Strongly Chiral Liquid Crystals in Nanoemulsions Yang, Yu; Palacio‐Betancur, Viviana; Wang, Xin ...
Small (Weinheim an der Bergstrasse, Germany),
01/2022, Letnik:
18, Številka:
10
Journal Article
Recenzirano
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We report Liquid crystal (LC) emulsions represent a class of confined soft matter that exhibit exotic internal organizations and size-dependent properties, including responses to chemical and ...physical stimuli. Past studies have explored micrometer-scale LC emulsion droplets but little is known about LC ordering within submicrometer-sized droplets. This paper reports experiments and simulations that unmask the consequences of confinement in nanoemulsions on strongly chiral LCs that form bulk cholesteric and blue phases (BPs). A method based on light scattering is developed to characterize phase transitions of LCs within the nanodroplets. For droplets with a radius to the pitch ratio (Rv/p0) as small as 2/3, the BP-to-cholesteric transition is substantially suppressed, leading to a threefold increase of the BP temperature interval relative to bulk behavior. Complementary simulations align with experimental findings and reveal the dominant role of chiral elastic energy. For Rv/p0 ≈ to 1/3, a single LC phase forms below the clearing point, with simulations revealing the new configuration to contain a τ-1/2 disclination that extends across the nanodroplet. These findings are discussed in the context of mechanisms by which polymer networks stabilize BPs and, more broadly, for the design of nanoconfined soft matter.
Carbon nanotube (CNT)-doped polymer-stabilised blue phase (PSBP) liquid crystal cells driven by an in-plane field are fabricated. Their electro-optical properties are investigated for both ...single-wall and multiwall CNT dopants. A small amount of CNT dopants in PSBP liquid crystals leads to broadening the blue phase temperature range over 42°C and stabilising the reflection wavelength against temperature changes. A lower Kerr constant and threshold voltage are obtained for a higher CNT concentration. Higher CNT concentrations lead to an increase in the elastic constant; therefore, the rise time of CNT-doped PSBP liquid crystal cells increases and decay time decreases.
Abstract This study investigates the influence of Grandjean–Cano disclinations on the cholesteric-blue phase I (Ch-BPI) phase transition, revealing the pivotal role of defects in the phase transition ...of liquid crystals (LCs). We prepared the disclinations by wedge cells or parallel cells with an alignment pattern and demonstrated that the disclinations induce a phase transition in Ch-BPI. Furthermore, we demonstrated the control of the BPI appearance areas by utilizing this property. This defect-induced transition technique not only provides a novel method for controlling BPI orientation, but also offers insights into soft material crystal growth, suggesting potential applications in new BPLC-based device development.
Blue-phase liquid crystal droplets Martínez-González, José A.; Zhou, Ye; Rahimi, Mohammad ...
Proceedings of the National Academy of Sciences - PNAS,
10/2015, Letnik:
112, Številka:
43
Journal Article
Blue phase liquid crystals (BPLCs) are chiral mesophases with 3D order, which makes them a promising template for doping nanoparticles (NPs), yielding tunable nanomaterials attractive for microlasers ...and numerous microsensor applications. However, doping NPs to BPLCs causes BP lattice extension, which translates to elongation of operating wavelengths of light reflection. Here, it is demonstrated that small (2.4 nm diameter) achiral gold (Au) NPs decorated with designed LC-like ligands can enhance the chiral twist of BPLCs (i.e., reduce cell size of the single BP unit up to ∼14% and ∼7% for BPI and BPII, respectively), translating to a blue-shift of Bragg reflection. Doping NPs also significantly increases the thermal stability of BPs from 5.5 °C (for undoped BPLC) up to 22.8 °C (for doped BPLC). In line with our expectations, both effects are saturated, and their magnitude depends on the concentration of investigated nanodopants as well the BP phase type. Our research highlights the critical role of functionalization of Au NPs on the phase sequence of BPLCs. We show that inappropriate selection of surface ligands can destabilize BPs. Our BPLC and Au NPs are photochemically stable and exhibit great miscibility, preventing NP aggregation in the BPLC matrix over the long term. We believe that our findings will improve the fabrication of advanced nanomaterials into 3D periodic soft photonic structures.
Blue-phase liquid crystal droplets Martínez-González, José A.; Zhou, Ye; Rahimi, Mohammad ...
