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This study provides a complete rheological characterization of 2D nanomaterial dispersions, employed as 2D-inks precursors in printed electronics. Three different 2D nanomaterials (molybdenum disulfide (MoS2), graphene, and hexagonal boron nitride(hBN)) were dispersed in a Newtonian fluid (toluene) and a viscoelastic fluid (toluene + ethyl cellulose) with different polymer concentrations. The presence of nanoparticles does not change the shear rheology of the carrier fluid. Regarding the extensional rheology, the results showed that the pinch-off phenomenon is present in all Toluene suspensions; however, the presence of the ethyl cellulose introduces elasticity in the system, even leading to the formation of beads-on-a-string, and the relaxation times of the suspensions depends on the kind of nanoparticles present in the fluid. As controlling the droplet size when dispensing 2D-inks is of paramount importance for printed electronics, as well as for many other applications, here it is presented a correlation between the rheological properties of these 2D-inks precursors and their droplet size when generated from a capillary nozzle in dripping regime.

Dense suspensions of model hard-sphere-like colloids, with different particle sizes, are examined experimentally in the glass state, under shear and extensional rheology. Under steady shear flow we detect Discontinuous Shear Thickening (DST) above a critical shear rate. Start-up shear experiments show stress overshoots in the vicinity of the onset of DST related with a change in microscopic morphology, as the sample shows dilatancy effects. The analysis of the normal stress together with direct sample observation by high speed camera, indicates the appearance of positive N1 and dilation behavior at the shear thickening onset. Dilatancy effects are detected also under extensional flow. The latter was studied through capillary breakup and filament stretching experimental setups, where liquid-like response is seen for strain rate lower than a critical strain rate and solid like-behavior for higher strain rates. Monitoring the filament thinning processes under different conditions (volume fractions and strain rates) we have created a state diagram where all responses of a hard-sphere suspension (Newtonian, shear thinning, shear thickening, dilatant) are shown. We finally compare the shear thickening response of these hard-sphere-like suspensions and glasses in shear with that in extensional flow.

Polymer nanocomposites based on 2D materials as fillers are the target in the industrial sector, but the ability to manufacture them on a large scale is very limited, and there is a lack of tools to scale up the manufacturing process of these nanocomposites. Here, for the first time, a systematic and fundamental study showing how 2D materials are inserted into the polymeric matrix in order to obtain nanocomposites using conventional and industrially scalable polymer processing machines leading to large-scale manufacturing are described. Two new strategies were used to insert pre-exfoliated 2D material into the polymer matrix, liquid-phase feeder, and solid-solid deposition. Characterizations were beyond micro and nanoscale, allowing the evaluation of the morphology for millimeter samples size. The methodologies described here are extendable to all thermoplastic polymers and 2D materials providing nanocomposites with suitable morphology to obtain singular properties and also triggering the start of the manufacturing process on a large scale., Comment: 19 pages, 13 figures, 7 tables