Understanding interfacial gas retention under water: A materials approach using aligned carbon nanotube architectures

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Plants and animals have evolved over millions of years highly complex hierarchical structured surfaces as an adaptation to particular environmental conditions. Some insects, spiders and plants are even able to maintain persistent gas layers under water. These air layers and the different supporting structures serve as “living role models” for the biomimetic all carbon based material system employed in this research project. The project focusses on super hydrophobic gas retaining vertically aligned carbon nanotubes (VACNTs). The collaborative research project aims to explore the physical and chemical material fundamentals allowing gas retention under water and other solvents. CNTs and especially VACNTs have been established as valuable materials with widely tunable chemical and physical properties including their alignment and chemical surface functionalization. The amazing variability of this material which can be tailored in length, diameter, elasticity, chemical functionality, providing a variety of important properties (e.g. mechanical strength, pH and corrosion and fouling resistivity) will enable extensive studies on the basics of gas retention under water. It is unique and can serve as a model structure to gain deeper insight into the interfacial material properties like physical surface structure and chemical surface functionality which are both necessary to obtain such a behavior. What general impact might a deeper and complete understanding on materials development in the area of gas retention materials have? Understanding the fundamentals of gas and air retention in the proposed VACNT model system will lay the foundation for the future utilization of under water air retaining surfaces which have applications in various fields of engineering and science going from drag reduction or gas exchange to sensory systems. Whereas drag reduction has already been in the focus of engineers and biologists areas like pressure sensing and gas exchange are so far only sparsely studied and understood. This can be attributed to a lack of either straightforward accessible materials or elaborate techniques to obtain those or a combination of both reasons. With the usage of VACNTs as model material this could be overcome and tailoring the geometric (physical) and surface (chemical) properties with respect to the gas-water interface will enable us to unravel the factors which govern their gas retention properties. Specific tasks in this proposal which will be addressed to reach these goals are: Tuning of the physical and chemical surface properties of VACNTs by adjusting their geometrical parameters (diameter, distance, height, inclinement) and their surface chemistry (tuning hydrophobicity by surface functionalization). Determining the shape and stability of the water-gas interface with respect to size, stability towards different pressure conditions modification of the gas environment, exchange of gases and solvent environment.