Tuning the gradient structure of highly breathable, permeable, directional water transport in bi-layered Janus fibrous membranes using electrospinning

In this paper, a novel bi-layered Janus fibrous electrospun membrane with robust moisture permeable, breathable and directional water transport properties is successfully fabricated and reported for the first time. This fibrous membrane consists of a thin inner layer of hydrophobic thermoplastic polyurethane (TPU) and a thick outer layer of super hydrophilic polyacrylonitrile (PAN). The PAN layer is coated with dopamine (PDA) to tailor the wettability. The subsequent TPU–PAN/PDA membrane demonstrates outstanding wettability and thickness gradients, which facilitate directional water transport from the TPU to the PAN/PDA layer and improve the WVT rate to 9065 g m−2 d−1 and the air permeability to 100 mm s−1 (5.0 times higher than a commercial membrane). Furthermore, a plausible mechanism explaining the bi-layered Janus fibrous membrane performance is studied. The fibrous membrane is suggested to be a promising candidate for various applications, especially in moisture-wicking clothing.