Zwitterion-bearing silica sol for enhancing antifouling performance and mechanical strength of transparent PDMS coatings

The simultaneous improvement of mechanical strength and inhibition of slime attachment for polydimethylsiloxane(PDMS)-based fouling-release coatings remains as a great challenge. In this work, a zwitterionic precursor (N-methoxyacylethyl)-3-aminopropyltriethoxysilane (MAPS) was co-hydrolyzed with tetraethoxysilane (TEOS) to afford zwitterion-bearing silica sols (h-MAPS). The h-MAPS was then simply blended with hydroxyl-terminated PDMS (PDMS-OH, 3060 cSt and 20,000 cSt) to fabricate zwitterion-containing PDMS coatings. The pre-hydrolysis process, including hydrolysis time and TEOS content, is critical to the transparency of the coatings. High optical transparency in the range of 88.1–91.4 % at 550 nm could be reached using appropriate h-MAPS. Both PDMS-OH (3060 cSt)- and PDMS-OH (20,000 cSt)-based coatings presented excellent resistance to slime attachment in real marine environment at relatively high h-MAPS content. An improvement in anti-protein adsorption and anti-bacteria properties was achieved for the coatings based on PDMS-OH (3060 cSt) attributed to the presence of more zwitterions at its surface. Addition of h-MAPS could increase the elastic modulus and tensile strength of PDMS coatings, particularly with high efficiency for the later one. More importantly, although the tensile strength of zwitterion-containing PDMS coatings at high h-MAPS content could be up to 15 MPa, its pseudobarnacle removal strength was lower than 0.4 MPa even after seawater immersion, indicating it retained a good fouling-release performance. As a whole, zwitterion-bearing silica sols can not only provide a new approach for introduction of zwitterions into PDMS coatings, but also efficiently solve the multiple drawbacks of PDMS-based fouling-release coatings, simultaneously.