Electric-Field-Induced Reversible Phase Transitions in Two-Dimensional Colloidal Crystals.
Two-dimensional colloidal crystals confined within electric field traps on the surface of a dielectrophoretic cell undergo reversible phase transitions that depend on the strength of the applied AC electric field. At low field strengths, the particles adopt a two-dimensional hexagonal close-packed lattice with p6m plane group symmetry and the maximum achievable packing fraction of φ = 0.91. Higher electric field strengths induce dipoles in the particles that provoke a phase transition to structures that depend on the number of particles confined in the trap. Whereas traps containing N = 24 particles transform to a square-packed lattice with p4m symmetry and φ = 0.79 is observed, traps of the same size containing N = 23 particles can also pack in a lattice with p2 symmetry and φ = 0.66. Traps with N = 21, 22, and 25 particles exhibit a mixture of packing structures, revealing the influence of lateral compressive forces, in addition to induced dipole interactions, in stabilizing loosely packed arrangements. These observations permit construction of a phase diagram based on adjustable parameters of electric field strength (0-750 V/cm) and particle number (N = 21-25).
Molecular Design Institute and Department of Chemistry, New York University , New York, New York, 10003, United States.
Kelsey A
KA
Collins
Molecular Design Institute and Department of Chemistry, New York University , New York, New York, 10003, United States.
Xiao
X
Zhong
Molecular Design Institute and Department of Chemistry, New York University , New York, New York, 10003, United States.
Pengcheng
P
Song
Molecular Design Institute and Department of Chemistry, New York University , New York, New York, 10003, United States.
Neva R
NR
Little
Molecular Design Institute and Department of Chemistry, New York University , New York, New York, 10003, United States.
Michael D
MD
Ward
Department of Chemical Engineering and Materials Science, Stevens Institute of Technology , Hoboken, New Jersey 07030, United States.
Stephanie S
SS
Lee