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. 2022 Aug 25;12(17):2936.
doi: 10.3390/nano12172936.

Conductive Inks Based on Melamine Intercalated Graphene Nanosheets for Inkjet Printed Flexible Electronics

Magdalena Kralj  1 , Sara Krivačić  2 , Irena Ivanišević  2 , Marko Zubak  2 , Antonio Supina  3 , Marijan Marciuš  4 , Ivan Halasz  1 , Petar Kassal  2
Affiliations

Conductive Inks Based on Melamine Intercalated Graphene Nanosheets for Inkjet Printed Flexible Electronics

Magdalena Kralj et al. Nanomaterials (Basel). .

Abstract

With the growing number of flexible electronics applications, environmentally benign ways of mass-producing graphene electronics are sought. In this study, we present a scalable mechanochemical route for the exfoliation of graphite in a planetary ball mill with melamine to form melamine-intercalated graphene nanosheets (M-GNS). M-GNS morphology was evaluated, revealing small particles, down to 14 nm in diameter and 0.4 nm thick. The M-GNS were used as a functional material in the formulation of an inkjet-printable conductive ink, based on green solvents: water, ethanol, and ethylene glycol. The ink satisfied restrictions regarding stability and nanoparticle size; in addition, it was successfully inkjet printed on plastic sheets. Thermal and photonic post-print processing were evaluated as a means of reducing the electrical resistance of the printed features. Minimal sheet resistance values (5 kΩ/sq for 10 printed layers and 626 Ω/sq for 20 printed layers) were obtained on polyimide sheets, after thermal annealing for 1 h at 400 °C and a subsequent single intense pulsed light flash. Lastly, a proof-of-concept simple flexible printed circuit consisting of a battery-powered LED was realized. The demonstrated approach presents an environmentally friendly alternative to mass-producing graphene-based printed flexible electronics.

Keywords: conductive ink; graphene nanosheets; inkjet printing; mechanochemistry; printed electronics.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Fourier-transform infrared (FTIR) spectra for the raw sample of melamine-intercalated graphene nanosheets (M-GNS).
Figure 2
Figure 2
(a,b) Scanning electron microscopy (SEM) images and (c,d) energy-dispersive X-ray (EDX) spectra of the raw M-GNS.
Figure 3
Figure 3
Atomic force microscopy (AFM) images and cross-section analysis of the M-GNS dispersed in a mixture of ethanol:water:EG = 0.50:0.45:0.05. The sample was spin-coated on freshly cleaved mica substrates and was dried in a vacuum oven for 2 h at (a) 70 °C and (b,c) 130 °C.
Figure 4
Figure 4
Thermogravimetric analysis (TGA) curve showing the mass loss profile of M-GNS.
Figure 5
Figure 5
(a) The M-GNS ink after 24 h at rest after preparation; and (b) a histogram of the prepared M-GNS ink from Dynamic light scattering (DLS) measurements, recorded in an aqueous medium with a sample dilution of φ = 1:33.
Figure 6
Figure 6
(a) A comparison of UV–Vis spectra recorded immediately after ink preparation (day 0), and 1, 4, 25 and 32 days post-preparation (dilution: 100×); (b) the normalized view of the absorption at 514 nm (dilution: 100×); (b) inset sedimentation of the ink within the first six hours after ink preparation.
Figure 7
Figure 7
(a) The different number of printing passes of the conductive ink on a PET and PI substrate; (b) the sheet resistance of printed squares on PI, after thermal annealing at different temperatures. Error bars represent one standard deviation (n = 6); red diamond indicates the sheet resistance value after intense pulsed light (IPL) annealing at the energy of 700 J; examples of flexible printed electronics using 10 layers (c) and 20 layers (d) of the M-GNS ink.
Figure 8
Figure 8
SEM (under different magnification) and AFM images of the M-GNS film on a PI substrate: (a–c) before annealing; and (d–f) after annealing at 400 °C.
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