Liquid Crystalline Blue Phases Research Articles

Programmable orientation of blue phase soft photonic crystal

Understanding the structure formation and its underlying physical mechanism is a fundamental topic in condensed matter systems, with both academic and practical implications. Soft matter is playing a remarkable role in current era of information explosion, demonstrating enormous potential in integrated functional photonics. As unique soft photonic crystals with cubic symmetries, not only liquid crystalline blue phases (BPs) have circularly polarized selective reflection and ultra-fast electro-optical response, but also their three-dimensional photonic structures increase degrees-of-freedom for multiplexed optical modulation. In the thriving field of soft-matter-based photonics, precise and programmable engineering of BP crystal orientation is of vital importance for planar optical elements, which remains a challenging task due to the complexity of the nucleation process as well as the interaction between the BP building blocks and the boundary conditions. Aiming to gain a comprehensive understanding of how to tailor the orientation of BP crystals for the photonic applications of next generation, here we discuss the solutions for uniformity improvement and orientation control of BP crystals, about which a few of examples in combination with the underlying mechanisms are explained. In addition, the remaining challenges and the efforts that are expected are also reviewed. We expect this work provides a deeper understanding of phase transitions and resulting structures in soft crystals, which may open encouraging perspectives for their applications in photonics, biosensing, interfacial, and chemical engineering.

Electro-Optic Kerr Response in Optically Isotropic Liquid Crystal Phases

The results of an experimental investigation of the temperature and wavelength dependence of the Kerr constant (K) of mixtures with an increasing amount of chiral dopant in an isotropic liquid crystal phase are reported. The material was composed of a nematic liquid crystal (5CB) and a chiral dopant (CE2), which formed non-polymer-stabilized liquid crystalline blue phases with an exceptionally large value of K∼2 × 10−9 mV−2. The measurements were performed on liquid and blue phases at several concentrations covering a range of temperatures and using three wavelengths: 532 nm, 589 nm and 633 nm. The work focused on changes caused by concentration and their impact on the increase in the value of K, and it was found that in the case of the 5CB/CE2 mixture these changes were significant and quite systematic with temperature and wavelength. It is shown that the dispersion relation based on the single-band birefringence model described K well in isotropic liquid crystal phases at all of the measured concentrations. In an isotropic fluid, both temperature-dependent parameters in the dispersion relation had a simple linear form and, therefore, the K-surface could be described by only four constants. In the blue phase, the expression reproducing the temperature variation of K depended on concentration, which could vary from being almost linear to quasi-linear and could be represented well by an inverse exponential analytic expression.

Michael Addition Inducing Self-Assembly to Construct Mechanochromic BP Film.

Liquid crystalline blue phase (BP) with 3D cubic nanostructure has attracted much interest in the fields of photonic crystals due to their unique optical properties and the ability to control the flow of light. However, there remains a challenge for simultaneously achieving self-assembly and mechanochromic response of soft 3D cubic nanostructures. Herein, a scalable strategy for the preparation of soft 3D cubic nanostructured films using oligomerization of the Michael addition reaction, which can induce the assembly of double-twisted cylinders for collective replication, remodeling, recombination, and growth, with a phase transition from BPII to BPI, and to chiral nematic phase, is presented. The prepared BP patterns can be obtained by Michael addition oligomerization reaction and composite mask photopolymerization, which present distinct mechanochromic sensitive due to patterns derived from different BP state, and the pattern can be reversibly erased and recurred by mechanical force and temperature. The average domain size of BPII prepared using this strategy can achieve 96µm, which is 2.5 times larger than that obtained using the conventional cooling approach. This work provides new insights into the self-assembly and selective chemochromism of functional materials and devices.

Synthesis of Thiophene-Based Derivatives and the Effects of Their Molecular Structure on the Mesomorphic Behavior and Temperature Range of Liquid-Crystalline Blue Phases

The development of blue-phase liquid crystal (BPLC) materials with a wide temperature range is of great significance for practical applications in the optoelectronic field. In the study, bent-core derivatives with a 3-hexyl-2,5-disubstituted thiophene central ring in the λ-shaped molecular structure were designed and synthesized. Their mesomorphic behavior and effect on the blue-phase (BP) temperature range were investigated. Interestingly, a BP was achieved both during the heating and cooling processes by doping with a proper concentration of chiral compound into the thiophene bent-shaped molecule with high rigidity, while derivatives with fluorine atom substitution only exhibited cholesteric phase no matter how many chiral compounds were added. This result proved that BP is highly sensitive to the molecular structures of bent-shaped molecules. Moreover, the BP temperature range was broadened when adding these molecules into a BPLC host, which thus improved the BP temperature range from the initial value, no more than 4 °C, to as much as 24 °C. The experimental phenomena were reasonably explained through molecular simulation calculations. The study may provide some experimental basis and theoretical guidance for the design of novel bent-shaped molecules and BPLC material with a wide temperature range.

