Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission

Novel hydrophobic/hydrophilic Janus fibrous membranes, the poly[4,4′-methylenebis (phenylisocyanate)-alt-1,4-butanediol/di(propylene glycol)/plycaprolactone] (PU) fibrous membrane as the hydrophobic layer and cellulose acetate (CA) fibrous membrane as the hydrophilic layer, were fabricated by the so-called “layer-by-layer” electrospinning technology. A series of the PU/CA Janus membranes with different electrospinning time of the CA layers by which the thickness of hydrophilic layer can be controlled were also prepared to uncover its influence on the directional water vapor transmission. The results showed that water vapor transmission capability from the hydrophobic side to the hydrophilic side of the PU/CA Janus fibrous membrane was enhanced rather than that from the reverse direction of the same membrane. The optimal water vapor transmission capacity existed when the electrospinning time of CA fibrous membrane reached 15 min. Such enhanced water vapor transmission originated because of the asymmetric wettability of the Janus membrane and the strong force to draw tiny water droplet from the hydrophobic side to the hydrophilic side. The novel understanding is useful for facile designing and fabrication of efficient moisture permeable fabrics and clothing.