In this review article, we analyze recent progress in the application of liquid crystal-assisted advanced functional materials for sensing biological and chemical analytes. Multiple research groups ...demonstrate substantial interest in liquid crystal (LC) sensing platforms, generating an increasing number of scientific articles. We review trends in implementing LC sensing techniques and identify common problems related to the stability and reliability of the sensing materials as well as to experimental set-ups. Finally, we suggest possible means of bridging scientific findings to viable and attractive LC sensor platforms.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Organic Electrochemical Transistors (OECTs) have the potential to enable fully flexible, low-cost electronics. Here, we demonstrate that OECTs can be combined with ionic liquid crystal elastomers ...(iLCEs) to realise highly sensitive bending sensors. The transfer curve of the iLCE-based OECT shows opposite variation with upward and downward bending representing a directional sensitive strain sensor. The change in the drain current is 4 orders of magnitude larger than the flexo-ionic current. This high sensitivity is due to the OECT that amplifies the flexo-ionic current. iLCE-based OECTs therefore present a new class of curvature sensors that may find applications in soft robotics and biosensing.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
A thermal gradient-induced circular motion of particles placed on ferroelectric nematic liquid crystal sessile drops is demonstrated and explained. Unlike hurricanes and tornadoes that are the prime ...examples for thermal motors and where turbulent flows are apparent, here the texture without tracer particles appears completely steady indicating laminar flow. We provide a simple model showing that the tangential arrangement of the ferroelectric polarization combined with the vertical thermal gradient and the pyroelectricity of the fluid drives the rotation of the tracer particles that become electrically charged in the fluid. These observations provide a fascinating example of the unique nature of fluid ferroelectric liquid crystals.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A homogeneous solution of a low‐molecular‐weight liquid crystal and a polymer spontaneously phase separates during airbrushing to form uniform fibers with a fluid liquid‐crystal core surrounded by a ...solid polymer sheath. This structure forms because it effectively minimizes the interfacial energy of the phase‐separated components while minimizing the elastic energy of the liquid‐crystal core. These fibers incorporate the sensitive stimuli response of liquid crystals while maintaining the structural integrity, flexibility, and large surface‐area‐to‐volume ratios inherent in fibers. We demonstrate the electro‐ and thermo‐optical response of the resulting fibers. They may find use as biological and chemical sensors. The resulting fibers have the potential to shape the future of flexible/wearable electronics and sensors.
Picture perfect: A homogeneous solution of a low‐molecular‐weight liquid crystal and a polymer spontaneously phase separates during airbrushing to form uniform fibers with a fluid liquid‐crystal core surrounded by a solid polymer sheath. These stimuli‐responsive fibers maintain the structural integrity, flexibility, and large surface area inherent in fibers.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Using a photo-responsive dimer exhibiting the transition between nematic (N) and twist-bend nematic (NTB) phases, we prepared spherical cap-shaped droplets on solid substrates exposed to air. The ...internal director structures of these droplets vary depending on the phase and on the imposed boundary conditions. The structural switching between the N and NTB phases was successfully performed either by temperature control or by UV light-irradiation. The N phase is characterized by an extremely small bend elastic constant K3, and surprisingly, we found that the droplet-air interface induces a planar alignment, in contrast to that seen for typical calamitic liquid crystals. As a consequence, the director configuration was stabilized in a structure substantially different from that normally found in conventional nematic liquid crystalline droplets. In the twist-bend nematic droplets characteristic structures with macroscopic length scales were formed, and they were well controlled by the droplet size. These results indicated that a continuum theory is effective in describing the stabilization mechanism of the macroscopic structure even in the twist-bend nematic liquid crystal droplets exhibiting director modulations on a scale of several molecular lengths.
The range of possible morphologies for bent‐core B4 phase liquid crystals has recently expanded from helical nanofilaments (HNFs) and modulated HNFs to dual modulated HNFs, helical microfilaments, ...and heliconical‐layered nanocylinders. These new morphologies are observed when one or both aliphatic side chains contain a chiral center. Here, the following questions are addressed: which of these two chiral centers controls the handedness (helicity) and which morphology of the nanofilaments is formed by bent‐core liquid crystals with tris‐biphenyl diester core flanked by two chiral 2‐octyloxy side chains? The combined results reveal that the longer arm of these nonsymmetric bent‐core liquid crystals controls the handedness of the resulting dual modulated HNFs. These derivatives with opposite configuration of the two chiral side chains now feature twice as large dimensions compared to the homochiral derivatives with identical configuration. These results are supported by density functional theory calculations and stochastic dynamic atomistic simulations, which reveal that the relative difference between the para‐ and meta‐sides of the described series of compounds drives the variation in morphology. Finally, X‐ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) data also uncover the new morphology for B4 phases featuring p2/m symmetry within the filaments and less pronounced crystalline character.
