Switching plastic crystals of colloidal rods with electric fields

Abstract

When a crystal melts into a liquid both long-ranged positional and orientational order are lost, and long-time translational and rotational self-diffusion appear. Sometimes, these properties do not change at once, but in stages, allowing states of matter such as liquid crystals or plastic crystals with unique combinations of properties. Plastic crystals/glasses are characterized by long-ranged positional order/frozen-in-disorder but short-ranged orientational order, which is dynamic. Here we show by quantitative three-dimensional studies that charged rod-like colloidal particles form three-dimensional plastic crystals and glasses if their repulsions extend significantly beyond their length. These plastic phases can be reversibly switched to full crystals by an electric field. These new phases provide insight into the role of rotations in phase behaviour and could be useful for photonic applications.

Confinement Induced Plastic Crystal-to-Crystal Transitions in Rodlike Particles with Long-Ranged Repulsion

“…This sequence of events implies that, as far as we can determine, a continuous transition from a plastic crystal to a crystal took place. As far as we know, such a transition in the rotational behavior has not been observed in bulk phases, except when an external electric field was used [22]. Lee et al reported a similar monolayered crystal but composed of dumbbell particles with a nearly hard potential oriented perpendicular to the wall [18].…”

“…Recent advances in quantitative threedimensional (3D) real space analysis have made it possible to measure both positions and orientations of rodlike particles with high accuracy and sufficient temporal resolution [20][21][22][23]. In a 3D bulk phase at the same packing fraction of ϕ ¼ 0.0026 the rods were found to form a body centered cubic (bcc) plastic crystal and to rotate freely in all directions [22]. Confined between two parallel plates, however, their rotational freedom in the z direction (perpendicular to the walls) was now found to be completely or partially restricted as a function of the wall separation.…”

“…Therefore, we consider a system of rod-shaped particles with long-ranged electrostatic repulsion and present the unexpected observation that confinement induces plastic crystal-to-crystal transitions in the rod orientations that are synchronized with transitions in the lattice symmetry and the number of crystalline layers. Recent advances in quantitative threedimensional (3D) real space analysis have made it possible to measure both positions and orientations of rodlike particles with high accuracy and sufficient temporal resolution [20][21][22][23]. In a 3D bulk phase at the same packing fraction of ϕ ¼ 0.0026 the rods were found to form a body centered cubic (bcc) plastic crystal and to rotate freely in all directions [22].…”

Mechanistic Insight into the Synthesis of Silica-Based “Matchstick” Colloids

“…A dispersion of silica microrods has been shown to generate unique crystal phase behaviour when exposed to external electric fields. 11 One of the advantages of silica is the ease at which chemical modification of the particle surface can be achieved due to the reactivity of the terminal Si-OH bonds. A vast range of different functionalities can be attained through post-modification including, but certainly not limited to, fluorescent moieties.…”

Shear moduli in bcc-fcc structure transition of colloidal crystals

“…Depending on the strength and range of the interaction, colloidal suspensions show a variety of different phases as fluid, solid crystals with crystal lattice structures as body-centered cubic (bcc) or face-centered cubic (fcc), and even glassy morphology. [9][10][11] Besides the common spherical particles, systems composed of particles with other geometries like rods, 12,13 ellipsoids, 14,15 or cubes 16,17 were also studied recently, and some new fascinating phase behaviors have been found.…”