(680g) Enhanced Wetting Stability of Initiated Chemical Vapor Deposited (iCVD) Polydivinylbenzene Thin Films By Thermal Annealing

Authors: 
Zhao, J., North Carolina State University
Wang, M., Massachusetts Institute of Technology
Gleason, K. K., Massachusetts Institute of Technology
Modification methods for turning surface energy and wetting behavior have enabled many applications, including fouling-resistant materials, anti-icing coatings, wettability-based liquid separations, friction reduction, condensation control, etc. However, the durability of wettability is still a challenge for functional coatings. Here, we report a study on the wetting stability of polydivinylbenzene (PDVB) thin films deposited via initiated chemical vapor deposition (iCVD). We found that surface oxidation during air exposure leads to a decrease of receding water contact angles and an increase of contact angle hysteresis of iCVD PDVB over time. FTIR and XPS results indicate the formation of carbonyl and epoxy groups and the reduction of pendant vinyl groups during the oxidation process. We analyzed the oxidation process with a modified first-order kinetic model, and obtained the apparent rate constant kapp = 0.0238 ~ 0.0294 h-1. In order to inhibit the oxidation in ambient air and stabilize the wettability of iCVD PDVB, we developed an in situ thermal annealing process to further crosslink PDVB thin films in the vacuum reactor after deposition. Our thermal annealing method effectively improves the crosslinking degree of iCVD PDVB, reduces the rate of oxidation in air, and consequently enhances the long-term wettability. The advancing and receding water contact angles of annealed iCVD PDVB remain above 100∘ and 70∘, respectively, even after air exposure for 2 months. With increased degree of crosslinking, the elastic modulus of iCVD PDVB films is also improved from 4.5±0.3 GPa to 6.4±0.4 GPa after thermal annealing.
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