Hybrid electrospun membrane based on poly(vinylidene fluoride)/poly(acrylic acid)–poly(vinyl alcohol) hydrogel for waterproof and breathable applications

To develop waterproof breathable membranes, a Janus lyophobic/lyophilic media composed of a poly(vinylidene fluoride) electrospun membrane and a hydrogel electrospun mat was proposed. Poly(vinylidene fluoride) membranes were electrospun in different electrospinning conditions to evaluate the effect of the fiber diameter on the membrane characteristics. Afterward, a layer of hydrogel was electrospun on the poly(vinylidene fluoride) electrospun mat. The hydrogel was synthesized through the esterification reaction of poly(vinyl alcohol) and poly(acrylic acid). This hybrid membrane can transfer the body-generated moisture to the environment while it prevents the penetration of liquid water from the reverse side. The proposed hybrid membrane represented improved water vapor permeability compared with the neat poly(vinylidene fluoride) membrane (from 12.6 kg/m ² /day for the neat poly(vinylidene fluoride) up to 13.6 kg/m ² /day for the hybrid) along with good water resistance (up to 70 kPa) and good windproof property (1 ml/cm ² /s in pressure drop of 500 Pa). The results indicated that molecular diffusion is the main mechanism of moisture transfer in the poly(vinylidene fluoride) membranes with the fiber diameter ranging from 132 to 1136 nm. It has been found that the experimental effective diffusion coefficient ( D _exp ) of the neat hydrogel layer (8.7 × 10 ⁻⁶ m ² /s) is much higher than the neat poly(vinylidene fluoride) membrane (approximately 4 × 10 ⁻⁶ m ² /s), signifying that apart from molecular and Knudsen diffusions, the surface diffusion has played a major active role contributing to much higher value of water vapor permeability in case of the hydrogel layer and subsequently in hybrid layers.