Highly Oriented Nanofibrils of Regioregular Poly(3‐hexylthiophene) Formed via Block Copolymer Self‐Assembly in Liquid Crystals

A novel method making use of block copolymer self‐assembly in nematic liquid crystals (LCs) is described for preparing macroscopically oriented nanofibrils of π‐conjugated semiconducting polymers. Upon cooling, a diblock copolymer composed of regioregular poly(3‐hexylthiophene) (P3HT) and a liquid crystalline polymer (LCP) in a block‐selective LC solvent can self‐assemble into oriented nanofibrils exhibiting highly anisotropic absorption and polarized photoluminescence emission. An unusual feature of the nanofibrils is that P3HT chains are oriented along the fibrils' long axis. This general method makes it possible to use LCs as an anisotropic medium to grow oriented nanofibrils of many semiconducting polymers insoluble in LCs.     

Nematic Anisotropic Liquid‐Crystal Gels—Self‐Assembled Nanocomposites with High Electromechanical Response

The uniqueness of liquid crystals (LCs) lies in the large anisotropies of their properties, which can be utilized to generate high electromechanical responses. In a properly oriented LC polymer system, an external electric field can induce reorientation of the mesogenic units possessing a dielectric anisotropy, which, when coupled with the shape anisotropy of the mesogenic units, can in turn produce large mechanical strain. Anisotropic LC gels, which can be obtained by in‐situ photopolymerization of the reactive LC molecules in the presence of non‐reactive LC molecules in an oriented state, are an example of such liquid‐crystal polymer systems. It is shown here that a homeotropically aligned LC gel in its nematic phase exhibits high electrically induced strain (> 2 %) with an elastic modulus of 100 MPa and a high electromechanical conversion efficiency (75 %) under an electric field of 25 MV/m. These anisotropic LC polymeric materials could provide a technologically compatible system for such applications as artificial muscles and as microelectromechanical devices.     

Liquid‐Crystalline Electrolytes for Lithium‐Ion Batteries: Ordered Assemblies of a Mesogen‐Containing Carbonate and a Lithium Salt

Thermotropic liquid‐crystalline (LC) electrolytes for lithium‐ion batteries are developed for the first time. A rod‐like LC molecule having a cyclic carbonate moiety is used to form self‐assembled two‐dimensional ion‐conductive pathways with lithium salts. Electrochemical and thermal stability, and efficient ionic conduction is achieved for the liquid crystal. The mixture of the carbonate derivative and lithium bis(trifluoromethylsulfonyl)imide is successfully applied as an electrolyte in lithium‐ion batteries. Reversible charge–discharge for both positive and negative electrodes is observed for the lithium‐ion batteries composed of the LC electrolyte.     

Enhanced Hole‐Transporting Behavior of Discotic Liquid‐Crystalline Physical Gels

Discotic liquid‐crystalline (LC) physical gels have been prepared by combining the self‐assembled fibers of a low‐molecular‐weight gelator and semiconducting LC triphenylene derivatives. The hole mobilities of the discotic LC physical gels measured by a time‐of‐flight method become higher than those of LC triphenylenes alone. The introduction of the finely dispersed networks of the gelator in the hexagonal columnar phases may affect the molecular dynamics of the liquid crystals, resulting in the enhancement of hole transporting behavior in the LC gel state.     

Light‐Driven Liquid Crystalline Networks and Soft Actuators with Degree‐of‐Freedom‐Controlled Molecular Motors

Design and fabrication of photomechanical soft actuators has attracted intense scientific interest because of their potential in the manufacture of untethered intelligent soft robots and advanced functional devices. Trifunctional and monofunctional polymerizable molecular motors are judiciously designed and synthesized. Novel light‐driven liquid crystalline networks (LCN) are prepared by crosslinking overcrowded‐alkene‐based molecular motors with different degrees of freedom into the anisotropic LCN. The photoisomerization and thermal helix inversion of light‐driven molecular motors are reversible when only the upper part of the molecular motor is linked to the network, endowing the LCN film with remarkable photoactive performance. However, photochemical geometric change of the light‐driven molecular motor does not work after crosslinking both the upper and lower part of the motor by polymer chains. Interestingly, it is found that the fastened motor can transfer the light energy into localized heat instead of performing photoisomerization. The light‐driven molecular‐motor‐based LCN soft actuators are demonstrated to function as a grasping hand, where the continuous motions of grasping, moving, lifting, and releasing an object are successfully achieved. This work may provide inspiration to the preparation of next‐generation photoactive advanced functional materials toward their wide applications in the areas of photonics, optoelectronics, soft robotics, and beyond.     

