This paper is the first report of electrospinning neat polyisobutylene-based thermoplastic elastomers. Two generations of these materials are investigated: a linear ...poly(styrene-b-isobutylene-b-styrene) (L_SIBS) triblock copolymer and a dendritic poly(isobutylene-b-p-methylstyrene) (D_IB-MS), also a candidate for biomedical applications. Cross-polarized optical microscopy shows birefringence, indicating orientation in the electrospun fibers, which undergo large elongation and shear during electrospinning. In contrast to the circular cross section of L_SIBS fibers, D_IB-MS yields dumbbell-shaped fiber cross sections for the combination of processing conditions, molecular weight, and architecture. Hydrophobic surfaces with a water contact angle as high as 146 ± 3° were obtained with D_IB-MS that had the noncircular fiber cross section and a hierarchical arrangement of nano- to micrometer-sized fibers in the mat. These highly water repellent fiber mats were found to serve as an excellent scaffold for bovine chondrocytes to produce cartilage tissue.
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Electrospun liquid crystal fibres are promising media for gas sensing. However, accurately quantifying their response has been a challenge and until now limited to optical changes which utilise ...lasers and bulky detectors hindering the use for wear-able sensors. Herein, we make use of the resistive changes of the liquid crystal core polymer fibre mats (LCC-PFM) when exposed to volatile organic compounds (VOC). We found that these LCC-PFMs show reversible sensing of acetone at room temperature with response (recovery) times of ~14 (21) seconds and sensitivity as low as 10 ppm. This is comparable to the currently used metal-oxide-based sensors which typically operate at temperatures above 200 °C. These fibre mats are flexible, lightweight and in principle, can be easily miniaturised for use as resistive sensors to as small as 10 μm linear dimensions.
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Mechanically responsive organic materials can change their viscoelastic properties in response to external stimuli. However, materials that exhibit highly contrasting viscoelastic properties coupled ...with fast and reversible switching between the states involved have remained elusive. Here, it is shown that a nonsymmetric photoresponsive liquid crystal dimer exhibits photoswitching of its viscoelastic properties (shear viscosity, storage, and loss moduli) with remarkable contrast of up to 106 while transitioning between crystal and nematic phases. This switching is reversible and takes less than 100 s for both forward (trans‐cis photoisomerization) and backward (cis‐trans photoisomerization) reactions due to the coexistence of two allotropes containing two types of stereoisomers. This combination of highly contrasting viscoelastic behavior with fast and reversible switching establishes a whole new performance level for mechanically responsive organic materials and offers very considerable application potential in such diverse areas as photoswitchable adhesives, in vibration control, and as novel brakes.
Fast mechanical switch: Fast and giant photorheological effects are found in a liquid crystal dimer via crystal–liquid/liquid–crystal photomelting and crystallization processes.
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The present article entails a novel phenomenon of mechanoelectrical transduction, viz., electricity generation driven by ionic polarization/depolarization in various ion-containing solid polymer ...electrolyte membranes (PEMs) undergoing cantilever flexure. These PEMs were photopolymerized via UV irradiation in the miscible state of binary mixtures of poly(ethylene glycol) diacrylate (PEGDA) polymer precursors and ionic salts containing cations of different sizes and valencies (i.e., Li+, K+, Mg2+, and Al3+), where the counter bis(trifluoromethanesulfonyl)imide (TFSI–) anion was kept invariant. The influence of the cation types on the ionically driven mechanoelectrical responses, viz., flexoelectricity, was investigated in relation to the ionic conductivity and mechanical and thermal characteristics of the PEMs, undergoing intermittent square-mode bending. Of particular interest is the observation of a systematic electrical response upon manipulation of the ionic valency/size ratio of the dissociated cations, i.e., a higher response was found in the case of a larger valency/size ratio. Additionally, mechanoelectrical energy conversion was estimated to increase with increasing cation valency/size ratio (viz., Al3+). Understanding the mechanoelectrical transduction behavior of the present ion-containing PEMs, referred to as flexoionic PEMs, will enable their utilization in sensing and clean energy-harvesting applications from the natural environment such as wind and oceanic wave motions.
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•Simultaneously applied electric and magnetic fields make inversion walls unstable in nematic droplets.•A zig-zag instability of straight inversion walls occurs above a threshold ...voltage.•The time and field dependences of the shape and motion of the buckled walls show soliton-like behavior.•A proposed physical mechanism involves the droplet shape and elastic anisotropy.
