Various life forms in nature display a high level of adaptability to their environments through the use of sophisticated material interfaces. This is exemplified by numerous biological systems, such as the self-cleaning of lotus leaves, the water-walking abilities of water striders and spiders, the ultra-slipperiness of pitcher plants, the directional liquid adhesion of butterfly wings, and the water collection capabilities of beetles, spider webs, and cacti. The versatile interactions of these natural surfaces with fluids, or special wettability, are enabled by their unique micro/nanoscale surface structures and intrinsic material properties. Many of these biological designs and principles have inspired new classes of functional interfacial materials, which have remarkable potential to solve some of the engineering challenges for industrial and biomedical applications. In this article, we provide a snapshot of the state of the art of biologically inspired materials with special wettability, and discuss some promising future directions for the field.

Bioinspired surfaces with special wettability have rapidly emerged at the forefront of materials research. What is behind biological surfaces with special wettability, and how can we realize special wettability properties for artificial materials? This article describes how the interplay between unique multiscale (micro- and nanoscale) structures of biological surfaces and intrinsic material properties plays a crucial role in achieving the desired wettability and functionalities. Taking inspiration from natural surfaces, researchers have designed and created novel interfacial materials with versatile special wettability, such as superantiwetting surfaces (superhydrophobic and superoleophobic), smart switchable surfaces, and water collecting surfaces.

Surfaces that display liquid contact angles greater than 150° along with low contact angle hysteresis for liquids with both high and low surface tension values are known as superomniphobic surfaces. Such surfaces are of interest for a diverse array of applications, including self-cleaning surfaces, nonfouling surfaces, stain-free clothing, spill-resistant protective wear, drag reduction, and fingerprint-resistant surfaces. Recently, significant advances have been made in understanding the criteria required to design superomniphobic surfaces. In this article, we discuss the roles of surface energy, roughness, re-entrant texture, and hierarchical structure in fabricating superomniphobic surfaces. We also provide a review of different superomniphobic surfaces reported recently in the literature and emphasize the need for mechanical, chemical, and radiation durability of superomniphobic surfaces for practical applications. Finally, we conclude with a discussion of the unresolved challenges in developing durable superomniphobic surfaces that define the scope for further improvements in the field.

Directional textured surfaces help butterflies to shed water from their wings, pitcher plants to capture prey, and water striders and certain beetles and spiders to walk on water. Inspired by natural directional surfaces, researchers have developed a myriad of synthetic surfaces with precisely tuned physicochemical properties to regulate wettable adhesion. Anisotropic surfaces are of great value to the energy and biomedical fields for applications such as directional syringes, microprocessor cooling, high-efficiency hydropower turbines, and nanoscale digital fluidics. We summarize experimental and theoretical approaches to the design, synthesis, and characterization of engineered surfaces demonstrating anisotropic wetting properties.

Condensation is a phase change phenomenon often encountered in nature, as well as used in industry for applications including power generation, thermal management, desalination, and environmental control. For the past eight decades, researchers have focused on creating surfaces allowing condensed droplets to be easily removed by gravity for enhanced heat transfer performance. Recent advancements in nanofabrication have enabled increased control of surface structuring for the development of superhydrophobic surfaces with even higher droplet mobility and, in some cases, coalescence-induced droplet jumping. Here, we provide a review of new insights gained to tailor superhydrophobic surfaces for enhanced condensation heat transfer considering the role of surface structure, nucleation density, droplet morphology, and droplet dynamics. Furthermore, we identify challenges and new opportunities to advance these surfaces for broad implementation in thermofluidic systems.

Surface wettability has emerged as a powerful tool to influence phase change phenomena such as ice formation and steam condensation. Ice mitigation using passive coatings offers tremendous promise; however, there remain several fundamental, durability- and manufacturing-related challenges that need to be addressed to harness the benefits of these coatings. Challenges limiting industrial utilization of such coatings can be classified into three categories: fundamental (frost buildup, non-zero ice adhesion, bulk ice nucleation, variable icing conditions), durability-related (harsh environment resistance, liquid impact resistance, erosion, fatigue), and manufacturing-related (scalability, coating economics). The role of passive surfaces in enhancing condensation heat transfer is a potential game changer in power plant efficiency enhancement; however, the benefits of such coatings will only be realized when durability and manufacturing challenges have been fully addressed.

There are numerous applications of nanoporous materials, including gas storage, separation, and purification. In recent years, the number of available nanoporous materials has increased substantially, with new material classes, such as metal-organic frameworks and microporous organic polymers, joining the traditional adsorbents, which include activated carbons, porous silicas, and zeolites. The determination of the gas adsorption properties of these materials is critical to both the development of new materials for targeted applications and the assessment of the suitability of a material for a particular technology. In this article, we provide an overview of nanoporous materials and their gas adsorption properties, existing and future applications for new materials, adsorption measurement methods, and the experimental challenges involved in the determination of gas adsorption both at elevated pressures and from multicomponent mixtures.