Thermodynamically‐driven exfoliation and self‐assembly of pristine graphene sheets is shown to provide thermally and electrically functional polymer composites. The spreading of graphene sheets at a high energy liquid/liquid interface is driven by lowering the overall energy of the system, and provides for the formation of water‐in‐oil emulsions stabilized by overlapping graphene sheets. Polymerization of the oil phase, followed by removal of the dispersed water phase, produces inexpensive and porous composite foams. Contact between the graphene‐stabilized water droplets provides a pathway for electrical and thermal transport through the composite. Unlike other graphene foams, the graphite used to synthesize these composites is natural flake material, with no oxidation, reduction, sonication, high temperature thermal treatment, addition of surfactants, or high shear mixing required. The result is an inexpensive, low‐density material that exhibits Joule heating and displays increasing electrical conductivity with decreasing thermal conductivity.
Paper diagnostics are of growing interest due to their low cost and easy accessibility. Conductive inks, necessary for manufacturing the next generation diagnostic devices, currently face challenges such as high cost, high sintering temperatures, or harsh conditions required to remove stabilizers. Here we report an effective, inexpensive, and environmentally friendly approach to graphene ink that is suitable for screen printing onto paper substrates. The ink formulation contains only pristine graphite, water, and non-toxic alkanes formed by an interfacial trapping method in which graphite spontaneously exfoliates to graphene. The result is a viscous graphene stabilized water-in-oil emulsion-based ink. This ink does not require sintering, but drying at 90 °C or brief microwaving can improve the conductivity. The production requires only 40 s of shaking to form the emulsion. The sheet resistance of the ink is approximately 600 Ω/sq at a thickness of less than 6 µm, and the ink can be stabilized by as little as 1 wt% graphite.
more » « less- PAR ID:
- 10198789
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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