Proceedings of the National Academy of Sciences - PNAS,
10/2015, Letnik:
112, Številka:
43
Journal Article
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Blue phases of liquid crystals represent unique ordered states of matter in which arrays of defects are organized into striking patterns. Most studies of blue phases to date have focused on bulk ...properties. In this work, we present a systematic study of blue phases confined into spherical droplets. It is found that, in addition to the so-called blue phases I and II, several new morphologies arise under confinement, with a complexity that increases with the chirality of the medium and with a nature that can be altered by surface anchoring. Through a combination of simulations and experiments, it is also found that one can control the wavelength at which blue-phase droplets absorb light by manipulating either their size or the strength of the anchoring, thereby providing a liquid–state analog of nanoparticles, where dimensions are used to control absorbance or emission. The results presented in this work also suggest that there are conditions where confinement increases the range of stability of blue phases, thereby providing intriguing prospects for applications
Liquid crystals are important components of optical technologies. Cuboidal crystals consisting of chiral liquid crystals–the so-called blue phases (BPs), are of particular interest due to their ...crystalline structures and fast response times, but it is critical that control be gained over their phase behavior as well as the underlying dislocations and grain boundaries that arise in such systems. Blue phases exhibit cubic crystalline symmetries with lattice parameters in the 100 nm range and a network of disclination lines that can be polymerized to widen the range of temperatures over which they occur. Here, we introduce the concept of strain-controlled polymerization of BPs under confinement, which enables formation of strain-correlated stabilized morphologies that, under some circumstances, can adopt perfect single-crystal monodomain structures and undergo reversible crystal-to-crystal transformations, even if their disclination lines are polymerized. We have used super-resolution laser confocal microscopy to reveal the periodic structure and the lattice planes of the strain and polymerization stabilized BPs in 3D real space. Our experimental observations are supported and interpreted by relying on theory and computational simulations in terms of a free energy functional for a tensorial order parameter. Simulations are used to determine the orientation of the lattice planes unambiguously. The findings presented here offer opportunities for engineering optical devices based on single-crystal, polymer-stabilized BPs whose inherent liquid nature, fast dynamics, and long-range crystalline order can be fully exploited.
The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review ...these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.
Strongly Chiral Liquid Crystals in Nanoemulsions Yang, Yu; Palacio‐Betancur, Viviana; Wang, Xin ...
Small (Weinheim an der Bergstrasse, Germany),
03/2022, Letnik:
18, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Liquid crystal (LC) emulsions represent a class of confined soft matter that exhibit exotic internal organizations and size‐dependent properties, including responses to chemical and physical stimuli. ...Past studies have explored micrometer‐scale LC emulsion droplets but little is known about LC ordering within submicrometer‐sized droplets. This paper reports experiments and simulations that unmask the consequences of confinement in nanoemulsions on strongly chiral LCs that form bulk cholesteric and blue phases (BPs). A method based on light scattering is developed to characterize phase transitions of LCs within the nanodroplets. For droplets with a radius to the pitch ratio (Rv/p0) as small as 2/3, the BP‐to‐cholesteric transition is substantially suppressed, leading to a threefold increase of the BP temperature interval relative to bulk behavior. Complementary simulations align with experimental findings and reveal the dominant role of chiral elastic energy. For Rv/p0 ≈ 1/3, a single LC phase forms below the clearing point, with simulations revealing the new configuration to contain a τ−1/2 disclination that extends across the nanodroplet. These findings are discussed in the context of mechanisms by which polymer networks stabilize BPs and, more broadly, for the design of nanoconfined soft matter.
A method based on light scattering is developed to characterize the phase behavior of chiral liquid crystals confined in nanoemulsion droplets. The study reveals that confinement in nanodroplets leads to the suppression of the cholesteric‐to‐blue phase transition temperature, and the emergence of an exotic phase different from the bulk state.
A blue phase with a broad temperature range of about 23.0 °C is easily achieved in a hydrogen‐bonded self‐assembled complex of chiral fluoro‐substituted benzoic acid and pyridine derivative. The ...success in extending the temperature of blue phase indicates that the hydrogen‐bonded self‐assembly is a promising new approach to broaden the temperature range of blue phases and to investigate the mystery of blue phases.
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