Non-line-of-sight synthesis and characterization of a conformal submicron-thick cationic polymer deposited on 2D and 3D substrates

Abstract

The non-line-of-sight nature of initiated chemical vapor deposition (iCVD) makes it an amenable technique for depositing thin, conformal polymer films on three-dimensional (3D) high surface-area substrates. Adding to the versatility of iCVD, we process the deposited film in situ to impart additional functionality. Herein we describe fabricating submicron-thick positively charged polymer films with labile anions, a class of materials that brings ion-transport regulation to water desalination, gas separations, and energy-storage systems. Coatings of iCVD-deposited poly(4-dimethylaminomethylstyrene) (pDMAMS) on planar and 3D substrates are reacted with an alkylating/cross-linking reagent to yield quaternary ammonium-containing pDMAMS⁺. By optimizing deposition conditions, we demonstrate conformal coatings of pDMAMS and pDMAMS⁺ spanning a thickness range of 30–1000+ nm. Chemical and mechanical characterization confirms the successful quaternization of the iCVD-generated films, subsequent ion exchange of various counterions (Br⁻, HCO₃⁻, and OH⁻), and enhanced modulus of the crosslinked pDMAMS⁺ polymer. The use of grazing-incidence X-ray scattering reveals the films are noncrystalline and contain ion clusters with anion-dependent geometry. By understanding the impact of deposition conditions and functionalization on subsequent physicochemical-mechanical properties, we lay the groundwork for using iCVD-derived pDMAMS⁺ films in targeted applications.