Patchy Particle Assembly with a Twist
- Colloidal particles equipped with two, three, or four negatively charged patches, which endow the particles with 2-fold, 3- fold, or tetrahedral symmetries, form 1D chains, 2D layers, and 3D packings when polarized by an AC electric field.
- Two-patch particles, with 2-fold symmetry, pack into the cmm plane group and 3D packings with I4mm space group symmetry, in contrast to uncharged spherical or ellipsoidal colloids that typically crystallize into a face-centered ABC layer packing.
- Three-patch particles with 3-fold symmetry form chains having 21 screw axis symmetry. These chains pair in a manner such that the pair has 21 screw axis symmetry, in an arrangement that aligns the patches that would favor Coulombic interactions along the chain.
- Surprisingly, some chain pairs of three-patch particles form double-helix regions (see figure) 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.