Janus Interface Materials: A Critical Review and Comparative Study

In recent years, Janus interface materials with wettability contrast have attracted remarkable attention because of their beneficial properties and versatile potential applications in materials science including transport, purification/separation, analytical testing, and medical applications. Regarding the wide range of highly promising possible application areas, these materials will have a major impact on the next generation of smart systems. In this Review, our aim is to highlight the current status of the research on Janus interface materials with special emphasis on wettability contrast. In the first section, a brief history of the literature on Janus-type materials and interfaces, materials possessing different chemistries or topographies on opposing sites, is introduced. In the second section, theories behind wetting, including “wettability integration”, are summarized, which can be regarded as the combination of opposing wetting properties within the same material. Afterwards, natural examples of Janus interfaces, a branch of superwettability integration, are discussed, which inspired the researchers to mimic the nature and develop artificial analogues. In the next section, the current status on artificial Janus interfaces with wettability contrast are reviewed, subcategories for which are implemented according to the (possible) application areas and also the origin of their base substrates. Then, the inorganic and organic based artificial Janus interfaces were compared in terms of advantages and disadvantages. Finally, a conclusion and outlook are given.