Tuning the microstructure and rheological properties of MXene-polymer composite ink by interaction control

Since the discovery of MXene, which has been attracting attention as an alluring two-dimensional material with a distinct structure and mechanical and electrical capabilities, numerous attempts have been made to combine MXene with polymer additives to enhance and compensate for MXene’s inherent weakness. In this work, the rheological properties of MXene (Ti₃C₂T_x)-polymer composite inks of three different polymers with various interaction with MXene particles are examined. Polyethylene glycol (PEG), which is known to physically adsorb on the surface of MXene, improved MXene dispersion while enhancing the viscoelastic property of ink. MXene ink containing polyethylenimine (PEI) was destabilized forming a viscoelastic network structure as PEI of strong positive charge adsorbed on the MXene surface to neutralize negative charge and diminish electrostatic repulsion. In the case of MXene-polyacrylic acid (PAA) composite ink, the formation of hydrogen bonds between MXene and PAA resulted in a dense network structure with high viscoelasticity. In terms of rheological property sensitivity to concentration, MXene ink without polymer additives exhibited power-law behavior with the largest exponent, whereas MXene-polymer composite inks indicated moderate sensitivity. Our findings will aid in the design of MXene-based composites with optimum rheological properties for specific processes such as 3D printing and coating.