3.2. Contact angles
Fig. 3 shows measurements of static (s) and tilt (t) contact
angles of water, oil and dodecane droplets on treated silk as a
function of the SiO2 nanoparticle concentration. Attention is first
focused on the results reported for water (Fig. 3a) and oil (Fig. 3b)
droplets, which are important for practical applications. Silk samples
treated with pure siloxane correspond to s of 147.8◦ (Fig. 3a)
and 140◦ (Fig. 3b) for droplets of water and oil, respectively. These
values are high compared to the s measured when pure siloxane
was deposited on smooth glass: s = 80◦ for water and s = 43◦
for oil droplets on treated glass. It is therefore concluded that the
intrinsic roughness of the knitted silk fibers plays a key role [55] in
enhancing both the hydrophobic and oleophobic character of the
deposited coating.