Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size ...grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Helical nanofilament (HNF) phases form as a result of an intralayer mismatch between top and bottom molecular halves in bent‐core liquid crystals (BC‐LCs) that is relieved by local saddle‐splay ...geometry. HNFs are immensely attractive for photovoltaic and chiral separation applications and as templates for the chiral spatial assembly of guest molecules. Here, the synthesis and characterization of two unichiral BC‐LCs and one racemic mixture with tris‐biphenyl‐diester cores featuring chiral (R,R) and (S,S) or racemic 2‐octyloxy aliphatic side chains are presented. In comparison to the achiral compound with linear side chains forming an intralayer modulated HNF phase (HNFmod), synchrotron small angle X‐ray diffraction indicates that the unichiral derivatives form a dual modulated HNF phase with intra‐ as well as interlayer modulations (HNFmod2) suggesting a columnar local structure of the nanofilaments. Transmission electron microscopy and circular dichroism spectropolarimetry confirm that the unichiral materials exclusively form homochiral HNFs with a twist sense‐matching secondary twist. A contact preparation provides the first example of two identical chiral liquid crystal phases only differing in their handedness that do not mix and form an achiral liquid crystal phase with an entirely different structure in the contact zone.
Helical nanofilaments twist in sync forming a dual modulated, homochiral helical nanofilament phase, but only when the constituent molecules are unichiral. Left‐handed nanofilaments form a left‐handed, right‐handed nanofilaments a right‐handed secondary twist. The two phases with opposite handedness do not mix by forming a chiral conglomerate, as their achiral molecular counterparts, but rather induce a short correlated crystalline ribbon phase.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The recently discovered ferroelectric nematic (N_{F}) liquid crystals (LC) have been reported to show an extraordinarily large value of the real part of the dielectric constant (ϵ^{'}>10^{3}) at low ...frequencies. However, it was argued by Clark et al. in Phys. Rev. Res. 6, 013195 (2024)PPRHAI2643-156410.1103/PhysRevResearch.6.013195 that what was measured was the capacitance of the insulating layer at LC or electrode surface and not that of the liquid crystal. Here we describe the results of dielectric spectroscopy measurements of an N_{F} material in cells with variable thickness of the insulating layers. Our measurements quantitatively verify the model by Clark et al. Additionally, our measurements in cells with bare conducting indium tin oxide surface provide a crude estimate of ϵ_{⊥}∼10^{2} in the N_{F} phase.The recently discovered ferroelectric nematic (N_{F}) liquid crystals (LC) have been reported to show an extraordinarily large value of the real part of the dielectric constant (ϵ^{'}>10^{3}) at low frequencies. However, it was argued by Clark et al. in Phys. Rev. Res. 6, 013195 (2024)PPRHAI2643-156410.1103/PhysRevResearch.6.013195 that what was measured was the capacitance of the insulating layer at LC or electrode surface and not that of the liquid crystal. Here we describe the results of dielectric spectroscopy measurements of an N_{F} material in cells with variable thickness of the insulating layers. Our measurements quantitatively verify the model by Clark et al. Additionally, our measurements in cells with bare conducting indium tin oxide surface provide a crude estimate of ϵ_{⊥}∼10^{2} in the N_{F} phase.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Liquid crystal (LC)-based biological sensors permit the study of aqueous biological samples without the need for the labeling of biological species with fluorescent dyes (which can be laborious and ...change the properties of the biological sample under study). To date, studies of LC-based biosensors have explored only a narrow range of the liquid crystal/alignment layer combinations essential to their operation. Here, we report a study of the role of LC elastic constants and the surface anchoring energy in determining the sensitivity of LC-based biosensors. By investigating a mixture of rod-shape and bent-shape mesogens, and three different alignment layers, we were able to widen the useful detection range of a LC-based sensor by providing an almost-linear mapping of effective birefringence with anionic surfactant concentrations between 0.05 mM and 1 mM (model target analyte). These studies pave the way for optimization of LC-based biosensors and reveal the importance of the choice of both the LC material and the alignment layer in determining sensor properties.