Positioning chiral centers in the aliphatic side chains of asymmetric bent‐core liquid crystals, thereby strategically introducing chiral centers, leads to a new morphology for the B4 phase, which, with respect to width and helical pitch, occupies the place right between helical nano‐ and microfilaments. This morphology features a new internal structure not seen before for B4 phase morphologies.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Odd-even effects, oscillations in properties of materials comprised of an odd or even number of connected repeating units, are well-known phenomena in materials science. In organic materials, they ...are usually associated with the number of methylene groups in aliphatic chains. In this work, we unveil multiple signatures of a new odd-even effect in liquid crystals that occurs at the larger scale of molecular moieties that by themselves express liquid crystalline behavior. We demonstrate that oligomeric liquid crystals, with
n
= 1-4 number of rigid mesogenic segments connected by flexible aliphatic chains with an odd number of methylene groups, produce an odd-even effect in optical anisotropy and the bend elastic constant of the liquid crystal oligomer. This effect is different from the usual odd-even effects with respect to the parity of carbon atoms in an aliphatic chain and can be understood in term of the average molecular shape and the associations between
n
-mers based on the packing of these shapes. We also show that, in spite of the fact that there is no long-range electron density modulation, careful analysis of synchrotron SAXS results can provide important information about the molecular associations in the N and N
TB
phases that other techniques cannot access. This novel odd-even effect opens up a new mode to optimize phase and optical behavior.
We demonstrate a novel oligomeric odd-even effect of mesogenic segments connected by flexible chains with an odd number of methylene groups.
•Optical textures of lens shaped liquid crystal droplets have been studied in electric fields.•The formation of inversion walls normal to AC electric fields and their motion are observed.•The ...movement of the defect walls at low and high frequencies are theoretically explained.
Experimental studies of the structure of plano-convex lens shaped liquid crystal droplets subjected to electric fields are presented. Similar to previous observations by Salamon et al. (2020) in DC magnetic fields, we found the formation of an inversion wall normal to AC electric fields. While at low frequencies the direction of the wall is stationary, at higher frequencies it turns toward the external electric field. In both cases, the defect wall is also swept toward the periphery of the drop, where it eventually disappears. The linear displacement of the electric field-induced defect wall could be described by an exponential time dependence without any fitting parameter. This combined with threshold for director deformation enables to determine both the bend elastic constant and the rotational viscosity using much less substance than existing techniques. The rotation of the defect wall at high frequencies is a result of the antiparallel orientation of the effective moment vector and the electric field due to the lower dielectric constant and higher electric conductivity of the defect wall than of those of the rest of the liquid crystal droplet. Uniform electric field-induced generation, rotation and linear movement of defect walls is a unique phenomenon in soft matters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Freestanding slender fluid filaments of room‐temperature ferroelectric nematic liquid crystals are described. They are stabilized either by internal electric fields of bound charges formed due to ...polarization splay or by external voltage applied between suspending wires. The phenomenon is similar to those observed in dielectric fluids, such as deionized water, except that in ferroelectric nematic materials the voltages required are three orders of magnitudes smaller and the aspect ratio is much higher. The observed ferroelectric fluid threads are not only unique and novel but also offer measurements of basic physical quantities, such as the ferroelectric polarization and viscosity. Ferroelectric nematic fluid threads may have practical applications in nano‐fluidic micron‐size logic devices, switches, and relays.
Freestanding slender fluid filaments of a ferroelectric nematic liquid crystal are observed and studied. They are stabilized either by bound charges formed due to polarization splay or by external voltage applied between suspending wires. The slenderness ratio can exceed 100. Without external electric fields, the fluid ferroelectric filament becomes unstable in time due to ionic screening of the bound charges.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The interactions of phospholipids with liquid crystals have formed the basis for attractive biosensor technologies, but many questions remain concerning the basic physics and chemistry of these ...interactions. Phospholipids such as 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), at sufficiently high (∼1 μM) concentrations and/or sufficiently long times, turn the liquid crystal director perpendicular to the LC/water interface. If the other side of the LC film is in contact with a surface that prefers perpendicular alignment, the LC film appears completely dark between crossed polarizers. Recently, however, Popov et al. (J. Mater. Chem. B, 2017, 5, 5061) noted that at even higher (∼10 μM) DLPC concentrations, the liquid crystal texture brightens again between crossed polarizers. To explain this surprising observation, it was suggested that the LC interface might bend. In this paper we show by optical surface profiler measurements that indeed the interface of the LC film of 4-cyano-4'-octylbiphenyl (8CB) suspended in a transmission electron microscopy (TEM) grid with openings of ∼0.5 mm in diameter bends towards the lipid-coated interface. We demonstrate that where the bending occurs, the bent interface exhibits extreme sensitivity to air pressure variations, producing an optical response with acoustic stimulation. Finally, we suggest a physical mechanism for this astonishing result.
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