Dynamic polymorphic active colloidal assembly and optically guided reconfigurable photonics

The macroscopic properties of a material are predominantly governed by the precise arrangement of the atoms composing its crystal lattice. Recent research shows that photons can excite vibrational modes in solids that induce dynamic transitions to new phases with exotic properties. Here, we demonstrate that colloids, as a micrometer-scale “atom” counterpart, can also be assembled with light, leading to dynamic material structure and properties. This work uses photoactive colloidal particles with long-range tunable interaction, which provides a versatile route to guide assembly on demand. To induce interaction directionality for assembly, the photonic nanojet effect on a photoactive colloidal particle is exploited to create a highly localized hydrodynamic flow resembling directional molecular binding. Adjusting the illuminating condition allows the tunable directional potential to be generated on spherical colloids, forming the polymorphic assembly to all 2D Bravais lattices on demand. Finally, we reveal that the rapid colloid phase transition, as controlled with light, can be used for reconfigurable photonic devices to control the diffraction of the near-infrared laser.