Surface Functionalization of Ti₃C₂T_<i>x</i> MXenes in Epoxy Nanocomposites: Enhancing Conductivity, EMI Shielding, Thermal Conductivity, and Mechanical Strength

MXenes have gained significant attention as multifunctional fillers in MXene-polymer nanocomposites. However, their inherently hydrophilic surfaces pose challenges in compatibility with hydrophobic polymers such as epoxy, potentially limiting composite performance. In this study, high-crystalline Ti₃C₂T_<i>x</i> MXenes were functionalized with alkylated 3,4-dihydroxy-l-phenylalanine ligands, transforming the hydrophilic MXene flakes into a more hydrophobic form, thus significantly enhancing compatibility with the epoxy matrix. This surface functionalization enabled uniform dispersion and supported the formation of a percolation network within the epoxy matrix at a low filler loading of just 0.12 vol %. Consequently, the functionalized MXene-epoxy nanocomposites exhibited remarkable performance, including an electrical conductivity of 8200 S m^-1, outstanding electromagnetic interference (EMI) shielding effectiveness (SE) of 100 dB at 110 GHz (61 dB at 8.2 GHz), improved thermal conductivity of 1.37 W m^-1 K^-1, and a 300% increase in tensile toughness (271 KJ m^-3). These properties substantially outperformed those of their nonfunctionalized counterparts and surpassed previously reported MXene-polymer nanocomposites. This study underscores the critical role of surface functionalization in unlocking the full potential of two-dimensional (2D) MXenes in polymer composites, providing a pathway to advanced multifunctional nanocomposite materials.