Segmentation-Dependent Dielectrophoretic Assembly of Multisegment Metal/Dielectric Particles

Experimental results and models for dielectrophoretic assembly of segmented metal-dielectric particles are reported. Multicomponent particles were fabricated by templated electrodeposition, silica coating, and selective etching to yield Au and solvent-filled segments in desired patterns. Both single-component particles and segmented particles that contained alternating Au and etched regions in five different patterns were produced. Frequency-dependent dielectrophoretic assembly of each particle type was observed using optical microscopy. At each frequency, a given particle type exhibited either positive or negative dielectrophoresis, accumulating at regions of highest or lowest field gradient, respectively. Crossover frequencies between positive and negative dielectrophoresis differed with segmentation pattern. Near the crossover frequency, two of the five segmented particle types exhibited a 90° rotation, reorienting such that their long axes were perpendicular to the direction of the applied field. A model treating the net particle-field interaction as a superposition of their metal and dielectric components was developed to describe the assembly behavior and was able to capture both the frequency-dependent position and orientation behaviors of the segmented particles. This superposition model was the simplest method that captured all experimental observations for realistic conductance values, outperforming models based on mixing rules for composite particles. Finally, we took advantage of our understanding of segmentation-dependent differences in dielectrophoretic response to separately control particle subpopulations in binary mixtures of multicomponent particles having different segmentation patterns. Understanding how the organization of distinct materials within multicomponent particles impacts their assembly behavior in an applied field is an important step towards particle-based reconfigurable optical devices such as responsive metamaterials.