Abstract
We show that micron-scale two-dimensional (2D) honeycomb microwells can significantly improve the stability of blue phase liquid crystals (BPLCs). Polymeric microwells made by direct laser writing improve various features of the blue phase (BP) including a dramatic extension of stable temperature range and a large increase both in reflectivity and thermal stability of the reflective peak wavelength. These results are mainly attributed to the omnidirectional anchoring of the isotropically oriented BP molecules at the polymer walls of the hexagonal microwells and at the top and bottom substrates. This leads to an omnidirectional stabilization of the entire BPLC system. This study not only provides a novel insight into the mechanism for the BP formation in the 2D microwell but also points to an improved route to stabilize BP using 2D microwell arrays.
Highlights
Photonic crystals (PCs) form naturally through self-ordering of spherical particles to create the iridescent colors in gem stones such as opal,[1] whereas the dynamic light manipulation properties of PCs are clearly seen in nature, for instance, in the vivid displays of cuttlefish.[2]
The blue phase (BP) is a mesophase between isotropic and chiral nematic phase, where first the liquid crystals (LCs) molecules selfassemble into double-twisted cylinders (DTCs) with disclinations among adjacent DTCs, and second these cylinders stack into woodpile-like structures with period of the order of the visible wavelength
When the temperature is higher than 49 °C, the BP material is isotropic and only the microstructure can be seen under the POM with crossed polarizers
Summary
Photonic crystals (PCs) form naturally through self-ordering of spherical particles to create the iridescent colors in gem stones such as opal,[1] whereas the dynamic light manipulation properties of PCs are clearly seen in nature, for instance, in the vivid displays of cuttlefish.[2]. By virtue of the adjustable periodicity and the specific chirality for a BP structure, a tunable photonic band gap (PBG) for circular polarizations with handedness the same as that of the helix of the DTCs10 is formed This tunable PBG and its exceptional properties (e.g., submillisecond response time) open opportunities for the BP to have application in advanced photonic devices exploiting their 3D PC properties.[11] BP usually exists in a very narrow temperature range (a few degrees) because the formation of double-twisted helical structure is energetically unfavorable and critical.[12] To overcome this significant disadvantage, various techniques, such as polymer stabilization,[13] nanoparticle doping,[14−16] photosensitive chiral doping,[17] and molecular modification,[18] have been proposed for stabilizing the BP structure and widening its stable temperature range. Article microstructures and demonstrates a new approach of developing a stabilized BP device for use in display devices or as an optical modulator
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