Blue-phase-polymer-templated nematic with sub-millisecond broad-temperature range electro-optic switching

Abstract

We report on fast electro-optic switching (response time 0.1 ms) of a blue-phase-polymer templated nematic with a broad-temperature range of thermodynamic stability and hysteresis-free performance. The nematic fills a polymer template that imposes a periodic structure with cubic symmetry and submicron period. In the field-free state, the nematic in polymer template is optically isotropic. An applied electric field causes non-zero optical retardance. The approach thus combines beneficial structural and optical features of the blue phase (cubic structure with submicron periodicity) and superior thermodynamic stability and electro-optic switching ability of the nematic filler.Blue phases (BPs) of liquid crystals (LCs) represent an example of a frustrated soft matter system 1,2 . They are formed by chiral molecules that tend to arrange locally into structures with two axes of twist (so-called double twist). Although locally the double-twist is preferable than the single-twist structure (typical of standard cholesteric LCs), it cannot extend itself to fill the entire volume and needs to be stabilized by a lattice of topological defects-disclinations 1,2 . At the cores of disclinations, orientational order is reduced, so that the material can be considered as partially melted. This is why the BPs are typically observed only within a close proximity (one-two degrees) of the isotropic phase. Depending on arrangements of ordered and disordered regions, one distinguishes three classes of the BPs: BPI (body-centered cubic structure), BPII (simple cubic structure) and BPIII (amorphous lattice) 1,2 . In absence of an electric field, the BPs are optically isotropic, i.e., they show no birefringence. . One might hope to formulate a suitable PSBP or BP composition by using a broad-temperature range nonchiral nematic and doping it with a chiral additive, but the latter often reduces the temperature range of the resulting mixture and makes the electrooptic performance very temperature-sensitive 13 . The status of current research makes it clear that the material properties that are beneficial for the temperature stability of BPs are not necessarily beneficial for electro-optic performance. In this work, we propose an electro-optically switchable BP-polymertemplated nematic (BPTN) in which the specially formulated BP mixture is used only to create a

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

“…The accumulation of inclusions at the cores of disclinations is a general phenomenon reported for thermotropic liquid crystals (3,4,(8)(9)(10)(11)(12)15). Inclusions replace the strongly distorted director field and thus reduce the associated elastic energy of the system (4).…”

“…When an additive is attracted to the disclination core, two possible morphologies are expected: (i) continuous thread-like assembly, or (ii) a linear array of discrete beads. The disclination-templated assemblies reported so far had a threadlike shape, as observed for polymers in the so-called blue phases (15) and for molecular amphiphiles at the cores of nematic disclinations (9,10).…”

“…Such an attraction is energetically favored, as the strongly distorted disclination core region is replaced with the additive (4). The unique templating ability of disclinations has stimulated the exploration of their applications, such as the fabrication of optical materials (11), conductive microwires (12), soft magnets (13), and electrooptical devices (5,14,15).Disclinations in nematic liquid crystals are generally onedimensional structures, as the director pattern repeats itself along the line. When an additive is attracted to the disclination core, two possible morphologies are expected: (i) continuous thread-like assembly, or (ii) a linear array of discrete beads.…”

“…Such an attraction is energetically favored, as the strongly distorted disclination core region is replaced with the additive (4). The unique templating ability of disclinations has stimulated the exploration of their applications, such as the fabrication of optical materials (11), conductive microwires (12), soft magnets (13), and electrooptical devices (5,14,15).…”

Mesoscale martensitic transformation in single crystals of topological defects

“…In both cases, the lattice parameters are on the order of a few hundred nanometers (2-4). BPs exhibit selective light reflections; they have fast electro-optical switching characteristics, with submillisecond response times, and their viscosity is relatively large (3,(5)(6)(7)(8). This combination of properties offers advantages over conventional LCs for emerging applications in the realm of electro-optical and sensing technologies (5-15).…”