Fabrication of breathable Janus membranes with gradient unidirectional permeability by micro-imprinting

The realization of the directional water transport function of Janus membrane is based on the formation of its asymmetric structure. Nevertheless, the persistent problems of unstable directional water transport and poor adhesion between membranes limit their application. In this paper, based on electrospinning, the copper mesh with an in-situ growth conical nanoneedle structure was innovatively selected as an imprint template, and the conical structure was imprinted between the blended TPU/PAN membrane and the PAN membrane to form a three-layer laminated composite membrane. The gradient unidirectional permeability Janus membrane was developed, which not only constructed an asymmetric hierarchical structure but also realized the progressive wetting function inside. The water absorption tests showed that the water storage capacity was as high as 2047.37% of its weight. Moreover, stable gas permeability could be achieved under 20 cm water column pressure when the gas flow rate was 0.05 kg/cm3. Importantly, the membrane exhibited ultra-stable unidirectional water transport under strong mechanical stimulation and prolonged gravity, which provided possibility for preparation of Janus membranes with high durability, strong mechanical damage resistance and good air permeability.