Synthesis of MXene-epoxy nanocomposites

Abstract

This thesis explores the synthesis of MXene-epoxy nanocomposites. MXenes are a family of two-dimensional materials which display versatile chemistries that allow the material to be tuned for applications that include electrochemical storage devices, electromagnetic interference shielding devices, and catalysts, to name a few. Composites of MXenes with a variety of polymers have been produced, and they show enhanced mechanical and electrical properties. In this work, epoxy composites with MXenes are synthesized, because the use of a platelet-like filler allows property enhancements such as 2D stress transfer, and the formation of diffusion barriers and percolating thresholds. Complete exfoliation of the multilayered MXenes into their 2D sheets is desired in order to realize these property improvements. Two different techniques of producing MXene-epoxy composites are evaluated. The first is a tradition in situ polymerization technique, which involves the dispersion of the filler in a volatile solvent. Acetone was used to disperse Ti3CNTx into single layers, before the dispersion was mixed with epoxy. The other technique involves the application of laminar shear stress on multilayered Ti₃C₂T_x particles, in order to exfoliate them into single layers dispersed in the epoxy matrix. In this system, a room temperature ionic liquid (RTIL) is used as the dispersant for the filler and the initiator for epoxy cure. The problems associated with MXene exfoliation, nanoparticle dispersion, and nanocomposite synthesis are considered while evaluating these methods of synthesizing these composites. It was found that while a few single layers of Ti3CNTx were successfully exfoliated, a majority of the particles were still multilayered. The physical performance of the composite was lackluster as a result of this poor exfoliation and dispersion. The lack of covalent bonding between Ti3CNTx and epoxy, and the lack of wettability of the filler are also areas of concern. In the Ti₃C₂T_x-epoxy-RTIL composites, the exfoliation of single layers was also not accomplished. Despite approximate shear stresses experienced by the particles being higher than the theoretically predicted interlayer coupling, stacked Ti₃C₂T_x particles were observed. Instead, the Ti₃C₂T_x particles had undergone swelling, which resulted from the intercalation of the RTIL. Upon application of sufficient shear stress, intercalation of bigger molecules was observed. Better properties were also obtained, leading us to hypothesize that epoxy intercalation has occurred. The reasons for poor exfoliation and poor dispersion are detailed, and future areas of study for better understanding of the MXene-epoxy system are proposed.