Binary colloidal structures assembled through Ising interactions

Abstract

new methods for inducing microscopic particles to assemble into useful macroscopic structures could open pathways for fabricating complex materials that cannot be produced by lithographic methods. Here we demonstrate a colloidal assembly technique that uses two parameters to tune the assembly of over 20 different pre-programmed structures, including kagome, honeycomb and square lattices, as well as various chain and ring configurations. We programme the assembled structures by controlling the relative concentrations and interaction strengths between spherical magnetic and non-magnetic beads, which behave as paramagnetic or diamagnetic dipoles when immersed in a ferrofluid. A comparison of our experimental observations with potential energy calculations suggests that the lowest energy configuration within binary mixtures is determined entirely by the relative dipole strengths and their relative concentrations.

Colloidal ribbons and rings from Janus magnetic rods

“…To date, experimental studies have mainly focused on materials in which electric or magnetic dipoles exist solely due to the presence of externally applied fields [7][8][9][10] . Here, we introduce a new system composed of magnetic Janus rods that possess permanent dipoles and, referring to their association as dipolar assembly, explore their assembly into unique and interesting structures with analogies to liquid crystalline materials and organic molecules.…”

Statistical analysis of phase formation in 2D colloidal systems

“…Therefore, 50% of the beads in a chains are magnetic. A variety of twodimensional lattice structures has been reported with increasing fraction of magnetic beads as the ferrofluid susceptibility was increased [28].…”

“…4(d). From the minimization of magnetostatic energy (as in the 2D case [28]) it would be expected that for increasing FF susceptibility the peak shifts to higher fractions of magnetic beads. However, the opposite is observed and the peak shifts to lower fractions of magnetic beads.…”

“…In binary systems with magnetic and non-magnetic beads the interaction between the particles can be tuned by varying the FF concentration. Therefore, a variety of structures can be observed for different particles interactions, bead ratios and densities [28]. Statistical analysis is particularly powerful for systems with many local minima in the free energy, which can result in metastable phases or frustration hindering phase transitions.…”

Polloidal Chains from Self-Assembly of Flattened Particles

“…17 The polymerization probability p is defined as the fraction of flats in flat−sphere bonds. 17 Figure 2 shows experimental data for the number fraction of polloids (particles with a = 1.1 μm and s = 0.65a) assembled at three different salt concentrations (20,25,and 30 mM KCl). To obtain the theoretical p value for each sample, the number fraction distribution with the corresponding N values was put into the classical equations described above.…”