posted on 2019-03-28, 18:33authored byZhiwei Liao, Gaoxiang Wu, Daeyeon Lee, Shu Yang
Surfaces that have superhydrophilic
characteristics are known to
exhibit extreme oil repellency under water, which is attractive for
applications including anti-fogging, water–oil separations,
and self-cleaning. However, superhydrophilic surfaces can also be
easily fouled and lose their extreme oil repellency, which limits
their usage in practical applications. In this work, we create an
anti-oil fouling coating by spray coating poly(acrylic acid) (PAA)-grafted
SiO2 nanochains (approximately 45 nm wide and 300 nm long)
onto solid surfaces, forming a nanoporous film exhibiting superhydrophilicity
(water contact angle in air ≈ 0°) and underwater superoleophobicity
(dichloroethane contact angle ≥ 165°). The polymer-grafted
nanochain assemblies exhibit extremely low contact angle hysteresis
(<1°) and small adhesion hysteresis (−0.05 mN m–1), and thus, oil can readily roll off from the surface
when the coating is immersed in water. Compared to other superhydrophilic
surfaces, we show that both the unique structure of spray-assembled
nanochains and the hygroscopic nature of PAA are essential to enable
ultrastable anti-oil fouling. Even after the PAA-grafted nanochain
coating is purposely fouled by oil, oil can be readily and completely
expelled and lifted-off from the coating within 10 s when placed under
water. Further, we show that our coating retains underwater superoleophobicity
even after being subjected to shearing under water for more than 168
h. Our approach offers a simple yet versatile method to create an
ultrastable superhydrophilic and anti-oil fouling coating via a scalable
manufacturing method.