Controlled Microwave-Hydrolyzed Starch as a Stabilizer for Green Formulation of Aqueous Gold Nanoparticle Ink for Flexible Printed Electronics

Gold electrodes are important in some devices and certain applications where an inert, highly conductive feature is required. An aqueous gold nanoparticle (AuNP) ink suitable for inkjet printing was synthesized and formulated using starch and microwave-assisted heating. By varying the hydrolysis conditions of starch, the size, yield, and stability of the AuNP suspension can be controlled and optimized to achieve a jettable ink. The optimized formulation has a very low starch loading of only 1.75 wt % relative to gold, forming a highly stable AuNP ink, which upon drying already forms a very conductive film and sinters at low temperature. The overall synthesis protocol thus provides a greener and cheaper alternative to other AuNP synthesis methods. The sintering behavior of the film was monitored, wherein, upon heating, starch is degraded, crystallite growth increased, and the morphology changed from individual nanoparticles to a network of fused particles. The film sheet resistance decreased concomitant with these physical changes. By heating the film to at least 200 °C, a sheet resistance of <1.0 Ω/□ is achieved. This aqueous-formulated ink, therefore, offers an alternative to the usual organic solvent ink formulations used in printed electronics. It proved printing of conductive films on various substrates for possible applications in flexible electronic devices.