(217y) “Petal Effect” Superhydrophobic Surface Based On Polybenzoxazine

"Petal
effect" superhydrophobic surface based on polybenzoxazine

Juan Liu, Zhong Xin*, Xin Lu, Changlu Zhou

State key laboratory of chemistry engineering,
School of Chemical Engineering, East China University of Science and
Technology, Shanghai, 200237, China

Roses
are not only the symbol of romantic love, but also have great contribution to
the scientific researches. Rose petals show super water repellency with a CA of
about 152.4^o; however, these droplets become pinned to the surface and
cannot roll off, even when the petal is turned upside down. This phenomenon is
the "pinned effect" or "petal effect" .¹  Such surface has the potential to
transfer a droplet from a hydrophobic to a hydrophilic one². 
And that has attracted great interest for both basic research and
practical applications in recent years³.  Jiang and co-workers⁴ noted that there are hierarchical
micropapillae and nanofolds existed on the petals' surfaces of red roses. Also,
the "petal effect " surface has been prepared by adding TiO₂,⁵ 
SiO₂,⁶ and
other nanoparticles into some low surface free energy materials.
Polybenzoxazine^{7, 8} is one
type of the low surface energy materials. In this work, SiO₂
nanoparticles were added into the polybenzoxazine by one-step thermal curing
method to fabricate the "petal effect " surface.

In
our previous study⁹, we
discovered a series of non-fluorine low surface free energy polybenzoxazine:
P-tmos, MP-tmos and PTBP-tmos. The polybenzoxazine possesses a surface free
energy (¦Ã_s=14.91mJ/m²)
that is even lower than that of pure poly(tetrafluoroethylene) (PTFE) (¦Ã_s=21mJ/m²).
Although these polybenzoxazines and fluoropolymers both possess low surface
free energies, the former is cheaper to prepare, easier to process and higher
adhesive force to the substrates. Herein, the"petal
effect" superhydrophobic surface with high water-adhesion was fabricated
through adding nano-silica particles into poly(3-(trimethoxysilyl)-n-propyl-3,4-dihydro-6-methyl-2H-1,3-benzoxazine)
(poly(MP-tmos) ) with one-step thermal curing method. The surface
properties of the polybenzoxazine films were proved through contact angle
measurement. The results show that this surface is superhydrophobic with a CA
of 161.5^o, and the droplets become pinned to the surface and cannot
roll off, even when it is turned upside down. The morphological
characterization of the samples was examined by using scanning electronic
microscope(SEM). It was clearly seen that the surface had micro- and nano-
structures.

Meanwhile,
the surface possessed good resistance to ultraviolet and excellent thermal
stability. After irradiation by 254nm UV-light for several minutes, the surface
still exhibited "petal effect". The water contact angle was almost unchanged,
and the water droplet still cannot roll off.  The thermogravimetric analysis (TGA)
results indicated that the polybenzoxazine added nano SiO₂
particles, with a high char yield of 83.10%, possessed excellent thermal
stability. On the other hand , there was a strong adhesive force adhesion
between the surface and the substrate which was proved by the cross-cut method.

Keywords:
superhydrophobic; polybenzoxazine; petal
effect

Juan Liu, E-mail: juan_liu86@163.com;
Correspondence Zhong Xin, Professor, Tel.:
+86 21 64240862; Fax: +86 21 64251772, E-mail: xzh@ecust.edu.cn

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