Figure 2 shows CA and SA of paper substrates spray-coated
with different amount of SiO2 nanoparticles. The amount of
SiO2 nanoparticle coatings was adjusted by the number of
spray-coatings. As increasing the amount of SiO2 nanoparticle
coatings, hydrophobicity of the paper became higher, and SiO2
nanoparticle-coated paper showed superhydrophobicity when
the amount of SiO2 nanoparticle coatings was higher than ca.
0.4 mgsilica/cm2
paper. However, a large amount of SiO2
nanoparticles is unfavorable for transparent coatings; therefore,
in subsequent experiments, we repeated spray-coating (20−30
times) to adjust the amount of deposited SiO2 nanoparticles to
be ca. 0.4−0.5 mgsilica/cm2
paper.