Various printable inks were synthesised and evaluated for their effectiveness in creating EMI shielding solutions using extrusion 3D printing techniques. A straightforward mechanical mixing technique was used to formulate the primary MXene/PEDOT:PSS inks, with their rheological properties finely adjusted through the manipulation of interfacial interactions and modifications to the ink composition.
- Ink formulation, optimisation and characterisation
Figure 1 shows the formulation, characterisation, rheology investigations carried out for the inks. We successfully obtained inks suitable for 3D printing (Figure 1a). Owing to the synergy of MXene and PEDOT:PSS, the rheology can be easily adjusted by altering the ratio of MXene//PEDOT:PSS, and an excellent printability was achieved at a low solid concentration. More specifically, after optimisation, the obtained ink exhibited appropriate viscosities, moduli and yielding stresses (398-597 Pa) (Figure 1b-e), rendering it highly compatible with extrusion 3D printing techniques. All the inks were stored in a refrigerator at 4 °C before use and have a long shelf life.
- Extrusion 3D printing and post-printing treatments
Figure 2a shows printed devices using different inks. The as-printed object can retain structural integrity without noticeable deformation after freeze-drying but can be further redispersed in water by vigorous vibration, indicating the weak cross-linking structure based on highly reversible physical bonds in the ink system. To ensure shape accuracy of the printed structure, the researcher proposed a ‘freeze-thawing’ post-printing protocol. The typical procedures are as follows: first, the as-printed object was frozen. This step allows the slow formation of ice in the printed object, which can induce closer packing of solid components at the boundaries of ice crystals to form a more stable skeleton structure, as confirmed by SEM image (Figure 2c). Then the frozen object was directly thawed to further facilitate the solidification and enhance the functionality (Figure 2b,c).
- Printed device performance
Having the typical ink formulation, ink printing and post-treatment protocols established, 3D-printed EMI shields were fabricated. The thickness, shapes, structures that affect the shielding performance can be easily controlled using the 3D printing technique. High electrical conductivities ranging from 600-2000 S m-1 were achieved (Figure 3a). The printed EMI shielding demonstrated excellent shielding performance at small thicknesses, achieving shielding efficiencies ranging from 51 to 76 dB (Figure 3b). This indicates that more than 99.99999% of the incident radiation can be successfully shielded. Good mechanical properties and additional features (e.g. sensing, biocompatibility, and performance reliability over wide temperatures) were also achieved by fine-tuning the compositions of the inks (Figure 3c-h).
Publications:
Adv. Funct. Mater. 2023, 33, 2214196;
Mater. Today 2023, 66, 245-272.
