Probing nanomechanical, interfacial forces, and surface potential properties of MXene-nanocellulose composites

The nanomechanical properties, interaction force origins, and surface contact potentials of poly(ionic liquid) (PIL)-modified layered MXenes (Ti₃C₂T _x ), assembled with holocellulose nanofibers (HCNFs) via solution-phase methods, were investigated using PeakForce Quantitative Nanomechanical Mapping (PFQNM) and Kelvin Probe Force Microscopy (KPFM). PFQNM results revealed that incorporation of HCNFs enhanced the structural uniformity and elastic modulus of the composite. The presence of PIL improved the flexibility of the nanomechanical property, likely due to electrostatic dominating interacting forces in colloidal phase. Force spectroscopy using a HCNF-functionalized colloidal probe demonstrated van der Waals attraction between MXene and HCNF at tip compression, and significant energy dissipation at tip retraction, likely aided by hydration forces from hydrogen bond formation. This dissipation was attributed to deformation of chemical groups on HCNFs during compression. KPFM results showed reduced surface contact potentials in PIL-treated MXenes, indicating improved charge transport properties. This effect is attributed to PIL-induced changes in surface dipolarity through electrostatic interactions between the cationic PIL and hydroxyl groups on the MXene. A further reduction in surface potential was observed in MXene-HCNF composites, likely due to residual functional groups on the HCNFs inducing strong van der Waals attraction toward the PIL-modified MXenes, thereby further altering the surface dipolarity. Overall, this study offers new insights into how nanoscale interaction forces govern the mechanical properties and surface charge behavior of MXene-HCNF composites.