Figure 47.

(a) The treated PET surfaces shown in Figure 46 illustrating the hydrophilicity effects on a virtual water droplet positioned on top of the material for different treatment times T [min]. The original surface is at $T=0$, and the vertical scales are: (200, 200, 350, 500) nm. (b) The variation of the contact angle with treatment time expected theoretically (lines) and compared with experimental results (symbols). The images correspond to films of size 10$\mathsf{\mu }$m × 10$\mathsf{\mu }$m. In the case of the PET film, the fractal parameters are $H=0.82\pm 0.02$ and $d_{\mathrm{S}}=2.18\pm 0.02$, while for the PET tissue, they become $H=0.46\pm 0.02$ and $d_{\mathrm{S}}=2.54\pm 0.02$ (see Equation (31)) (adapted from [439]).