CHAPTER 9: Magnetic Assembly and Tuning of Colloidal Responsive Photonic Nanostructures

The interest in self‐assembly of magnetically dipolar colloids has been driven both fundamentally and practically. Colloidal dipolar spheres are interesting model systems in condensed‐matter physics as they can self‐assemble into various crystals structures that allow exploration of the phase complexity in a single sample as their interparticle interactions can be conveniently tuned within an experimentally accessible timescale. On the other hand, magnetic assembly of colloidal particles provides an effect route towards the fabrication of functional materials, particularly colloidal responsive photonic nanostructures. In this chapter, we present recent efforts towards magnetic assembly of colloidal responsive photonic nanostructures. We start with the introduction of magnetic interactions experienced by magnetic dipolar particles in suspensions. By controlling the local particle concentration and the interparticle potential, magnetic fields not only induce the self‐assembly of colloidal particles into 1D, 2D and 3D structures, but also cause the phase transitions between different structures. A magnetic field has also been considered as a convenient stimulus to tune the optical properties of photonic structures by affecting the lattice constant d, the orientation θ, or the crystal structures. Thanks to the correlation between the photonic response and the interparticle distance, we also demonstrate that the use of magnetically responsive photonic assemblies for studying fundamental problems about colloidal interactions. By taking advantage of the unique features of the magnetically responsive photonic system, we also highlight several unique practical in structural colour printing, anticounterfeiting devices, humidity sensors, and rewritable paper.