Electric-Field-Induced Lock-and-Key Interactions between Colloidal Spheres and Bowls

To
realize new and directed self-assembly (SA) pathways, the focus
in colloid science and nanoscience has shifted from spherical particles
and interactions to increasingly more complex shapes and interparticle
potentials. This field is fueled by recent breakthroughs in particle
synthesis, such as particles with complementary shapes that allow
for specific lock-and-key interactions induced by depletants. Here,
we show that electric fields form an alternative route for directing
the SA of convex and concave colloids, with the additional advantage
that the system now becomes switchable by external conditions. Both
experimental and theoretical results are presented that validate the
electric-field-induced assembly mechanism and show that even irreversibly
bound composites can be generated by tuning the force balance. The
successful isolation of the irreversible composite particles, in combination
with generalization to different materials, shows that the current
mechanism provides a versatile new path not only toward complex-particle
synthesis but also toward directed self-assembly.