Antifouling and antibacterial behaviors of capsaicin-based pH responsive smart coatings in marine environments

Antifouling biocides releasing restricts the longevity of antifouling coatings. Compared with the anchoring state, the releasing behavior of agents is much faster on the voyage, while the biofouling process is tougher. In this work, a series of capsaicin-based pH-triggered polyethylene glycol/capsaicin@chitosan (PEG/CAP@CS), polyvinyl alcohol (PVA)/CAP@CS and alginate (ALG)/CAP@CS multilayer films are prepared with controlling antimicrobial properties in marine environments. There are 23.70, 23.35 and 22.06 ppb CAP releasing from (PVA/CAP@CS)(20), (PEG/CAP@CS)(20) and (ALG/CAP@CS)(20) films after immersing in pH 4 solutions for 60 days, while only 13.07, 12.95 and 11.55 ppb CAP have been found in alkaline solutions after immersing for the same time, respectively. All these three types of films exhibit extraordinary pH responsive properties. They can control the CAP release at a low level in alkaline solutions, and make the CAP release fast in acid solutions. Moreover, the antibacterial properties against P.aeruginosa are outstanding about 95.84%, 95.0% and 96.91% for (PVA/CAP@CS)(20), (PEG/CAP@CS)(20) and (ALG/CAP@CS)(20) films, respectively. The bacteriostasis of (ALG/CAP@CS)(20) film keeps 92.73% after 60 days in alkaline solution, which means it is steadily controlled in the marine environment. Although with similar antibacterial properties to those of (PEG/CAP@CS)(20) film, (PVA/CAP@CS)(20) film displays the maximum decrease with about 92% in acid solution after 60 days. The ALG/CAP@CS film with the best-controlled release performance and long-term antibacterial properties provides novel guidance for developing new antifouling coatings application in the marine environment.