Facile preparation of antifouling hydrogel architectures for drag reduction and oil/sea water separation

•Structured hydrogel coated substrate is fabricated viasurface self-catalyzed polymerization.•Tailorable underwater fluid transportation drag is achieved.•The corresponding maximum of drag reduction efficiency is up to 64%.•The porous hydrogel coated substrate could generate purified sea water at a high rate of permeation flux.•Longer-time application is preserved because of robust antifouling and abrasion resistance.