3.4.2. Water Contact Angle

Figure 7 shows that the water contact angles of PU were much lower than PUSX for both the nanofibers and films. This phenomenon might be caused by the high hydrophobicity of the silicone structure. It also proved the results of water retention when comparing PU and PUSX materials. The PUSX nanofibers showed higher WCA than the films, because the surface of the nonwoven nanofiber membrane was much rougher than the films. The pores of the nanofibers make the surface microstructure similar to the lotus structure of Cassie's state (Figure 7h).

It is worth mentioning that for graft-type PUSX nanofibers, the water retention appeared to be higher compared with the block-type PUSX nanofibers, but the results of the water contact angle were similar. This might be caused by the different surfaces of the block-type and graft-type nanofibers. It is supposed that the silicone groups were distributed differently on the graft-type PUSX nanofibers than on the block-type PUSX nanofibers.

**Figure 7.** Comparison of water contact angle (WCA, degrees). (**a**) Block-type PUSX nanofibers and films with various chain lengths, (**b**) Block-type PUSX nanofibers and films with various silicone concentrations (**c**). WCA images of (**d**) PU nanofibers, (**e**) PUSX Si08 nanofibers, (**f**) PU films, (**g**) PUSX Si08 films, and (**h**) the Lotus microstructure (Cassie's state).
