3D Printed 2D Materials using Capillary Suspensions

Abstract

This thesis presents a novel method based on capillary suspensions, to prepare the printable inks with 2D materials of graphene (2 different types: M-grade and C-grade), boron nitride and molybdenum disulphide, which are all dispersed in a primary aqueous liquid (with < 5 wt% carboxymethylcellulose polymer dispersant), with a small amount of a secondary immiscible liquid, octanol. The preparation of capillary suspensions normally leads to a dramatic change of suspension rheological properties, such as the viscosity, yield stress, storage modulus and shear modulus. In this work, the rheological properties of the 2D material-based capillary suspensions were analysed by changing the particle volume fraction, the volume ratio between the secondary liquid and the particle and the polymer concentration in the primary liquid. All rheological properties are largely increased when particle volume fraction is increased for both GNP-based and BN-based capillary suspensions. When secondary liquid/particle volume ratio was increased, the rheological properties of both GNP-based and BN-based capillary suspensions show a similar variation trend, rising to a maximum value and decreasing. However GNP-based capillary suspensions show a plateau of constant rheological behaviour before decreasing, which is not seen with the BN-based capillary suspensions. Capillary suspensions using MoS2 particles and C-grade graphene particles were also investigated. The range of capillary suspension compositions possible with MoS2 was much smaller than found with BN or the M-grade graphene particles. However, it proved to be impossible to prepare any capillary suspensions using the C-grade graphene. This behaviour correlated with the contact angles measured on these materials. Both MoS2 and the C-grade graphene particles had a contact angle with the primary liquid > 90o, which resulted in a small or even 0o three-phase contact angle. In which case, the secondary liquid prefers to cover the particle surface rather than form bridges between particles. The suitable GNP-based and BN-based capillary suspensions were 3D printed using the direct ink writing (DIW) technique. The printed GNP and BN structures have a porosity of 81% and 65%, respectively and are both robust for handling with a compression strength of 1.3 MPa and 0.7 MPa, respectively. GNP structure shows a high electrical conductivity, especially after heat treatment at 350 oC, but the strength is reduced during the heating process. These printed BN and GNP structures were cooperatively employed for a supercapacitor manufacture. X-Ray tomography of the printed GNP and BN internal structures shows that the formation of the capillary suspension eliminates ordering of the 2D materials after extrusion and the aspect ratio (length/width) of BN particle clusters is smaller than that of GNP particle clusters for both conventional suspensions and capillary suspensions.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Derby (Supervisor) & Suelen Barg (Supervisor)