Polymer-Stabilized Blue Phase Liquid Crystals

Polymer-Stabilized Blue Phase Liquid Crystals 

An optically isotropic liquid crystal (LC) refers to a composite material system whose refractive index is isotropic macroscopically, yet its dielectric constant remains anisotropic microscopically [1]. When such a material is subject to an external electric field, induced birefringence takes place along the electric field direction if the employed LC host has a positive dielectric anisotropy (Ae). This optically isotropic medium is different from a polar Uquid crystal in an isotropic state, such as 5CB (clearing point = 35.4°C) at 50 C. The latter is not switchable because its dielectric anisotropy and optical anisotropy (birefringence) both vanish in the isotropic phase. Blue phase, which exists between cholesteric and isotropic phases, is an example of optically isotropic media. 

Fundamentals of liquid Crystal Devices, Second Edition. Deng-Ke Yang and Shin-Tson Wu. 2015 John Wiley Sons, Ltd. PubUshed 2015 by John Wiley Sons, Ltd. 

---

Jin Yan and Shin-Tson Wu, Polymer-stabilized blue phase liquid crystals a tutorial. Opt. Materials... 

Polymer-Stabilized Blue Phase Liquid Crystals... 

To widen BP temperature range, several approaches have been proposed [15-18] Here, we focus on the blue phases induced by incorporating chiral dopants into a nematic LC host. To make a polymer-stabilized blue phase liquid crystal, a small fraction of monomers (-8%) and photoinitiator (-0.5%) is added to the blue phase system. Figure 14.4 shows some exemplary nematic LC compounds, chiral dopants, and monomers [19]. Then we control the temperature within the narrow blue phase range to conduct UV curing. After UV irradiation, monomers are polymerized to form a polymer network, which stabilizes the blue phase lattice stmctures. 

Figure 14.7 Measured wavelength dependent Kerr constant (dots) of a polymer-stabilized blue phase liquid crystal and fitting results with Equation (14.21). Reproduced with permission from the American Physical Society.

L. Rao, J. Yan, S. T. Wu, et al., A large Kerr constant polymer-stabilized blue phase liquid crystal, Appl. Phys. Lett. 98, 081109 (2011). 

J. Yan and S. T. Wu, Effect of polymer concentration and composition on polymer-stabilized blue-phase liquid crystals, J. Display Technol. 7, 490-493 (2011). 

J. Yan, H. C. Cheng, S. Gauza, et al.. Extended Kerr effect of polymer-stabilized blue-phase liquid crystals, Appl Phys. Lett. 96, 071105 (2010). 

Y. Chen, and S.T. Wu, Recent advances on polymer-stabilized blue phase liquid crystal materials and... 

F. Peng, Y. Chen, J. Yuan, et al.. Low temperature and high frequency effects of polymer-stabilized blue phase liquid crystals with a large dielectric anisotropy, J. Mater. Chem. C. 2, 3597-3601 (2014). DOI 10.1039/c4tc00115j... 

Chambers M, Finkehnann H, Remskar M, Sanchez-Ferrer A, Zalar B, umer S (2009) Liquid crystal elastomer-nanoparticle systems for actuation. J Mater Chem 19 1524—1531 Chen Y, Wu ST (2014) Recent advances on polymer-stabilized blue phase liquid crystal materials and devices. J Appl Polym Sci 40556 1-10... 

---