(256s) Patchy Particle Under Electric Fields

We introduce patchy particles with well-defined geometries and investigate their packing and propulsion behavior under AC electric fields. Polymeric colloidal particles equipped with two, three, or four
 surface patches, which endow the particles with 2-fold, 3-
fold, or tetrahedral symmetries, form 1D chains, 2D layers, and 3D 
packings when polarized by the AC electric field. Two-patch particles pack into the cmm plane group and 3D packings with I4mm space
group symmetry. Three-patch particles form chains having a
 2(1) screw axis symmetry, but these chains pair in a manner such that
each individual chain has one-fold symmetry but the pair has 2(1) screw 
axis symmetry. Surprisingly, some chain
 pairs form unanticipated double-helix regions that result from mutual twisting of the chains about each other, illustrating a kind of polymorphism that may be associated with nucleation from short chain pairs. Larger 2D domains of the three-patch particles crystallize in the p6m plane group with alignment (with respect to the field) and packing densities that suggest random disorder in the domains, whereas four-patch particles form 2D domains in which close-packed rows are aligned with the field.

When a layer of gold is site-specifically plated on the patches, each of the aforementioned patchy particles is capable of “swimming” or propelling under electric fields driven by induced-charge electroosmosis. The propulsion behavior, for example the speed of movement and the ability to steer can be regulated by tuning the particles’ patch configurations. As a proof of concept, two-patch particles are primarily demonstrated. For particles with bent patches of the same size, the speed of swimming is related to the patch angle and the size of the particle body; for particle with a small and a big patch, the speed of swimming is mainly determined by the big patch, while the steering and curvature is dominated by the size and position of the small patch.