Preparation of Stable Wetting Surface by Hyperthermal Hydrogen Induced Cross-Linking of Poly(acrylic acid) on Poly(chloro-p-xylylene) Film

Abstract

Enhancing surface wetting is very critical for various applications of polymer films. Although existing modification methods (e.g., UV radiation and plasma treatments) can improve the wetting of polymer films by inserting hydrophilic groups, the resultant polymer surface is unstable and shows strong hydrophobic recovery in a short time (less than 1 day) due to the rearrangement of the polymer chains. Herein, we report a new approach to prepare stable wetting surface by cross-linking hydrophilic poly(acrylic acid) (PAA) molecules on poly(chloro-pxylylene) (PPXC) films via hyperthermal hydrogen induced crosslinking (HHIC) treatment. With the HHIC treatment, the polar functionalities of PAA (e.g., −COOH) can be preserved through selective cleavage of C−H bonds and subsequent cross-linking of resulting carbon radicals generated on PAA and PPXC chains. HHIC-treated PAA−PPXC film shows an excellent wetting stability, of which WCA and surface energy stay almost the same over 40 days. The improved wetting stability of PPXC film is attributed to the controllable HHIC reaction without undesirable side reaction (e.g., the scission of polymer chain backbone), which effectively restricts the rearrangement of PAA chains on the surface. Besides, the improved wetting stability by our approach results in reliable adhesion between silver ink and polymer films. Thus, fixing hydrophilic molecules on hydrophobic polymer surface by HHIC treatment could be an alternative approach to conventional surface treatments for preparation of stable wetting surface on polymer films.

Polyacrylic acid ultra‐thin films: Influence of cross‐linking structure via hyperthermal hydrogen‐induced cross‐linking

“…Previous works have grafted PAA onto substrates using various methods. [12][13][14][15][16][17][18][19][20][21][22][23] However, the treatments adopted by most of these reports are not pollution-free. Moreover, pulse microwave plasma CVD, which has been widely employed to deposit PAA layer, [15][16][17][18] may lead to a low COOH group concentration when acrylic acid is used during deposition in the grafting.…”

“…Herein, we focused on the growth of ultra‐thin PAA layer on Si wafer by spin‐coating and the self‐crosslinking behavior of as‐prepared films by using HHIC method 21 . The H is cleaved not only from CH, but also from functional group COOH.…”

“…19 However, a complex focusing electron beam in a high vacuum system as a photo initiator for photo-induced cross-linking limits the cross-linking area due to a small electron beam size. Hyperthermal hydrogen-induced cross-linking (HHIC), a relatively new technology with several advantages such as low temperature treatment, both large area and local treatment, without requirement of crosslinking agent and without contamination, can cross-link PAA efficiently and firmly with the polymer substrates, such as PLA substrate, 20 PPXC substrate, 21 and hydrophobic polypropylene substrate. 22 Although previous studies focused on cross-linking PAA and polymer substrates, it's worth noting that HHIC can also cause PAA to cross-link by itself.…”

“…20,24 Herein, we focused on the growth of ultra-thin PAA layer on Si wafer by spin-coating and the self-crosslinking behavior of as-prepared films by using HHIC method. 21 The H is cleaved not only from C H, but also from functional group COOH. The self-cross-linking of PAA are then demonstrated by C C and the COOC bonding, which was evidenced by both XPS results and the water contact angle test.…”

Patternable Poly(chloro-p-xylylene) Film with Tunable Surface Wettability Prepared by Temperature and Humidity Treatment on a Polydimethylsiloxane/Silica Coating

“…Poly(chloro-p-xylylene) (PPXC) film has been extensively applied in the fields of semiconductor devices, sensors, microelectronics, material moisture protection, and so on [ 1 , 2 , 3 , 4 ]. However, it has weak hydrophobicity with a water contact angle (WCA) of only about 84° [ 5 ]. It is necessary to improve its hydrophobicity to prevent liquid water droplets from corroding or electrically shorting metallic circuits of the devices.…”