The E-jet printing of organic inks on organic substrates
Polyimide (PI) and Polydimethylsiloxane (PDMS) are substrates known for the fabrication of flexible electronics due to their mechanical properties. Herein, we utilized an additive manufacturing technique called electrohydrodynamic (e-jet) printing to deposit ink on top of the substrates. The E-jet printing process is a low-cost, high-resolution micro to a nanoscale printing system that fabricates flexible substrate patterns. We presented an expansible exfoliation method to produce high-quality few-layer graphene (FLG) in the present work. Characterizations such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), and Raman were tested on the graphene samples. Experimental results showed that the graphene had a thickness of 7.6 ± 2.3 nm, suggesting the presence of single-layer to few-layers graphene sheets. Also, there were no cracks or defects spotted on the graphene nanosheets. The maximum lateral dimension of hundreds nm proved that the exfoliation of graphite to graphene was indeed successful. Then, the graphene was deposited on the substrate via the e-jet customize printer with a series of controlled parameters to ensure high resolution printed lines. The thermal annealing effect on printed lines was investigated, and we found out that the optimum temperature for our substrate is 280 °C. We managed to drive down the sheet resistance of the printed lines from 138.75 Ω/sqr to 41.75 Ω/sqr. Besides that, we also explored different substrates such as Polydimethylsiloxane (PDMS) due to its high stretchability and flexibility properties. Here, a highly stretchable graphene-PDMS was fabricated using the e-jet printing method. Experimental results showed that the substrate has demonstrated stretchability up to 30% and bending up to 27mm displacement. Also, the I-V curve illustrated a linear relationship between current and voltage, which suggested that the proposed sensor demonstrated ohmic resistor behaviors. The proposed sensor suggested that it can function normally in an environment temperature below 110 °C. Besides, we also indicated the stability of the proposed sensor under stretching and bending for 10 minutes, respectively. On the whole, the proposed sensor can be used in wearable electronic applications because of its high stretchability and flexibility.