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IJS, KILJ, NUK, PNG, UL, UM
Preparation and low voltage induced bending (converse flexoelectricity) of crosslinked poly(ethylene glycol) diacrylate (PEGDA), modified with thiosiloxane (TS) and ionic liquid ...(1‐hexyl‐3‐methylimidazolium hexafluorophosphate) (IL) are reported. In between 2µm PEDOT:PSS electrodes at 1 V, it provides durable (95% retention under 5000 cycles) and relatively fast (2 s switching time) actuation with the second largest strain observed so far in ionic electro‐active polymers (iEAPs). In between 40 nm gold electrodes under 8 V DC voltage, the film can be completely curled up (270° bending angle) with 6% strain that, to the best of the knowledge, is unpreceded among iEAPs. These results render great potential for the TS/PEGDA/IL based electro‐active actuators for soft robotic applications.
Low voltage operation of poly(ethylene glycol) diacrylate based ionic electroactive polymer actuator is presented. In between PEDOT:PSS electrodes, it provides the second largest strain observed in ionic electro‐active polymers (iEAPs). In between gold electrodes, the film can be completely curled up, in a way that is unpreceded among iEAPs. These results show great potential for TS/PEGDA/IL based electro‐active actuators.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Liquid Gallium
In article number 2104807, Antal Jákli, Metin Sitti, and co‐workers observe a Schlieren texture in a supercooled liquid gallium film on a glass surface with an open‐air boundary. The ...thin liquid film visualized with a circularly polarized light using reflective polarized microscopy shows two brush defects due to the presence of only 1/2‐strength defects. The boundary layer tends to align the liquid crystal director parallel to the substrate in a degenerate planar condition.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Tunable optical lenses are in great demand in modern technologies ranging from augmented and virtual reality to sensing and detection. In this work, electrically tunable microlenses based on a ...polymer‐stabilized chiral ferroelectric nematic liquid crystal are described. The power of the lens can be quickly (within 5 ms) varied by ≈500 diopters by ramping an in‐plane electric field from 0 to 2.5 V µm−1. Importantly, within this relatively low‐amplitude field range, the lens is optically isotropic; thus, its focal length is independent of the polarization of incoming light. This remarkable performance combines the advantages of electrically tuned isotropic lenses and the field‐controlled shape of the lens, which are unique properties of chiral ferroelectric nematic liquid crystals and have no counterpart in other liquid crystals. The achieved lens performance represents a significant step forward as compared to liquid lenses controlled by electrowetting and opens new possibilities in various applications such as biomimetic optics, security printing, and solar energy concentration.
The electrical field‐induced shape change of polymer‐stabilized chiral ferroelectric nematic microlens arrays at room temperature is illustrated. The liquid crystal‐air interface topography is measured by a Digital Holographic Microscope. The insets show the 3D rendering of the shape. Color coding shows the lens shape remains axially symmetric under in‐plane field. The achieved lens performance represents a significant step forward.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We present quantitative measurements of the optical response of liquid crystal (LC)/polymer composite fiber mats to toluene and acetone vapors. Our analyses in comparison with control measurements of ...pure LC film and polymer fiber mats show that the chemicals can pass through the polymer sheath of the fibers and be absorbed by the LC in the core. This absorption changes the optical properties of the fiber mats which can be used to produce sensitive and reversible detection. The sensitive response at low concentrations of both acetone and toluene demonstrates the feasibility of using these fibers for highly sensitive and specific sensors for volatile organic compound detection.
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•Optical response of flexible fiber mats to chemical vapors was presented.•The mats consisting of liquid crystal/polymer composite were prepared by electrospinning.•Microscopic and macroscopic observations of the response were presented.•Sensing mechanism was proposed and discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Topological defects and defect phases of rigid and flexibly bent-shaped liquid crystals are reviewed with emphasis on how they are affected by the departure of molecular shapes from a simple rod. The ...review discusses defects in bent-core uniaxial and hypothetical biaxial nematics, twist-bend nematic, and various frustrated layered bent-core liquid crystals, such as twist-grain boundary phase, nanoscale helical nanofilament phase, and the so-called B
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textures with helical ribbons.
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