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Functional materials with under-liquid dual superlyophobicity have generated a great deal of concern from researchers due to their switchable separation ability oil-water mixtures and emulsions. Conceptually, under-liquid dual superlyophobicity is a Cassie state achievable under-liquid through the synergy of an under-liquid double lyophobic surface and the construction of a highly rough surface. However, obtaining an under-liquid dual superlyophobic surface remains difficult due to its thermodynamic contradiction and complex surface composition. Herein, we successfully prepared a functional coating by modifying the mixture of cellulose nanocrystals (CNCs) and nano-TiO 2 with perfluorooctanoic acid (PFOA) via a simple method, then obtained a polyester fiber membrane with under-liquid dual superlyophobicity by roll coating method. The surface wettability of the polyester (PET) membrane was altered, transforming it from the original under-water oleophobic/under-oil superhydrophilic state to the under-water superoleophobic/under-oil superhydrophobic state after coated. The resulting membrane was applied to separate oil and water on-demand. The coated PET membrane exhibited high separation efficiency (>99 %) and high separation flux, effectively separating immiscible oil-water systems as well as oil-in-water and water-in-oil emulsions. The coated PET membrane also demonstrated the ability to perform alternate separation of oil-water mixtures through wetting, washing, and rewetting cycles, with repeated processes up to 10 times without significant reduction in separation efficiency. Furthermore, compared with the previous works, our approach offers a simpler and more convenient method for constructing under-liquid dual superlyophobic surface, making it more suitable for continuous corporate production. This study may provide inspiration for the production and application in large-scale of under-liquid dual superlyophobic membranes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)