Electrically induced structure transition in nematic liquid crystal droplets with conical boundary conditions

Abstract

Polymer-dispersed liquid crystal composites have been a focus of study for a long time for their unique electro-optical properties and manufacturing by "bottom-up" techniques at large scales. In this paper, nematic liquid crystal oblate droplets with conical boundary conditions (CBCs) under the action of electric field were studied by computer simulations and polarized optical microscopy. Droplets with CBCs were shown to prefer an axial-bipolar structure, which combines a pair of boojums and circular disclinations on a surface. In contrast to droplets with degenerate planar boundary conditions (PBCs), hybridization of the two structure types in droplets with CBCs leads to a two-minima energy profile, resulting in an abrupt structure transition and bistable behavior of the system. The nature of the low-energy barrier in droplets with CBCs makes it highly sensitive to external stimuli, such as electric or magnetic fields, temperature, and light. In particular, the value of the electric field of the structure reorientation in droplets with CBCs was found to be a few times smaller than the one for droplets with PBCs, and the droplet state remained stable after switching off the voltage.

Modifying Nobili-Durand surface energy for conically degenerate anchorings at the interface of liquid crystal colloids

“…wheren •n e = cos(ψ − ψ e ). This form has been used to study the nematic droplets with the conical anchoring [34]. The RP surface anchoring behaves around its minimum as…”

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

“…The specific feature of the axial-bipolar configuration is a random orientation of the bipolar axis relative to the short axis of oblate droplets (the normal to the composite film plane) formed in the sample. For this reason, the various optical textures of nematic droplets with the axial-bipolar structure are observed [47,48]. The axisymmetric twisted axial-bipolar configuration is formed in the cholesteric droplets at N 0 ≤ 2.9 under conical surface anchoring (Figures 2 and 3).…”

Nematic and Cholesteric Liquid Crystal Structures in Cells with Tangential-Conical Boundary Conditions

“…The nematic mixture LN-396 (Belarusian State Technological University, Minsk, Belarus) and LN-396 doped with the left-handed chiral additive cholesterylacetate (Sigma Aldrich, St. Louis, MO, USA) were used as a nematic and cholesteric, respectively. For the nematic mixture LN-396 the PiBMA film specifies the conical boundary conditions with the tilt angle 50 • [33][34][35] and azimuthal degeneration. The polar anchoring strength of LN-396 on the PiBMA film is W 0 ∼ 10 −6 J/m 2 [33].…”

“…PVA film orients the nematic LN-396 tangentially while PiBMA film specifies the conical boundary conditions with the tilt angle of director θ d = 50 • [33][34][35] and azimuthal degeneration. The azimuthal degeneration is eliminated by presence of rubbed PVA film on the bottom substrate specifying the director orientation with azimuthal angle ϕ 0 = 0 • .…”