Electric field-directed assembly of fullerene crystal rods into hierarchical films

Self-assembly of nanomaterials with desired material properties requires assembly control from nanometer to millimeter scales. Here, hierarchical C60 and C70 films are assembled from the nanoscale to macroscale by combining co-solvent precipitation with electric-field directed assembly. Fullerene molecular crystals are grown via seeded co-solvent precipitation with mixed organic solvents and antisolvent 2-propanol. Rods of varying aspect ratios (1.7, 2 and 3.7) are prepared as a function of injection volume, fullerene type and solution concentration. Electric fields are applied to colloidal fullerene rods confined to two dimensions. The applied field induces dipolar forces, dielectrophoretic forces, and electrohydrodynamic flows. Frequency-dependent phase transitions occur at the critical Maxwell–Wagner crossover frequency, where the effective polarizability of the particles in the medium is substantially reduced, resulting in changes in structure. Partial order phases form as a function of field strength, frequency, and confinement including tetratic, smectic, centered rectangular and string fluids.