Electric‐Field‐Controlled Alignment of Rod‐Shaped Fluorescent Nanocrystals in Smectic Liquid Crystal Defect Arrays

Periodic micro‐arrays of straight linear defects containing nanoparticles can be created over large surface areas at the transition from the nematic to smectic‐A phase in a nanoparticle–liquid crystal (LC) composite material confined under the effect of conflicting anchoring conditions (unidirectional planar vs normal) and electric fields. Anisomeric dichroic dye molecules and rod‐shaped fluorescent semiconductor nanocrystals (dot‐in‐rods) with large permanent electric dipole and high linearly polarized photoluminescence quantum yield align parallel to the local LC molecular director and follow its reorientation under application of the electric field. In the nano‐sized core regions of linear defects, where the director is undefined, anisotropic particles align parallel to the defect whereas spherical quantum dots do not show any particular interaction with the defect. Under application of an electric field, ferroelectric semiconductor nanoparticles in the core region align along the field, perpendicular to the defect direction, whereas dichroic dyes remain parallel to the defect. This study provides useful insights into the complex interaction of anisotropic nanoparticles and anisotropic soft materials such as LCs in the presence of external fields, which may help the development of field‐responsive nanoparticle‐based functional materials.     

Fast and High‐Contrast Electro‐optical Switching of Liquid‐Crystalline Physical Gels: Formation of Oriented Microphase‐Separated Structures

Fast and high‐contrast responses with low driving voltages in twisted nematic (TN) cells are achieved for anisotropically oriented structures of liquid‐crystalline physical gels. They are prepared by hydrogen‐bonded aggregation of an L ‐lysine‐based gelator in nematic liquid crystals. When the mixtures of the nematic liquid crystals and the gelator are prepared in TN cells, fibrous aggregates of the gelator align along the twisted‐nematic orientation of the liquid crystal, forming oriented phase‐separated structures.     

Electrotunable Non‐reciprocal Laser Emission from a Liquid‐Crystal Photonic Device

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.     

Alignment of a Perylene‐Based Ionic Self‐Assembly Complex in Thermotropic and Lyotropic Liquid‐Crystalline Phases

The thermotropic and lyotropic liquid‐crystalline (LC) phases of the ionic self‐assembled complex N,N′,‐bis(2‐(trimethylammonium)ethylene)‐perylene‐3,4,9,10‐tetracarboxyldiimide‐bis(2‐ethylhexyl)sulfosuccinate have been studied using polarizing microscopy, differential scanning calorimetry (DSC), and X‐ray scattering techniques. A two‐dimensional (2D) columnar thermotropic LC phase with π–π stacking of the perylene tectonic units and a lyotropic LC phase in dimethyl sulfoxide (DMSO) have been found. Different techniques have been applied to align both systems and included: surface interactions, electric and magnetic fields, shear force, and controlled domain formation at the LC–isotropic phase‐transition front (PTF). Characterization of the alignment in films has been performed using polarized UV‐vis spectroscopy and transmission null‐ellipsometry. The best results have been obtained for alignment of the material in a lyotropic phase by controlled domain formation at the PTF of the LC–isotropic phase transition. In this case, a dichroic ratio of 18 is achieved with packing of columns of perylenediimide tectons perpendicular to the PTF.     

Size‐Scalable and High‐Density Liquid‐Metal‐Based Soft Electronic Passive Components and Circuits Using Soft Lithography

The use of conducting liquids with high electrical conductivity, such as eutectic gallium–indium (EGaIn), has great potential in electronics applications requiring stretchability and deformability beyond conventional flexible electronics relying on solid conductors. An advanced liquid metal thin‐line patterning process based on soft lithography and a compatible vertical integration technique are presented that enable size‐scalable and high‐density EGaIn‐based, soft microelectronic components and circuits. The advanced liquid metal thin‐line patterning process based on poly(dimethylsiloxane) (PDMS) substrates and soft lithography techniques allows for simultaneous patterning of uniform and residue‐free EGaIn lines with line width from single micrometers to several millimeters at room temperature and under ambient pressure. Using this fabrication technique, passive electronic components and circuits are investigated under elastic deformations using numerical and experimental approaches. In addition, soft through‐PDMS vias with high aspect ratio are demonstrated for multilayer interconnections in 2.5D and 3D integration approaches. To highlight the system‐level potential of the patterning technique, a chemical sensor based on an integrated LC resonance circuit with a microfluidic‐tunable interdigitated capacitor and a planar spiral inductor is fabricated and characterized. Finally, to show the flexibility and stretchability of the resulting electronics, circuits with embedded light emitting diodes (LEDs) are investigated under bending, twisting, and stretching deformations.     

Photoresponsive Ferroelectric Liquid‐Crystalline Polymers

The photoresponse of ferroelectric smectic side‐chain liquid‐crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans–cis isomerization on the material's phase‐transition temperatures and its ferroelectric properties (spontaneous electric polarization P_S and director tilt angle θ) are analyzed. It turns out that the Curie temperature (transition S_C* to S_A) can be reversibly shifted by up to 17 °C. The molecular mechanism of this “photoferroelectric effect” is studied in detail using time‐resolved measurements of the dye's optical absorbance, the director tilt angle, and the spontaneous polarization, which show a direct response of the ferroelectric parameters to the molecular isomerization. The kinetics of the thermal reisomerization of the azo dye in the LC matrix are evaluated. A comparison to the reisomerization reaction in isotropic solution (toluene) reveals a faster thermal relaxation of the dye in the LC phase.     

