Water-dispersible graphene paste for flexible conductive patterns and films

Flexible electronics has emerged as an independent field and matured over the past decades due to they can provide a lot of benefits as compared with traditional rigid printed circuit boards, such as better durability, lighter weight, higher space efficiency, and improved comfort. Graphene-based electronics provide new opportunities for flexible electronics because of their superior properties including high electrical conductivity, high mechanical flexibility, high carrier mobility, and so forth. In this work, a water-dispersible graphene paste (WGP) was used as raw materials to fabricate flexible conductive patterns and films on various substrates. The water dispersions have noteworthy advantages over those obtained in organic solvents, such as low cost, absence of solvent toxicity and capacity for green chemistry compatibility with hydrophilic substrates, also avoiding post-reduction of graphene oxide (GO) to obtain electrical conductivity. The microstructures and rheological properties of the WGP were firstly studied. Then, the WGP with a high concentration of 20 mg mL-1 was directly printed on flexible substrates such as paper and PET film by a simple and low-cost stencil printing method to obtain various printed patterns. The electrical properties and durability of the printed patterns were investigated under different deformations such as bending and folding. The printed conductive patterns show a good conductivity and which can be visually demonstrated by lighting a LED bulb with a 3 V power source. The WGP conductive line on paper exhibits excellent electrical stability (~5% of relative change of resistance) after 1500 bending cycles. Moreover, after dilution of the WGP to a low concentration of 2 mg mL-1, it can be used to fabricate a flexible conductive film on PET substrate by spray coating technology, and which shows a low sheet resistance of ~14.33 Ω sq-1 at a thickness of ~5 μm. The results reveal that the WGP possess outstanding electronic properties and have great potential for the convenient fabrication of flexible and low-cost graphene based electronics on various substrates including flexible paper and plastics, by using a simple stencil printing method or spray printing technology.