Solution-phase printing of exfoliated graphene flakes is emerging as a low-cost means to create flexible electronics for numerous applications. The electrical conductivity and electrochemical reactivity of printed graphene has been shown to improve with post-print processing methods such as thermal, photonic, and laser annealing. However, to date no reports have shown the manipulation of surface wettability via post-print processing of printed graphene. Herein, we demonstrate how the energy density of a direct-pulsed laser writing (DPLW) technique can be varied to tune the hydrophobicity and electrical conductivity of the inkjet-printed graphene (IPG). Experimental results demonstrate that the DPLW process can convert the IPG surface from one that is initially hydrophilic (contact angle ∼47.7°) and electrically resistive (sheet resistance ∼21 MΩ □ −1 ) to one that is superhydrophobic (CA ∼157.2°) and electrically conductive (sheet resistance ∼1.1 kΩ □ −1 ). Molecular dynamic (MD) simulations reveal that both the nanoscale graphene flake orientation and surface chemistry of the IPG after DPLW processing induce these changes in surface wettability. Moreover, DPLW can be performed with IPG printed on thermally and chemically sensitive substrates such as flexible paper and polymers. Hence, the developed, flexible IPG electrodes treated with DPLW could be useful for a wide range of applications such as self-cleaning, wearable, or washable electronics.
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Laser Photoreduction of Graphene Aerogel Microfibers: Dynamic Electrical and Thermal Behaviors
This work reports the dynamic behaviors of graphene aerogel (GA) microfibers during and after continuous wave (CW) laser photoreduction. The reduction results in one‐order of magnitude increase in the electrical conductivity. The experimental results reveal the exact mechanisms of photoreduction as it occurs: immediate photochemical removal of oxygen functional groups causing a sharp decrease in electrical resistance and subsequent laser heating that facilitates thermal rearrangement of GO sheets towards more graphene‐like domains. X‐ray and Raman spectroscopy analysis confirm that photoreduction removes virtually all oxygen and nitrogen containing functional groups. Interestingly, a dynamic period immediately following the end of laser exposure shows a slow, gradual increase in electrical resistance, suggesting that a proportion of the electrical conductivity enhancement from photoreduction is not permanent. A two‐part experiment monitoring the resistance changes in real‐time before and after photoreduction is conducted to investigate this critical period. The thermal diffusivity evolution of the microfiber is tracked and shows an improvement of 277 % after all photoreduction experiments. A strong linear coherency between thermal diffusivity and electrical conductivity is also uncovered. This is the first known work to explore both the dynamic electrical and thermal evolution of a GO‐based aerogel during and after photoreduction.
more » « less- NSF-PAR ID:
- 10419350
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 23
- Issue:
- 23
- ISSN:
- 1439-4235
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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