Ultrastable liquid crystalline blue phase from molecular synergistic self-assembly

Fabricating functional materials via molecular self-assembly is a promising approach, and precisely controlling the molecular building blocks of nanostructures in the self-assembly process is an essential and challenging task. Blue phase liquid crystals are fascinating self-assembled three-dimensional nanomaterials because of their potential information displays and tuneable photonic applications. However, one of the main obstacles to their applications is their narrow temperature range of a few degrees centigrade, although many prior studies have broadened it to tens via molecular design. In this work, a series of tailored uniaxial rodlike mesogens disfavouring the formation of blue phases are introduced into a blue phase system comprising biaxial dimeric mesogens, a blue phase is observed continuously over a temperature range of 280 °C, and the range remains over 132.0 °C after excluding the frozen glassy state. The findings show that the molecular synergistic self-assembly behavior of biaxial and uniaxial mesogens may play a crucial role in achieving the ultrastable three-dimensional nanostructure of blue phases.

Topological transitions in an oscillatory driven liquid crystal cell

Matter under different equilibrium conditions of pressure and temperature exhibits different states such as solid, liquid, gas, and plasma. Exotic states of matter, such as Bose–Einstein condensates, superfluidity, chiral magnets, superconductivity, and liquid crystalline blue phases are observed in thermodynamic equilibrium. Rather than being a result of an aggregation of matter, their emergence is due to a change of a topological state of the system. These topological states can persist out of thermodynamics equilibrium. Here we investigate topological states of matter in a system with injection and dissipation of energy by means of oscillatory forcing. In an experiment involving a liquid crystal cell under the influence of a low-frequency oscillatory electric field, we observe a transition from a non-vortex state to a state in which vortices persist, topological transition. Depending on the period and the type of the forcing, the vortices self-organise, forming square lattices, glassy states, and disordered vortex structures. The bifurcation diagram is characterised experimentally. A continuous topological transition is observed for the sawtooth and square forcings. The scenario changes dramatically for sinusoidal forcing where the topological transition is discontinuous, which is accompanied by serial transitions between square and glassy vortex lattices. Based on a stochastic amplitude equation, we recognise the origin of the transition as the balance between stochastic creation and deterministic annihilation of vortices. Numerical simulations show topological transitions and the emergence of square vortex lattice. Our results show that the matter maintained out of equilibrium by means of the temporal modulation of parameters can exhibit exotic states.

Origin and structure of liquid crystalline Blue Phase III

We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral ellipsoidal molecules, which spontaneously exhibits Blue Phase III (BPIII), considering coarse-grained attractive-repulsive pair interaction appropriate for anisotropic liquid crystal mesogens. We have observed that suitable selection of chiral and dipolar strengths not only gives rise to thermodynamically stable BPIII but novel Smectic and Bilayered BPIII as well. Further, we have demonstrated that the occurrence of BPIII and its layered counterparts depend crucially on molecular elongation.

Reversible On–Off of Chirality and Anisotropy in Patterned Coexistence of Achiral‐Anisotropic and Chiral‐Isotropic Soft Materials

AbstractAchieving a coexistence of two or multiple phases of soft matters via a delicate trade‐off of free energy and long‐range order with one another has been inspiring abundant interest on fundamental sciences and engineering. In this work, a stable coexistence of the optically achiral‐anisotropic liquid crystalline nematic phase and the optically chiral‐isotropic liquid crystalline blue phase is proposed and demonstrated, with their distribution tailored in a micro‐pattern by the developed localized micro‐regional polymer templating technique. Such a stable patterned coexistence of the two different phases with a distinct molecular arrangement, optical chirality, and anisotropy is achieved depending on a delicate matching of the elastic energy on the interface between liquid crystals and polymer networks. In contrast to the majority of soft coexistence systems, a specific dynamic and reversible on–off response of chirality and anisotropy is observed in such a system driven by an electric field. The structure of patterned coexistence system in the presence and absence of external stimulation is explored by microscopy and optical technique, and furthermore, the prospective photonic applications are demonstrated. This investigation indicates another category of functional soft material with fantastic adaptive characteristics for application in optics, electronics, interface physics, and chemistry.

