Electrically Driven Multiaxis Rotational Dynamics of Colloidal Platelets in Nematic Liquid Crystals

Abstract

We describe field-induced multiaxis rotations of colloids in a nematic liquid crystal. Anchoring of the nematic director to the colloidal platelet's surface and interplay of dielectric and elastic energies enable robust control over colloid orientation that cannot be achieved in isotropic liquids. Because of the anisotropy of the fluid and the platelike shape of particles, the colloids can be forced to rotate about four different rotational axes even for a fixed direction of the applied field. The time scale of these unexpected voltage-dependent dynamics varies over four orders of magnitude (10⁻²-10² s) and promises a number of novel electro-optic, photonic, and display applications.

Active Shape-Morphing Elastomeric Colloids in Short-Pitch Cholesteric Liquid Crystals

“…Within a far-field approximation, even spherical particles with strong boundary conditions induce dipolar or quadrupolar n(r)-distortions arising due to the anisotropic nature of the host medium and particle-induced satellite defects, such as point defects and disclination loops [1,2]. Although many methods for self-assembly of anisotropic particles in isotropic solvents have been introduced [4], LC hosts bring a number of unique capabilities, such as the well-defined long-range alignment of anisotropic particles with respect to n controlled by external fields [3,[5][6][7][8][9][10].…”

“…Although complex-shaped particles can be fabricated using photolithography [3,6], two-photon polymerization [10], nanocrystal growth [8], and wet chemical synthesis [7,9], these approaches provide nematic dispersions of non-responsive particles with no means for altering their shape, alignment, locomotion, and self-assembly [3,[5][6][7][8].…”

“…Along with symmetry considerations, this brings about an expansion into multipole series and electrostatic analogies between long-distance colloidal interactions and that of multipoles in electrostatics [1][2][3][4][5][6][7][8][9][10][11]36]. The ground state in a CLC is strongly twisted and a direct parallel with the homogeneous nematic ground state is impossible because homogeneity of the ground state is a prerequisite of the symmetry-based considerations [11].…”

Self-assembly of colloidal particles in deformation landscapes of electrically driven layer undulations in cholesteric liquid crystals

“…Our observation that the colloidal inclusions tend to spatially localize in the regions of an undulations lattice associated with strong layer deformations indicate that particles inserted into such electrically controlled The elasticity-mediated interactions and surface anchoring-mediated alignment of colloidal inclusions in CLCs with tunable undulations patterns can be further enriched by dielectrophoretic effects (and also electrophoretic effects when these particles are charged), as we already briefly mentioned above. Even in isotropic fluid hosts, colloidal particles with dielectric constants different from that of the surrounding medium are known to strongly interact with the gradients of electric field (e.g., when these gradients are produced by using patterned electrodes) [55][56][57]. Shape-anisotropic or composition-anisotropic particles in the isotropic fluid hosts also rotate and align with respect to the applied electric field direction in order to minimize the dielectric term of the free energy [55][56][57].…”

“…Even in isotropic fluid hosts, colloidal particles with dielectric constants different from that of the surrounding medium are known to strongly interact with the gradients of electric field (e.g., when these gradients are produced by using patterned electrodes) [55][56][57]. Shape-anisotropic or composition-anisotropic particles in the isotropic fluid hosts also rotate and align with respect to the applied electric field direction in order to minimize the dielectric term of the free energy [55][56][57]. In LC host fluids with large values of dielectric anisotropy, including CLCs, these effects are dramatically enriched by the fact that the patterns of director field are also the patterns of the effective dielectric constant variations.…”