As mentioned above, the results in Fig. 3a which describe the
interaction of water droplets with the substrate are in agreement
with previously published reports [8,12–16,51] and can be
explained if we consider the effect of the nanoparticles on the morphology
of the deposited coating, revealed in the SEM image of
Fig. 2. Microscale clusters are separated by large areas in Fig. 2b
and 2c corresponding to coatings prepared using low particle concentration.
The water droplet fills these large areas existing among
the clusters. In this case, clusters act as pinning sites resulting in
an increase of t. However, it is quite possible that water does not
penetrate the nanocrevices that exist on the surface of the protruding
clusters because of the Laplace pressure. At elevated particle concentrations (Fig. 2d–f) the clusters become dense forming thus
a continuous rough surface resulting in high and low s and t
for water droplets, respectively. Superhydrophobicity and water
repellency are sustained by any surface corresponding to particle
concentration >1% w/w.