Segmentation-Dependent Dielectrophoretic Assembly of Multisegment Metal/Dielectric Particles

Abstract

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.

Effect of Particle Composition on Dielectrophoretic Co-Assemblies around Topographic Features: Experiment and Theory

“…Field-reconfigurable optical materials with two or more distinct particle types having different optical responses could enable more elaborate tunable optics than are possible for single particle types, particularly if the different particle types can be independently addressed to mix/demix or assemble them to different locations or organizations. Dielectrophoresis (DEP)-directed assembly of binary particle mixtures where both particle types have the same composition but differ in size, surface groups, surface charge densities, or concentration ratios has been studied to understand how particles interact and assemble together. − DEP has also been used in conjunction with topographical features, often for bioseparations, such as the separation and isolation of cells or biomaterials depending upon their properties (i.e., live or dead). − Nonbiological particles have also been separated via DEP. − To date, there has been significantly less focus on the DEP co-assembly of binary particle mixtures of differing materials ,, and relatively little consideration for the optical implications and functionality of the generated systems. For example, Demirörs and Alison co-assembled polystyrene and silica particles of differing size in the vicinity of photoresist posts, taking advantage of field-induced dipolar interactions between the particles to produce colloidal superstructures, including Saturn ring-like and candle flame-like structures .…”

“…45−48 Nonbiological particles have also been separated via DEP. 49−51 To date, there has been significantly less focus on the DEP co-assembly of binary particle mixtures of differing materials 35,52,53 and relatively little consideration for the optical implications and functionality of the generated systems. For example, Demirors and Alison coassembled polystyrene and silica particles of differing size in the vicinity of photoresist posts, taking advantage of field-induced dipolar interactions between the particles to produce colloidal superstructures, including Saturn ring-like and candle flame-like structures.…”

Directed Concentrating of Micro-/Nanoparticles via Near-Infrared Laser Generated Plasmonic Microbubbles

“…Many techniques have been demonstrated using forces and fields of various origins. Electrokinetic mechanisms including electrophoresis, dielectrophoresis (DEP), and electroosmotic flow have been employed to separate and/or concentrate cells according to their bulk and/or surface electrical properties. − Acoustic mechanisms such as standing bulk/surface wave and traveling wave have also been implemented . When cells are tagged with magnetic materials, they become manipulatable by magnetic fields .…”