Polymer‐Stabilized Monodomain Blue Phase Diffraction Grating

AbstractThe structural beauty of liquid crystalline blue phases is attested not only by their colorful optical micrographic textures but also by optical isotropy. More importantly, the homogeneity of the structures influences greatly to the electro‐optic properties. In this work, how the lattice orientation in polymer‐stabilized blue phase liquid crystal (PS‐BPLC) diffraction grating affects phase‐modulated diffraction efficiency is elaborated. A well‐arranged monodomain structure of blue phase is achieved and its diffraction capability is compared with multidomain PS‐BPLC. The diffraction efficiency in the zeroth order of monodomain PS‐BPLC is improved by 9% compared to that of multidomain structure. In addition, both driving and threshold voltages in monodomain PS‐BPLC are decreased by 29% and 30%, respectively, compared to those in multidomain PS‐BPLC owing to the regular arrangement of cubic lattices that give rise to increase in the coherence length and unified response in molecular reorientation under electric fields. Furthermore, the monodomain PS‐BPLC shows an efficient polarization conversion of linear polarization into circular polarization. It is believed that the device exhibits great potential to be used as a polarization converter or beam steering devices.

Nanoparticle-Stabilized Lattices of Topological Defects in Liquid Crystals

We present a review of nanoparticle (NP) stabilized lattices of topological defects (TDs) in liquid crystals (LCs). We focus on conditions for which chiral liquid-crystalline blue phases and twist-grain boundary A phases might be stable in bulk LCs. These phases exhibit lattices of disclinations and dislocations corresponding to line TDs in orientational and translational LC order, respectively. NPs of appropriate size and surface coating can assemble in the cores of defects and stabilize metastable or increase the temperature range of already stable lattices of TDs. The stabilization is achieved by the universal defect core replacement and adaptive defect core targeting mechanisms. Representative experiments revealing these phenomena and potential applications are discussed.

Photonic Shape Memory Polymer Based on Liquid Crystalline Blue Phase Films.

Photonic shape memory (SM) polymers based on liquid crystalline blue phase (BP) films have been fabricated by self-assembly and subsequent photopolymerization of liquid-crystal mixtures. These freestanding BP films exhibit narrow photonic band gaps and high reflectivity in the visible wavelength range. Multiple blue-shift colors are achieved by SM programming process at different mechanical pressures. The blue-shift colors can be attributed to a decrease of effective BP pitch along the viewing direction caused by the compressed deformation of the BP films, which are confirmed by a three-dimensional interometric profile. The deformed BP films can recover to their original shapes and reflecting colors by heating the polymer films to temperatures above the glass-transition temperature. Quantitative relationships between the shape change and optical response are established for understanding this SM effect. What is more, the temporary photonic patterns can be reversibly written and erased for dozens of cycles without apparent degradation, making these freestanding BP films appealing as rewritable photonic papers and optical sensors.

Liquid crystalline blue phase materials with three-dimensional nanostructures

This review presents up-to-date important progress in the field of liquid crystalline blue phase (BP) materials.

Development of a liquid crystal laser using a simple cubic liquid crystalline blue phase platform.

A liquid crystal laser using a polymer-stabilized simple cubic blue phase (BPII) platform has been scarcely reported because the polymer stabilization of a BPII is relatively difficult compared to that of a body-centered-cubic BP (BPI). In this study, we succeeded in fabricating a dye-doped polymer-stabilized BPII laser with wide operating-temperature ranges over 15 °C including room temperature. A narrow and sharp single laser peak with a full width at half maximum of approximately 2 nm was derived from the photonic band edge effect of the BPII-distributed feedback optical resonator. As a result, the laser emission was a circularly polarized light, which matched the chirality of the proposed pure BPII.

Printable photonic polymer coating based on a monodomain blue phase liquid crystal network

In this paper, a printable photonic polymer coating was fabricated from a monodomain liquid crystalline blue phase network.

Correction: Wide-angle lasing from photonic crystal nanostructures of a liquid-crystalline blue phase

Correction for ‘Wide-angle lasing from photonic crystal nanostructures of a liquid-crystalline blue phase’ by Guan-Yu Zhuo et al., J. Mater. Chem. C, 2019, 7, 6433–6439.

