Fabrication of magnetic colloidal bicones and their switchable self-assembly

The creation and fabrication of novel shapes are of paramount importance for colloids to self-assemble into desired structured materials and in order to use them as model systems for fundamental studies. Here, we demonstrate a simple yet effective method to fabricate bicone-shaped colloids by using SiO₂/PS core/shell particles through a thermal stretching route. The shape parameters are tunable. The aspect ratio is found to be predictable, and the experimental results are consistent with the model calculations. The yields are high enough to be used for self-assembly studies. As an illustration, we investigate the phase behavior of particles when interacting with depletion forces and show that the particles can form hexagonal or non-hexagonal crystal lattices in quasi-two-dimensional space. The method also allows functional nanoparticles to be integrated into the cores, resulting in responsive colloidal bicones. Moreover, the magnetically responsive self-assembly of particles is demonstrated.