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Multilayered graphene based nanofluidics
thesisposted on 2017-02-27, 03:57 authored by Cheng, Chi
Graphene is a single layer of carbon atoms. It is the ultimate surface material that can divide space by its existence down to nano- or even sub-nanometer scale. Space in between two graphene sheets placed in parallel is essentially a slit channel confined by one-atom thick walls. Accordingly, stacking multiple graphene layers can achieve maximum efficiency in engendering multiple channels in a given amount of space. The research reported therein is devoted to understanding and exploring applications of the space-dependent ion transport across an array of cascading nanoslits enclosed by fuzzily confined graphene multilayers at sub-10 nm scale. This thesis is unfolded into three parts. In the first part, methods of engineering channel confinement at sub-10 nm scale is developed. The statistical channel dimension is defined by the interlayer spacing in between solvated graphene layers. By manipulating the supramolecular interactions among solvated graphene sheets, the interlayer spacing can be continuously adjusted from 0.6 to 16 nm. Based on this method of engineering interlayer spacing, in the second part, ion permeation across graphene multilayers is investigated. The circuitous geometry of the cascading nanoslits enclosed by graphene multilayers is numerically depicted which has a large length-to-height aspect ratio over 5×104. Ion transport behavior across these nanoslits is then systematically investigated. Sub-10 nm ion transport profile is experimentally revealed for the first time, showing regions of critical length scales below 2 nm where fast ion transport behaviors occur which deviate from that in bulk. The peak of non-degenerate ion transport decays in amplitude while shifts unexpectedly to larger length scales as an increase in ionic concentration. In the third part, efforts are directed towards translating these new findings in graphene-confined nanoionic flow into graphene-based technologies that mainly includes development of new characterization means for nanoporous structures and capacitive energy storage. Taking advantage of the enabling role of graphene multilayers, which is simultaneously being a unique nanofluidic platform as well as a model porous electrode, the research initiates researching nanofluidics using methodologies established in electrosorption science. Such effort not only leads to a dynamic electrosorption approach proposed as a viable characterization means for nanoporous carbon in solution phase, but also gives a semi-numerical reasoning that demonstrates the essential role of spatially efficient ion transport in achieving high density capacitive energy storage. In sum, the PhD research establishes a new multilayered graphene based nanofluidic platform that generates much needed experiment evidence for researching anomalous ion transport at sub-10 nm length scales. The work shows the great potential of multilayered graphene-based materials for high density capacitive energy storage. Most importantly, this work identifies the core characteristics with which a materials system should be endued for future applied nanofluidics, which extends the scope of current nanofluidics and applications. The thesis is concluded with personal perspectives on future directions and opportunities particularly in disciplines such as membrane technology, chromatography separation and nanofluidic energy harvesting the graphene-based nanofluidics could pursue.