of these dendritic structures by limiting the monomer concentration across the entire reactor and studying the shape of the structures formed at physical defects such as scratches.…”