Abstract
Conventional 3D printing of graphene requires either a complex formulation of the ink with large quantities of polymers or essential post-processing steps such as freeze drying to allow printability. Here we present a graphene capillary suspension (GCS) containing 16.67 wt% graphene nanoparticles in aqueous suspension with 3.97 wt% carboxymethyl cellulose (CMC) as a stabiliser and a small quantity of the immiscible liquid octanol. This is shown to have the appropriate rheological properties for 3D printing, which is demonstrated through the fabrication of a simple lattice structure by direct writing and air drying at room temperature. The printed structure has a porosity of 81%, is robust for handling with a compression strength of 1.3 MPa and has an electrical conductivity of 250 S m-1. After heat treatment at 350 °C conductivity is 2370 S m-1 but the strength reduces to 0.4 MPa. X-Ray tomography of the internal architecture after printing shows the formation of the capillary suspension eliminates ordering of the 2D materials during extrusion through the printer nozzle. Thus capillary suspensions can be used to direct write graphene 3D structures without the necessity of complicated drying steps or burn-out of large quantities of polymer additions, facilitating shape retention and property control as compared to current 2D material ink formulations used for 3D printing.
Highlights
We propose an alternative method, using simpler graphene ink formulations based on the principles of capillary suspensions.[21]
The graphene phase is stabilised in aqueous suspension through the presence of 3.97 wt% carboxymethyl cellulose (CMC) in solution and the addition of a small quantity of the immiscible liquid octanol
The rheological behaviour of the three fluids used in the study: graphene capillary suspension (GCS) containing 16.67 wt% GNP and 2 vol% octanol, graphene suspension (GS) containing 16.67 wt% GNP but without octanol and the parent CMC solution were investigated through measurements of the dynamic modulus (Fig. 2a) and viscosity (Fig. 2b)
Summary
We propose an alternative method, using simpler graphene ink formulations based on the principles of capillary suspensions.[21]. The bridges rapidly reform through capillarity and the rigid structure re-emerges, i.e. a yield stress and shear thinning behaviour is seen.[22] Capillary suspensions have been used as inks with appropriate rheological properties for direct write 3D printing of alumina[23] and polydimethylsiloxane.[24] This study investigates whether the conditions proposed for the stability of capillary suspensions, which were tested on roughly equiaxed particle suspensions, are applicable for suspensions of 2D materials such as graphene.
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