Lens-shaped liquid crystal samples have the potential for their use in tunable multifocal optical lenses. In previous observations (Phys. Rev. Research, 2, 023261 (2020) and J. Mol. Liq., 334, 116085 (2021)) plano-convex spherical lens-shaped liquid crystal sessile droplets were studied either in magnetic or AC electric fields, and the formation of an inversion wall (a one-dimensional soliton) moving toward the periphery was observed and explained.
Here we present experimental observations of the structure of plano-convex lens-shaped nematic liquid crystal droplets subjected to simultaneous competing magnetic and electric fields. It is found that above a threshold electric field the initially straight defect wall buckles to form a zig-zag shape. This phenomenon is compared to those observed in sandwich cells with uniform thickness and the differences in their theoretical description are discussed.
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We present small-angle X-ray scattering, polarized optical microscopy and electric current measurements of a sulfur-containing bent-core liquid crystal material for characterization of the layer and ...director structures, thermally and electrically driven transitions between antiferroelectric and ferroelectric structures and switching properties. It was found that the material has polarization-modulated homochiral synclinic ferroelectric (SmCsPFmod), homochiral anticlinic antiferroelectric (SmCaPA) and racemic synclininc antiferroelectric (SmCsPA) structures that can be reversibly switched between each other either thermally and/or electrically. High switching polarization combined with softness of the liquid crystalline structure makes this compound a good candidate for applications in high-power capacitors and electrocaloric devices.
A highly sensitive label‐free liquid crystal (LC)‐based technique is presented for detecting Immunoglobulin G (IgG) antigens used to uncover viral infections. The effectiveness, sensitivity, and ...selectivity of this detection method is demonstrated with goat IgG antigen at concentrations as low as 100 pg ml−1, which is comparable to the sensitivity of the current enzyme‐linked immunosorbent assay (ELISA). The sensor is fabricated by decorating a transmission electron microscopy grid immobilized glass surfaces with antibodies; the target antigen is detected by a liquid crystal suspended onto the grid. This is different from previous methods where the antigen is detected either at the LC‐aqueous interface or in an LC sandwich cell with an antibody/antigen‐decorated substrate. This new approach has advantages such as easy sample preparation, higher sensitivity, and better storage capabilities. Binding the target antigen to the antibody results in a reorientation of the LC director that is detected optically. In addition to demonstrating the sensitivity, the physical principle of the detection is also discussed. This technique may apply to detect virtually any antigen of interest.
A novel, highly sensitive label‐free liquid crystal‐based sensor is developed to detect Immunoglobulin G antigens. A substrate holding a transmission electron microscope (TEM) grid is decorated with antibodies. Upon incubation with a specific antigen, the antigen‐antibody complex can be identified by filling the TEM grid with a nematic liquid crystal that shows a uniform color under crossed polarizers.
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In this paper, we discuss the preparation and several electrical properties of two ionic Liquid Crystal Elastomers. We show that iLCEs can be used as electric actuators, bending sensors and as solid ...electrolytes of organic electrochemical transistors. We summarise the results using one type of LCE and two types of ionic liquids. It is found that the ionic liquid that phase separates from the reactive mesogenic monomers and forms micron size ionic channels performs better than the less phase separating ionic liquid. The switching time of the order of a second was found to be possible using the ionic liquid with smaller ions and larger channels. These results provide many exciting opportunities in various areas and impact future applications, although they are far from optimised. Fine tuning of the high-performance iLCEs require an intricate compatibility between the LCE and the electrodes and appears to be laborious. On the other hand, the first promising results justify the efforts to study more type of liquid crystal elastomers, ionic liquids and compliant electrodes.
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We have developed a prototype of breathable thermochromic textile ideal for sensor applications, e.g., medical thermography. The textile was woven/knitted from polyester filaments pre-coated with ...thermochromic liquid crystal (TLC) ink, in lieu of coating the TLC ink on the woven/knitted textile. This process brings us closer to achieving breathable thermochromic textiles while enhancing the versatility of the textile. A combination of precoated yarns can be preselected according to the desired thermochromic properties of the textile. Swatches from both knitted and handwoven fabrics showed excellent reversible thermochromic property showing color from red to blue as the temperature is raised from 26 to 32 °C, consistent with the unincorporated TLC ink.
A series of 1-biphenyl-4-alkyl-1,2,3-triazole-based liquid crystal compounds were synthesised via a fast and efficient microwave mediated 'Click Reaction' and their phase behaviour is presented. Most ...of the 1-(3-fluorobiphenyl)-4-alkyl-1,2,3-triazole compounds exhibited a smectic A phase with relatively low transition temperatures compared to previously examined aryl-triazole-based mesogens. Small angle X-ray scattering measurement indicated the existence of deep smectic phase for some cases. Structural variations gave rise to different phase behaviour in these triazole-based compounds.
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