Both Fig. 3a and b show that s increases with nanoparticle
concentration. Superhydrophobicity (s of water droplets > 150◦)
is achieved at the SiO2 concentration of 0.5% w/w, according to the
results of Fig. 3a. However, s keeps increasing with nanoparticle
concentration until this becomes 1% w/w. Further increase in SiO2
concentration (>1% w/w) does not have any significant effect on
s which is (i) stable, corresponding to the plateau of the curve
in Fig. 3a and (ii) extremely large (around 161◦). The behavior of
the s curve in Fig. 3a is in agreement with previously published
studies which described the effect of nanoparticle additives on the
wettability of polymer surfaces [51–54].