Orientational Control of Colloidal 2D-Layered Transition Metal Dichalcogenide Nanodiscs via Unusual Electrokinetic Response

We report an unusual response of colloidal layered transition metal dichalcogenide (TMDC) nanodiscs to the electric field, where the orientational order is created transiently only during the time-varying period of the electric field while no orientational order is created by the DC field. This result is in stark contrast to the typical electrokinetic response of various other colloidal nanoparticles, where the permanent dipole or (and) anisotropic-induced dipole creates a sustaining orientational order under the DC field. This indicates the lack of a sizable permanent dipole or (and) anisotropic-induced dipole in colloidal TMDC nanodiscs, despite their highly anisotropic lattice structure. While the orientational order is created only transiently by the time-varying field, a near-steady-state orientational order can be obtained by using an AC electric field. We demonstrate the utility of this method for the controlled orientation of colloidal nanoparticles that cannot be controlled via the usual interaction of the electric field with the nanoparticle dipole.