(3f) Feedback Controlled Colloidal Self-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.  This work demonstrates a conceptually new approach to guide the dynamic evolution of a colloidal crystal self-assembly process by using feedback control to quantitatively and reversibly guide the dynamic evolution between disordered fluid and crystalline configurations.  Models for self-assembly are used to inform feedback control laws that close the loop between real-time sensing (via order parameters) and actuation (via tunable electrical potentials).  Feedback control tunes the ordering internal components and performs active reconfiguration in colloidal crystals of a targeted size.