The influence of orienting layers on blue phase liquid crystals in rectangular geometries

In this paper, the influence of homeotropic and homogeneous orienting layers is presented in a cell filled with chiral nematic liquid crystals stabilized in a blue phase. The change of selective Bragg reflection from red to blue light was observed for homogeneous layers in rectangular geometries. The growth of blue phase crystals domains in a glass cell as well an influence of temperature and the electric field on such a structure, are also presented. Full Text: PDF ReferencesF. Reinitzer, Beitrage zur Kenntniss des Cholestherins, Monatsh Chem. 9, 421-441, (1888). CrossRef J. Yan, M. Jiao, L. Rao, and S.-T. Wu, "Direct measurement of electric-field-induced birefringence in a polymer-stabilized blue-phase liquid crystal composite", Opt. Express 18, 11450-11455 (2010) CrossRef Y. Chen, D. Xu, S.-T. Wu, S.-i. Yamamoto, Y. Haseba, "A low voltage and submillisecond-response polymer-stabilized blue phase liquid crystal", Appl. Phys. Lett. 102, 141116 (2013) CrossRef Y. Huang, H. Chen, G. Tan, H. Tobata, S. Yamamoto, E. Okabe, Y.-F. Lan, C.-Y. Tsai, and S.-T. Wu, "Optimized blue-phase liquid crystal for field-sequential-color displays", Opt. Mater. Express 7, 641-650 (2017) CrossRef V. Sridurai, M. Mathews, C. V. Yelamaggad, G. G. Nair, "Electrically Tunable Soft Photonic Gel Formed by Blue Phase Liquid Crystal for Switchable Color-Reflecting Mirror", ACS Appl. Mater. Interfaces, 9 (45), 39569-39575 (2017) CrossRef E. Oton, E. Netter, T. Nakano, Y. D.-Katayama, F. Inoue, "Monodomain Blue Phase Liquid Crystal Layers for Phase Modulation", Sci. Rep. vol.7, 44575 (2017) CrossRef Q. Liu, D. Luo, X. Zhang, S. Li, Z. Tian, "Refractive index and absorption coefficient of blue phase liquid crystal in terahertz band", Liq. Cryst., Vol. 44, No. 2, pp. 348-354 (2017) CrossRef Y. Li, Y. Liu, Q. Li, S.-T. Wu, "Polarization independent blue-phase liquid crystal cylindrical lens with a resistive film", Appl. Opt., Vol. 51, No. 14, pp. 2568-2572 (2012) CrossRef M. M. Sala-Tefelska, K. Orzechowski M. Sierakowski, A. Siarkowska, T.R. Woliński, O. Strzeżysz, P. Kula, "Influence of cylindrical geometry and alignment layers on the growth process and selective reflection of blue phase domains", Opt. Mater. 75, 211-215, (2018) CrossRef H. Claus, O. Willekens, O. Chojnowska, R. Dąbrowski, J. Beeckman, K. Neyts, "Inducing monodomain blue phase liquid crystals by long-lasting voltage application during temperature variation", Liq. Cryst. 43 (5), 688-693, (2016) CrossRef M. Takahashi, T. Ohkawa, H. Yoshida, J. Fukuda, H. Kikuchi, M. Ozaki, "Orientation of liquid crystalline blue phases on unidirectionally orienting surfaces", J. Phys. D: Appl. Phys. 51 (10), 104003 (2018) CrossRef P. Joshi, X. Shang, J. De Smet, E. Islamai, D. Cuypers, G. Van Steenberge, S. Van Vlierberghe, P. Dubruel, H. De Smet, "On the effect of alignment layers on blue phase liquid crystals", Appl. Phys. Lett. 106, 101105 (2015) CrossRef K. Orzechowski, M.W. Sierakowski, M. Sala-Tefelska, P. Joshi, T.R. Woliński, H.D. Smet, "Polarization properties of cubic blue phases of a cholesteric liquid crystal", Opt. Mater. 69, 259-264 (2017) CrossRef P.-J. Chen, M. Chen, S.-Y. Ni, H.-S. Chen, Y.-H. Lin, "Influence of alignment layers on crystal growth of polymer-stabilized blue phase liquid crystals", pt. Mater. Express 6, 1003-1010 (2016) CrossRef CrossRef

Large Electro‐Optic Kerr Effect in Ionic Liquid Crystals: Connecting Features of Liquid Crystals and Polyelectrolytes

