Water wettability of floating graphene: Mechanism and Application

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The water wettability of a solid surface is usually changed either by using a different material for the solid surface or by coating the surface. However, research over the past eight years has shown that water can (at least partially) “see through” an atomic-thick layer of a material such as graphene, giving rise to so-called “wetting transparency” effect. This finding provides a unique opportunity for designing multi-functional devices since it means that the wettability of an atomic-thick film can be tuned by selecting an appropriate supporting substrate. The picture becomes even more appealing if the substrate is a liquid, since one can readily change the liquid underneath the graphene, thereby providing real-time control of the wettability, a capability that would be very useful for water harvesting of moisture from the air and in droplet microfluidics devices. The research objectives of this project are to use experiments and computational simulations to understand the mechanisms of wetting transparency of graphene on liquid substrates and to demonstrate the real-time control of surface wettability. This project will promote the interest and participation in research from K-12 to graduate students in many ways, e.g., by providing research training to graduate and undergraduate students, developing new courses, and conducting outreach activities. The PIs will integrate experimental and computational efforts to pursue two specific aims. First, how liquid substrates affect the wettability of graphene will be uncovered by investigating how molecular mobility, charge doping, polarization, and dispersion interactions impact the wetting transparency. Second, the range of wettability modulation as well as the mechanical robustness of floating graphene will be enhanced, and the real-time manipulation of the wettability will be demonstrated. The nature of wetting transparency of graphene on liquid substrates will be elucidated, and a state-of-the-art force field, including charge-flow polarization and many-body dispersion, will be constructed and utilized to compute the wettability of floating graphene and to establish the relative importance of various types of interactions for the wetting transparency. Using liquid as the supporting substrate opens a new dimension for designing devices with real-time wettability control, which is highly desirable in water harvesting, biomedical devices, heat exchange, micro reactors and chemical separation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.