Electric field mediated assembly of three dimensional equilibrium colloidal crystals

We report confocal laser scanning microscopy (CLSM) measurements, Monte Carlo (MC) simulations, and an analytical model of the assembly of three dimensional (3D) equilibrium colloidal crystals within quadrupole electrodes on microscope cover slip surfaces. Micron sized fluorescent silica colloids in an index matching dimethylformamide (DMF) medium enable three dimensional CSLM imaging to measure particle coordinates. By matching density profiles from CSLM measurements and MC simulations, we obtain electrostatic, dipole–field, dipole–dipole, and gravitational potentials that accurately capture the three dimensional microstructure and morphology. We also report analytical density profiles with fluid–solid coexistence by balancing gravitational and electric field mediated compression against local osmotic pressure, which agree with CSLM and MC results. These results provide fundamental information on the assembly of three dimensional equilibrium colloidal crystals in the presence of multiple external fields and with coexisting inhomogeneous fluid and solid phases.