Directed Orientation of Asymmetric Composite Dumbbells by Electric Field Induced Assembly

Abstract

Assembly and directed orientation of anisotropic particles with an external ac electric field in a range from 1 kHz to 2 MHz were studied for asymmetric composite dumbbells incorporating a silica, titania, or titania/silica (titania:silica = 75:25 vol %) sphere. The asymmetric composite dumbbells, which were composed of a polymethylmethacrylate (PMMA)-coated sphere (core-shell part) and a polystyrene (PSt) lobe, were synthesized with a soap-free emulsion polymerization to prepare PMMA-coated inorganic spheres and another soap-free emulsion polymerization to form a polystyrene (PSt) lobe from the PMMA-coated inorganic spheres. The composite dumbbells dispersed in water were directly observed with optical microscopy. The dumbbells incorporating a silica sphere oriented parallel to an electric field in the whole frequency range and they formed a pearl chain structure at a high frequency of 2 MHz. The titania-incorporated dumbbells formed chain structures, in which they contacted their core-shell parts and oriented perpendicularly to a low-frequency (kHz) field, whereas they oriented parallel to a high-frequency (MHz) field. Since the alignment of dumbbells in the chains depends not only on the interparticle forces but also on the torque that the induced dipoles in the dumbbells experience in the electric field, the orientation of dumbbells perpendicular to the electric field was the case dominated by the interparticle force, whereas the other orientation was the case dominated by the torque. The present experiments show that the incorporation of inorganic dumbbells is an effective way to control the assembled structure and orientation with an electric field.

Electrorheological fluids: smart soft matter and characteristics

“…16 shows the evolution of the concentration fluctuations. As observed by confocal microscopy, the application of an electric field was also found to be vital for controlling the selfassembly of colloidal particles and creating newly structured crystalline lattices, 185,186 in addition to the similar effect induced by oscillation shear flow. 187 In a colloidal suspension of either hard or soft silica dumbbells, the random plastic solids were transformed to fully ordered crystals by the application of an electric field due to dielectric mismatch between the particles and medium.…”

Phase behaviour of polarizable colloidal hard rods in an external electric field: A simulation study

“…Furthermore, it is well known that electric fields can be used to control not only the relative position, 1, 2 but also the orientation of such anisotropic particles. 7,8,[15][16][17][18] In the present paper, we focus on the phase behaviour of rod-like colloidal particles in the presence of an external electric field. The aim of this paper is the construction of a phase diagram corresponding to experiments recently carried out on systems of micron-sized silica rods.…”

Predicting the disorder–order transition of dielectrophoretic colloidal assembly with dielectric spectroscopy

“…For example, applying AC fields across parallel electrodes assembles monodisperse or bidisperse spherical particles by combining electrokinetic and electrohydrodynamic flows. Additionally, symmetric and hetero‐dumbbells form crystal structures and chains that can be modulated depending on the electric field frequency and particle aspect ratio in similar geometries . Although electrohydrodynamic flows play a significant role in these self‐assembly processes, the underlying particle polarization remains an important driving force and its understanding is still paramount for knowledge of the assembly parameter space.…”