(360c) Feedback Control of Electric Field Mediated Colloidal Assembly

The ability to assemble nano- and micro- components into ordered configurations provides the basis for fabricating tunable materials to manipulate electromagnetic energy (e.g., meta-materials, photonic bad gaps) for existing (e.g., photovoltaics, reconfigurable antennae) and emerging technologies (e.g., optical computing, sub-diffraction limited imaging, invisibility cloaking).  The limiting factor in assembling microscopic components into ordered materials is the inability to actively remove defects (e.g., grain boundaries, point defects) that form during assembly.  In this talk, we report the ‘batch’ assembly of colloidal crystals by guiding the dynamic evolution of a colloidal ensemble in an interfacial quadrupole electrode device.  We demonstrate a feedback method to control electric field mediated colloidal assembly based on real-time sensing and actuation.  Sensing is achieved using particle tracking and order parameter computation to quantify the degree of order during the assembly process.  Several order parameters are investigated for quantifying condensation and crystallization including radius of gyration and a geometrical parameter for hexagonal close packing.  Frequency actuates  colloidal crystal assembly and disassembly using dipole-dipole interactions and negative and positive dielectrophoresis (i.e. dipole-field interactions). These mechanisms are used to dynamically remove defects and produce single perfect colloidal crystals.