Understanding nanomaterial rheology and phase behavior is of practical relevance for fluid phase manufacturing processes such as direct ink writing (DIW). This work examined the effects of sheet size and concentration on the properties of aqueous MXene dispersions. MXenes are a relatively new family of two-dimensional (2D) nanomaterials. Their exceptional electrical, electrochemical, and thermal properties are desirable for a range of practical applications. Dispersions containing small (~0.3 μm), large (~3 μm), and a bimodal mixture of sizes were investigated over a range of concentrations using cross-polarized optical microscopy (POM). Steady shear and small amplitude oscillatory (SAOS) rheology were used to further understand MXene phase behavior as a function of sheet size. The large sheets readily formed into aligned structures, though the small sheets were not observed to arrange into extended alignment. Excluded volume effects enabled the bimodal dispersions to form aligned phases at lower concentrations than the other dispersions. DIW of select dispersions confirmed the important role of dispersion microstructure and rheological properties to the microstructure of printed devices. The insights achieved from this work provide a foundation for further optimization of printed MXene devices including supercapacitors and batteries.

Aqueous MXene dispersion rheology & phase behavior: Effects of sheet size

ACS Spring 2022

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