Highly Stable Chemically Expanded Graphite-Based Conductive Ink for Multisubstrate Printed Electronics Application

The development of a conductive ink with well-defined properties such as high conductivity, stability, flexibility, low cost, and printing adaptability with a wide range of substrates and to withstand mechanical deformation remains a challenge as it is essential for the advancement of printed and flexible electronics technology. However, traditional ink based on metal nanoparticles is high in cost with poor flexibility and gets easily oxidized. In this work, we reported a stable and conductive ink based on chemically expanded graphite (CEG). The ink was formulated using liquid-phase exfoliation with ethylene glycol as a solvent and PVP as a binder without requiring the centrifugation step. The formulated ink showed a good conductivity value of 1.05 × 10 4 S/m and maintained stable electrical performance retaining functionality after 1000 bending cycles. The ink formulation accounted for good stability in current value for a period of 180 days and under different humidity conditions. Molecular dynamics simulations were conducted accounting for models of pristine graphite and CEG ink, which showed that CEG has enhanced molecular mobility and conformational flexibility, as indicated by its larger mean-square displacement and root-mean-square deviation values. Moreover, it also exhibited a greater solvent-accessible surface area and a wider interlayer spacing, meaning that more active surfaces were exposed. The free energy surface suggested greater structural disorder, which agreed with Raman spectroscopy results with a higher I D / I G ratio. The developed ink was compatible with printing on multiple substrates and was used to fabricate an interdigitated electrode demonstrating its potential for flexible and wearable printed electronic devices.