Significance
Membranes with asymmetric wettability (Janus membranes) bring a new feature to the field of membrane science. Here, we developed a scalable and high-precision method for imparting asymmetric wettability to the porous substrates. The thickness and surface topography of the integrated domains are tailored based on the requirements of a specific application. The developed method is scalable and is performed in a roll-to-roll manner.