Electrophoretic assembly and topological weaving of crumpled two-dimensional sheets with entangled defect loops

Transport, relocation, and self-assembly of nano and microparticles in colloidal systems are highly demanded in nanotechnology, photonics, microfluidics, and biotechnology; topological charges can provide an effective means for these purposes. We report that crumpled two-dimensional (2D) graphene oxide (GO) particle sheets in nematic fields can serve as a nest for complicated topological defect loops, which, in turn, provide mobility and inter-adhesiveness to the GO particles. The application of electric fields actuated the GO particles orthogonally, inducing their coalescence into large radial clusters upon absorption of other GO particles. In contrast, in the isotropic phase, where no topological defects existed, the GO particles electrostatically repelled each other owing to the presence of surface charges with equal sign. We also demonstrate that predesigned shallow surface trenches on a substrate can anchor seed GO particles, which attract other GO particles to create a macroscopic structure along the trench.

Defect loops assisted coalescence of graphene-oxide (GO) particles in nematic. Two dimensional GO sheets are easily crumpled and accommodate complicated topological defects within nematic fields. The defect loops cause GO particles to actuate and coalesce into snowflake-like clusters, under the application of electric fields. The phenomenon does not occur in isotropic medium.186