The electro-optic Kerr effect in simple dipolar fluids such as nitrobenzene has been widely applied in electro-optical phase modulators and light shutters. In 2005, the discovery of the large Kerr effect in liquid-crystalline blue phases (Y. Hisakado et al., Adv. Mater. 2005, 17, 96-98.) gave new directions to the search for advanced Kerr effect materials. Even though the Kerr effect is present in all transparent and optically isotropic media, it is well known that the effect can be anomalously large in complex fluids, namely in the isotropic phase of liquid crystals or in polyelectrolyte solutions. Herein, it is shown that the Kerr effect in the isotropic phase of ionic liquid crystals combines the effective counterion polarization mechanism found in polyelectrolytes and the unique pretransitional growth of the Kerr constant found in the isotropic phase of nematic liquid crystals. Maximum Kerr constants in the order of several 10-11 m V-2 (ten times higher than the Kerr constant of the toxic nitrobenzene and less temperature sensitive than Kerr constants of nematic liquid crystals) make ionic liquid crystals attractive as new class of functional materials in low-speed Kerr effect applications.

Orientation of liquid crystalline blue phases on unidirectionally orienting surfaces

Liquid crystalline cholesteric blue phases (BPs) continue to attract interest due to their fast response times and quasi-polarization-independent phase modulation capabilities. Various approaches have recently been proposed to control the crystal orientation of BPs on substrates; however, their basic orientation properties on standard, unidirectionally orienting alignment layers have not been investigated in detail. Through analysis of the azimuthal orientation of Kossel diagrams, we study the 3D crystal orientation of a BP material—with a phase sequence of cholesteric, BP I, and BP II—on unidirectionally orienting surfaces prepared using two methods: rubbing and photoalignment. BP II grown from the isotropic phase is sensitive to surface conditions, with different crystal planes orienting on the two substrates. On the other hand, strong thermal hysteresis is observed in BPs grown through a different liquid crystal phase, implying that the preceding structure determines the orientation. More specifically, the BP II–I transition is accompanied by a rotation of the crystal such that the crystal direction defined by certain low-value Miller indices transform into different directions, and within the allowed rotations, different azimuthal configurations are obtained in the same cell depending on the thermal process. Our findings demonstrate that, for the alignment control of BPs, the thermal process is as important as the properties of the alignment layer.

The temperature range and optical properties of the liquid crystalline blue phase in inverse opal structures

A liquid crystal device was developed by infiltrating a blue phase liquid crystal (BPLC) in three-dimensional SiO2 inverse opal (IOP) structures, of which the BP temperature range and electro-optical performance were investigated.

Fabrication of the liquid crystalline periodic waveguiding structures by means of the photo-polymerization process

Photonic structures in a form of the waveguide channels, with periodic spatial changes in refractive index in the wavelength scale, are typically manufactured based on well-developed silica and gallium arsenide technology [1], as well as with use of the high-precision lithography. The main disadvantage related to practical application of such devices is that their optical properties cannot be altered after fabrication. Due to this fact, liquid crystalline periodic waveguiding structures, manufactured with use of the photo-polymerization process, have been proposed in this work. Importantly, propagational characteristic of such photonic structures can be easily adjusted during fabrication procedure, and then may be also dynamically tuned by e.g. applied external voltage, as presented in this communication. Full Text: PDF ReferencesM.J. Ablowitz, Z.H. Musslimani, "Discrete spatial solitons in a diffraction-managed nonlinear waveguide array: a unified approach", Physica D: Nonlinear Phenomena 184(1), 276 (2003). CrossRef L. Vicari, Optical applications of liquid crystals, CRC press, 2016. CrossRef J. Yan, S.-T. Wu, "Effect of Polymer Concentration and Composition on Blue Phase Liquid Crystals", J. Display Technol. 7, 9 (2011). CrossRef J. Schirmer et al., "Birefringence and Refractive Indices Dispersion of Different Liquid Crystalline Structures", Mol. Cryst. Liquid Cryst. 307, 17 (1997). CrossRef D. Xu et al., "Blue phase liquid crystals stabilized by linear photo-polymerization", Appl. Phys. Lett. 105, 8 (2014). CrossRef I. Dierking et al., "Stabilising liquid crystalline Blue Phases", Soft Matter 8, 4355 (2012). CrossRef K. Kang, L.C. Chien, S. Sprunt, "Polymer-stabilized cholesteric liquid crystal microgratings: a comparison of polymer network formation and electro-optic properties for mesogenic and non-mesogenic monomers", Liquid Crystals 29, 9 (2002). CrossRef K.A. Rutkowska, M. Chychłowski, U.A. Laudyn, "Polymer-stabilized periodic waveguiding structures in liquid crystalline materials", Proc. SPIE 10325 (2017). CrossRef