Percolative dielectric behavior of titanium carbide MXene/cellulose nanofibrils composite films

Cellulose-based nanomaterials are fascinating renewable biosystems, yet low thermal conductivity and dielectric permittivity often limit their potential applications in flexible electronics. We report dielectric properties of composite films prepared by vacuum filtration or solvent casting method from the native (CNF) or carboxylated (TCNF) cellulose nanofibrils and high electrically and thermally conductive 2D titanium carbide (Ti3C2Tx) MXenes. Measurements over broad frequency and temperature ranges revealed the influence of preparation method and type of nanofibrils matrix on the overall dielectric response, as well as a notable impact of absorbed water, particularly on the cellulose’s secondary β and γ relaxations. A detailed investigation of material with the lowest amount of impurities, vacuum-filtered MXene/CNF composites, confirmed that the dielectric response follows the predictions of the percolation theory. The resulting strong enhancement of the dielectric permittivity on increasing MXene content demonstrates the potential of developed composites for applications in eco-friendly dielectric and piezoelectric devices.