Dynamic hydrophobicity of superhydrophobic PTFE-SiO2 electrospun fibrous membranes

Abstract Hydrophobicity is critical for waterproofed and breathable fibrous membranes (WBFMs). Static hydrophobicity characterized by hydrostatic pressure required for water breakthrough and/o water contact angle (WCA) are usually used to assess the waterproofness of WBFMs. Here we show that such characterization is insufficient and inconsistent with practical applications of WBFMs because of the hydrodynamic focusing effect discovered in the previous works of this group and revealed by WBFMs. Accordingly, the dynamic rather than static wettability should be evaluated to judge whether a WBFM can be really considered as waterproofed in a particular application. Herein, we report a novel experimental strategy to evaluate the dynamic hydrophobicity of WBFMs of different thicknesses comprised of rough PTFE-SiO2 electrospun fibers. Finally, the WBFMs with robust waterproofness (penetration velocity of 3.376 m s−1) and excellent breathability [water vapor transmission rate of 11.68 kg/(m2d), where d stands for day] were successfully fabricated. Their durable hydrophobicity and self-cleaning performance were also characterized. In addition, a novel theoretical formula for the critical thickness of WBFMs accounting for the fiber micro-morphology was derived. Thus, the critical WBFM thickness is linked to the surface area of the fibers. This theoretical result holds great promise of guidance for the production of WBFMs with appropriate thickness.