The unique combination of liquid crystals (LCs) and two-dimensional (2D) materials offers a plethora of possibilities for the development of macroscopically aligned three-dimensional (3D) macrostructures. The family of 2D transition metal carbides and nitrides (MXenes) that we discovered in 2011 has now over thirty members, which exhibit outstanding properties and offer facile solution processing for conductive MXene dispersions. Herein, we report on the self-assembled LC behavior in MXene dispersions without using any additives, surfactants, or stabilizing agents for the first time. We show that the nematic LC phase is present not only in aqueous dispersions of Ti~3~C~2~T*~x~*, but also in other MXenes including Mo~2~Ti~2~C~3~T*~x~* and Ti~2~CT*~x~*, and in various organic solvents, suggesting the widespread presence of LC phase in MXene dispersions. This discovery also leads to the first demonstration of pure, free-standing and highly conductive MXene fibers *via* wet-spinning. We show that by controlling parameters such as MXene flake size, coagulation bath, and needle gauge, we achieve tunability in the fiber porosity and density. The Ti~3~C~2~T*~x~* fibers exhibit a high conductivity of \~7,750 S cm^-1^, surpassing graphene and other existing nanomaterial-based fibers. Moreover, the Ti~3~C~2~T*~x~* fibers demonstrate a high volumetric capacitance of \~1,265 F cm^-3^ at 10 mV s^-1^, which is on par with Ti~3~C~2~T*~x~* films and also rival other fiber electrodes. Self-ordering LC behavior of MXenes allows us to combine the versatile chemistry and promising electrical and electrochemical properties of MXenes with the advantages of highly ordered structures to enhance the output performance of nanomaterial-based technologies. The approach established in this study will enable the realization of a myriad of possible functionalities through enhancing the solution-based processing of MXenes.


Mxene Liquid Crystals and Fibers

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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