Tunable two-dimensional assembly of colloidal particles in rotating electric fields

Abstract

Tunable interparticle interactions in colloidal suspensions are of great interest because of their fundamental and practical significance. In this paper we present a new experimental setup for self-assembly of colloidal particles in two-dimensional systems, where the interactions are controlled by external rotating electric fields. The maximal magnitude of the field in a suspension is 25 V/mm, the field homogeneity is better than 1% over the horizontal distance of 250 μm, and the rotation frequency is in the range of 40 Hz to 30 kHz. Based on numerical electrostatic calculations for the developed setup with eight planar electrodes, we found optimal experimental conditions and performed demonstration experiments with a suspension of 2.12 μm silica particles in water. Thanks to its technological flexibility, the setup is well suited for particle-resolved studies of fundamental generic phenomena occurring in classical liquids and solids, and therefore it should be of interest for a broad community of soft matter, photonics, and material science.

Phase diagram of two-dimensional colloids with Yukawa repulsion and dipolar attraction

“…[1][2][3] Two-dimensional (2D) colloidal crystals self-assembled in external fields can act as seeds for 3D structures used in photonics [4][5][6][7][8] as well as for porous media and membranes used for photocatalysis, electrochemical energy storage and conversion, and chemical applications. [9][10][11][12][13] Although tunable interactions can be achieved in different ways (including optical, chemical, and flow-mediated mechanisms 2 ), the use of electric [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and magnetic 16,[30][31][32][33][34][35][36][37][38][39][40][41] fields is among the most promising due to their technological flexibility, the long-range character of the obtained interactions, and the ability to change them in situ.…”

“…From a fundamental point of view, colloidal suspensions with tunable interactions allow us to perform particle-resolved studies 1,2,[42][43][44][45] to understand basic generic mechanisms of melting and crystallization, condensation and evaporation, spinodal decomposition, slow dynamics in glasses, nucleation, and coalescence, occurring in different regimes of interactions between particles. 1,26,43,[46][47][48] Dipolar attractions induced by external rotating fields have attracted interest in the framework of particle-resolved studies of 2D systems in magnetic 32,35,48 and electric 18,25,26,49 fields. These studies used 2D colloidal suspensions of particles, which were synchronously polarized by an in-plane rotating field, yielding isotropic dipolar attractions ∝1/r 3 at large distances, whose magnitude is determined by the field magnitude and the material properties of the solvent and colloids.…”

Thermodynamics and dynamics of two-dimensional systems with dipolelike repulsive interactions

“…An external electric field polarizes the particles and ion clouds in the solvent around them, inducing a (tunable) dipole-dipole interaction between the particles. Depending on the orientation of the external electric field with respect to the plane of particle confinement, the dipolar interaction potential can be either attractive [24][25][26][27] or repulsive [28][29][30][31][32][33][34].…”

Collective modes of two-dimensional classical Coulomb fluids

“…First, 2D systems play an important practical role in a broad range of phenomena occurring at fluid and solid surfaces and various interfaces. Examples are atomic monolayers and thin films on substrates, 2D electron fluid on the surface of liquid helium, 3 metallic and magnetic layer compounds, colloidally stabilized emulsions and bubbles, 4,5 colloidal particles at flat interfaces, 6,7 complex (dusty) plasma systems in ground-based laboratory conditions. [8][9][10] Second, physics in two-dimensions (2D) can be fundamentally different from that in threedimensions (3D).…”