Session Index

In recently discovered Twist-Bend Nematic (NTB) phase based on bent-core or bimesogen liquid crystals, the nematic director is spontaneously distorted and twisted along a conical helix with an extremely short pitch, ~10 nm [1-5]. Due to the periodic NTB structure, many investigations have shown the electro-optic effects are not nematic-like but are close analogs to those in the chiral smectic A and cholesteric phases. In particular, these studies have shown fast (sub-microsecond) flexoelectrically-induced rotation of the optic axis, which is similar to the electroclinic effect in the SmA* phase and the flexoelectric response of short-pitch cholesterics [6-10]. A linear electro-optic effect in a cholesteric liquid crystal is described and attributed to the flexoelectric effect. An electric field applied perpendicular to the helix axis rotates the director about an axis parallel to the field. This produces a periodic splay-bend pattern in the helix, which couples flexoelectrically to the field. By using a small concentration of photoreactive liquid crystal monomer sless than 5 wt. %d and selecting the illumination conditions, we were able to create a nonuniform polymeric network in the liquid crystal bulk slocalized essentially at both substrate surfacesd which stabilized efficiently the amplitude and the phase modulation modes of the device. This presentation will discuss the possible applications of the fast electro-optic effects based on bimesogenic nematics and their cholesteric mixtures. [1]. R. B. Meyer, “Piezoelectric effects in liquid crystals,” Phys. Rev. Lett., 22, 918 (1969). [2]. J. S. Patel, and R. B. Meyer, “Flexoelectric electro-optics of a cholesteric liquid-crystal,” Phys. Rev. Lett., 58, 1538-1540 (1987). [3]. C.-C. Chang, L.-C. Chien and R. B. Meyer, “Piezoelectric Effects in Cholesteric Elastomer Gels,” Phys. Rev. E., 55, 534 (1997). [4]. R. Barberi, M. Giocondo, J. Li et al., “Fast bistable nematic display with grey scale,” Appl. Phys. Lett., 71, 3495-3497 (1997). [5]. I. Dozov, M. Nobili, and G. Durand, “Fast bistable nematic display using monostable surface switching,” Appl. Phys. Lett., 70, 1179-1181 (1997). [6]. V. P. Panov, M. Nagaraj, J. K. Vij et al., “Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic Constant,” Phys. Rev. Lett., 105, 167801-1-4 (2010). [7]. V. Borshch, Y. K. Kim, J. Xiang et al., “Nematic twist-bend phase with nanoscale modulation of molecular orientation,” Nat. Commun., 4, 2635 (2013). [8]. P. A. Henderson, and C. T. Imrie, “Methylene-linked liquid crystal dimers and the twist-bend nematic phase,” Liq. Cryst., 38, 1407-1414 (2011). [9]. S. H. Kim, L.-C. Chien and L. Komitov, “Short pitch cholesteric electro-optical device stabilized by nonuniform polymer network,” Appl. Phys. Lett., 86, 161118 (2005). [10]. A. Varanytsia and L.-C. Chien, “Giant Flexoelectro-optic effect with liquid crystal dimer CB7CB,” Sci. Rep. 7, 41333 (2017).

 

We investigated the dielectric heating effect in a cholesteric liquid crystal cell with negative dielectric anisotropy. Our results indicated that temperature variations of the cell under voltage applied are attributable to the pseudo-dielectric relaxation due to the finite conductivity of the ITO and significant capacitance of the cell.

 

We demonstrate a new technology to control optical transmission and achieve multi-function(by tint or haze-control). Using dye-doped cholesteric liquid crystal to generate tristable state: transparent (uniform lying helix), dark–clear (planar), and dark–scattering (focal conic) states, without energy conservation.

 

We show that polymeric microwells made by direct laser writing can significantly 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.