Multidirectional colloidal assembly in concurrent electric and magnetic fields

Abstract

a Dipolar interactions between nano-and micron sized colloids lead to their assembly into domains with well-defined local order. The particles with a single dipole induced by an external field assemble into linear chains and clusters. However, to achieve the formation of multidirectionally organized nano-or microassemblies with tunable physical characteristics, more sophisticated interaction tools are needed.Here we demonstrate that such complex interactions can be introduced in the form of two independent, non-interacting dipoles (double-dipoles) within a microparticle. We show how this can be achieved by the simultaneous application of alternating current (AC)-electric field and uniform magnetic field to dispersions of superparamagnetic microspheres. Depending on their timing and intensity, concurrent electric and magnetic fields lead to the formation of bidirectional particle chains, colloidal networks, and discrete crystals. We investigate the mechanistic details of the assembly process, and identify and classify the non-equilibrium states formed. The morphologies of different experimental states are in excellent correlation with our theoretical predictions based on Brownian dynamics simulations combined with a structural analysis based on local energy parameters. This novel methodology of introducing and interpreting double-dipolar particle interactions may assist in the assembly of colloidal coatings, dynamically reconfigurable particle networks, and bidirectional active structures.

Nonisotropic Self‐Assembly of Nanoparticles: From Compact Packing to Functional Aggregates

“…where θ is the angle between the external field and the line joining the sphere centres [43,44]. Interestingly, a dual application of electric and magnetic fields on superparamagnetic particles allows the formation of birectional chains, colloidal networks and crystals by modulating the electric field and by keeping uniform the magnetic field [45]. On the other hand, magnetic cubic nanoparticles can form 1D, 2D, 3D structures such as chains, ribbons, and large cuboids that are self-assembled with a combinaison of dipole-dipole magnetic interaction and vdW interaction [46].…”

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.…”

Membrane penetration and trapping of an active particle

“…The solution of the system of differential equations given by Eqs. (49) can more easily be obtained using the Laplace transform technique 143 . In the following, the Laplacetransformed function pairs are distinguished only by their argument while the hat is reserved to denote the spatial Fourier transforms.…”

“…In particular, self-assembled colloidal membranes have offered a novel a) Article contributed to the Topical Issue of the Journal of Chemical Physics entitled "Chemical Physics of Active Matter" edited by Olivier Dauchot and Hartmut Löwen. b) Electronic mail: abdallah.daddi.moussa.ider@uni-duesseldorf.de c) Electronic mail: hartmut.loewen@uni-duesseldorf.de framework for studying fundamental physical problems, such as geometric frustration in artificial spin-ice systems [38][39][40] , and can conveniently be built from isolated microparticles with adjustable interactions [41][42][43][44][45][46][47][48][49] . For this purpose, various types of interparticle interactions could be exploited, among which magnetic attraction stands out.…”