Tunable Surface Structure Of Hydrophobic Coatings Based On Grafting Polylactic Acid Copolymers And Nano-hybrids With Silica

Grafted copolymers of 1H,1H,2H,2H-perfluorooctyl methacrylate (PFOMA) onto poly(lactic acid) (PLA) chains have been synthetized by free radical mechanism for the first time. Fourier transform infrared spectrum (FT-IR) and 1H nuclear magnetic resonance (1H NMR) analyses confirmed that PFOMA grafted onto the PLA backbone successfully, and the grafting ratio for the grafted copolymers was lower than 0.25%. Rough hydrophobic grafted copolymer coatings were fabricated by dip coating, the effect of concentration, monomer content and film-forming conditions on the hydrophobility for coating was investigated. The superhydrophobic grafted copolymer hybrid coatings with hydrophobic nano-silica particles were fabricated onto the glass plates by bionic self-assembly method. The thermal properties, hydrophobicity and apparent morphologies for both series of coatings were investigated via thermogravimetric analysis (TGA), contact angle (CA) and field emission scanning electron microscope (FE-SEM), and mechanical properties were also measured. The incorporation of the hydrophobic nano-silica increased the contact angle values from 131.2° for the copolymer to 152.0°, accompanying with the contact angle hysteresis value lower than 7°.The rough structure on coating surfaces was composed of many micron grade holes and nano-scale particles. The contact area fraction of the coating staying in the air was about 87.70% via Cassie-Baxter equation. Hydrophobic hybrid coatings mentioned above exhibited good degradability in the phosphate buffer solution, which the degradation rate was 14.2wt% during the six days.Grafted poly(lactic acid) (PLA) copolymers with methacryloxy propyl trimethoxy silane (y-MPS) were synthetized by solution copolymerization regarding BPO as the initiator, and FT-IR and 1H NMR measurements demonstrated that the existence of y-MPS grafting chains onto the poly(lactic acid) backbone. The grafting ratio for the grafted copolymers was determinated to be not more than 0.11%. Grafted copolymer coatings with and without silica sol-gel were obtained through tuning rough surface morphology. Hydrophobicity, transparency, thermal property and apparent morphology for coatings were characterized by means of contact angle (CA), ultraviolet-visible (UV-Vis) spectrum, thermogravimetry (TG) and field emission scanning electron microscope (FE-SEM), and the mechanical properties were illustrated too. The static contact angle of hybrid coatings for water reached as high as 145.0°, together with the contact angle hysteresis being lower than 10°.In terms of the coarse coating surface, the multilayer, porous and mastoid morphologies were observed simultaneously. According to Cassie-Baxter equation, the contact area fraction of the coating retained in the air was of 83.55%. Hydrophobic sol-gel coatings manifested good degradability in the phosphate buffer solution, and the experimental results showed that the degradation rate was 28.0wt%.