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

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.

Using Desmotropes, Cocrystals, and Salts to Manipulate Reactivity in Mechanochemical Organic Reactions.

Performing reactions in the solid state offers the largely unexplored possibility of influencing reactivity by manipulating the solid form of the starting reactants. In this work, we explore the use of various solid forms of barbituric acid and its effect on reaction paths and kinetics in a Knoevenagel condensation reaction with vanillin. Modifications of barbituric acid included the use of its desmotrope, a cocrystal, and a salt as the starting reactant. Comparing these reactions with the reaction starting from the commercial keto tautomer of barbituric acid, we find that the reaction kinetics could be accelerated or decelerated, together with a change in the reaction mechanism. Exploring solid forms of reactants can be used as general methodology for manipulating mechanochemical reactivity, further highlighting the benefits of conducting reactions in the solid state, because many of the modifications of solids become unavailable upon dissolution.