Bioinspired Self-cleaning Materials - Biotechnologies and Biomimetics for Civil Engineering - page 223

Fig. 9.14 Optical images of a water droplet on the surface of a film composed of ZnO hollow
microspheres with 2D nanosheet stacks (Adapted with permission from Sun et al. 2013 )
surface nanostructuring with low surface tension—conferred by coating the
modified surface with a fluorocarbon-based emulsion—allowed to reach and
exceed contact angles of 150 and low sliding angles.
CNT-modified glass surfaces were produced with 80 % transmittance in the
visible region, overcoming the issue of transparency related to the use of CNTs
coatings (Bu and Oei 2010 ; Meng and Park 2010 ).
The possibility of achieving switchable superhydrophilic/superhydrophobic
surfaces is also of great interest, in order to produce surfaces with controllable
interactions with water: this was achieved with CTNs (Men et al. 2010 ), as well as
with ZnO (Sun et al. 2013 ) (Fig. 9.14 ) and TiO 2 (Lai et al. 2012 ), which allowed to
maintain a transparency of 80 %.
SiO 2 nanoparticles were also employed by Gao et al. ( 2011 ) to produce the
opposite effect—i.e., superhydrophilic glass surfaces with contact angles varying
in the range 0 7 20 depending on the formation conditions of SiO 2 layers. SiO 2 /
TiO 2 composite films also find wide application in this field, owing to the
simultaneous obtaining of self-cleaning and antireflective conditions (Zhang et al.
2013a ).
9.4 Concluding Remarks
Nature is a constant source of inspiration for technological innovations, as
described in this review on bioinspired self-cleaning surfaces. Such materials have
already proved their valuable help in reducing surface soiling, which is of particular
interest in the built environment, where building envelope materials undergo a
constant soiling operated by atmospheric contaminants. The development of self-
cleaning materials—and of the related properties of antifogging, low adhesion,
antifouling, and possibly antireflection—contribute to the field of green technolo-
gies through a reduction in maintenance costs and energetic consumptions.
The working mechanism of the different self-cleaning technologies discussed is
summarized in Fig. 9.15 in order to provide a comparison among their potential
efficiency.