Ultrafast Interfacial Engineering for Quantifiable Control of Asymmetric Configurations in Nanostructured Janus Membranes

ABSTRACT Janus membranes (JMs) promise advanced liquid separations, but fabrication speed, substrate universality, and precise configurational control remain challenging. Here, we report an ultrafast and universal interfacial engineering strategy to construct JMs with desirable micro‐nano structures. Founded on a rapidly formed tannic acid/polyethyleneimine (TA/PEI) platform, the approach utilizes highly reactive stearoyl chloride (SC) for minute‐scale hydrophobic modification. Crucially, a novel physicochemical control principle is revealed. Specifically, interfacial wettability and tension are modulated at the molecular level by phytic acid (PA). Through this modulation, the membrane's physical immersion depth is governed to provide unprecedented, quantifiable control over hydrophilic layer thickness during liquid‐liquid interface modification. This enables tailored JMs exhibiting pronounced asymmetric super‐wettability (water contact angle (WCA) difference >157°) and tunable unidirectional liquid transport. Demonstrated across diverse metallic and polymeric substrates, the resulting JMs show remarkable separation performance for challenging mixtures, alongside exceptional stability. This facile and controllable strategy overcomes previous limitations in speed, universality, and regulation of asymmetric configurations, offering a versatile platform for designing nano‐engineered functional materials for sophisticated liquid separation applications.