Hydrophobic, transparent waterborne polyurethane-polydimethylsiloxane composites prepared from aqueous sol-gel process and applied in corrosion protection

An amino-polydimethylsiloxane emulsion (DN100) was synthesized by aqueous sol-gel reaction. The polyurethane with single end of triethoxysilane (PUS) was also prepared with aminopropyltriethoxysilane (APTES). The DN100 was incorporated into PUS. On the one hand, the urea linkage was formed by reaction of NH2 group of DN100 and NCO group of PUS. On the other hand, the siliceous network was established by the condensation of Si-OH group from DN100 and PUS. The siliceous network was confirmed by Si-29 NMR. The intermolecular bonding of composites included hydrogen bonding and chemical crosslink was investigated at different DN100 content. Simultaneously, AFM results showed that the surface morphology of composites was impacted markedly by intermolecular bonding. Under the low concentration of DN100 content, the biphasic surface with ovaloids formed by strong hydrogen bonding. With an increase in DN100 content, the chemical crosslink play a dominating role in intermolecular bonding. The ordered hydrogen bonding was destroyed by the increasing chemical crosslink, and the ovaloid changed into fold structure on the surface accompanied with reduction in roughness. The water contact angle showed hydrophobic surface of composites. The increase of water contact angle was related to the low surface energy and roughness. The good corrosion protection of composites was verified by the salt spray testing. And the ability of protection was affected by hydrophobic surface and crosslink density.