Scalable One‐Step Wet‐Spinning of Graphene Fibers and Yarns from Liquid Crystalline Dispersions of Graphene Oxide: Towards Multifunctional Textiles

Key points in the formation of liquid crystalline (LC) dispersions of graphene oxide (GO) and their processability via wet‐spinning to produce long lengths of micrometer‐dimensional fibers and yarns are addressed. Based on rheological and polarized optical microscopy investigations, a rational relation between GO sheet size and polydispersity, concentration, liquid crystallinity, and spinnability is proposed, leading to an understanding of lyotropic LC behavior and fiber spinnability. The knowledge gained from the straightforward formulation of LC GO “inks” in a range of processable concentrations enables the spinning of continuous conducting, strong, and robust fibers at concentrations as low as 0.075 wt%, eliminating the need for relatively concentrated spinning dope dispersions. The dilute LC GO dispersion is proven to be suitable for fiber spinning using a number of coagulation strategies, including non‐solvent precipitation, dispersion destabilization, ionic cross‐linking, and polyelectrolyte complexation. One‐step continuous spinning of graphene fibers and yarns is introduced for the first time by in situ spinning of LC GO in basic coagulation baths (i.e., NaOH or KOH), eliminating the need for post‐treatment processes. The thermal conductivity of these graphene fibers is found to be much higher than polycrystalline graphite and other types of 3D carbon based materials.     

Mesomorphic Organization and Thermochromic Luminescence of Dicyanodistyrylbenzene‐Based Phasmidic Molecular Disks: Uniaxially Aligned Hexagonal Columnar Liquid Crystals at Room Temperature with Enhanced Fluorescence Emission and Semiconductivity

A new dicyanodistyrylbenzene‐based phasmidic molecule, (2Z,2′Z)‐2,2′‐(1,4‐phenylene)bis(3‐(3,4,5‐tris(dodecyloxy)phenyl)acrylonitrile), GDCS, is reported, which forms a hexagonal columnar liquid crystal (LC) phase at room temperature (RT). GDCS molecules self‐assemble into supramolecular disks consisting of a pair of molecules in a side‐by‐side disposition assisted by secondary bonding interactions of the lateral polar cyano group, which, in turn, constitute the hexagonal columnar LC structure. GDCS shows very intense green/yellow fluorescence in liquid/solid crystalline states, respectively, in contrast to the total absence of fluorescence emission in the isotropic melt state according to the characteristic aggregation‐induced enhanced emission (AIEE) behavior. The AIEE and two‐color luminescence thermochromism of GDCS are attributed to the peculiar intra‐ and intermolecular interactions of dipolar cyanostilbene units. It was found that the intramolecular planarization and restricted molecular motion associated with a specific stacking situation in the liquid/solid crystalline phases are responsible for the AIEE phenomenon. The origin of the two‐color luminescence was elucidated to be due to the interdisk stacking alteration in a given column driven by the specific local dipole coupling between molecular disks. These stacking changes, in turn, resulted in the different degree of excited‐state dimeric coupling to give different emission colors. To understand the complicated photophysical properties of GDCS, temperature‐dependent steady‐state and time‐resolved PL measurements have been comprehensively carried out. Uniaxially aligned and highly fluorescent LC and crystalline microwires of GDCS are fabricated by using the micromolding in capillaries (MIMIC) method. Significantly enhanced electrical conductivity (0.8 × 10^?5 S?cm^?1/3.9 × 10^?5 S?cm^?1) of the aligned LC/crystal microwires were obtained over that of multi‐domain LC sample, because of the almost perfect shear alignment of the LC material achieved in the MIMIC mold.     

ZnSe–Si Bi‐coaxial Nanowire Heterostructures

We report on the fabrication, structural characterization, and luminescence properties of ZnSe/Si bi‐coaxial nanowire heterostructures. Uniform ZnSe/Si bi‐coaxial nanowire heterostructures are grown on silicon substrates by the simple one‐step thermal evaporation of ZnSe powder in the presence of hydrogen. Both ZnSe and silicon are single‐crystalline in the bi‐coaxial nanowire heterostructures, and there is a sharp interface along the nanowire axial direction. Furthermore, secondary nanostructures of either ZnSe nanobrushes or a SiO_x sheath are also grown on the primary bi‐coaxial nanowires, depending on the ratio of the source materials. The experimental evidence strongly suggests that bi‐coaxial nanowires are formed via a co‐growth mechanism, that is, ZnSe terminates specific surfaces of silicon and leads to anisotropic, one‐dimensional silicon growth, which simultaneously serves as preferential nucleation sites for ZnSe, resulting in the bi‐coaxial nanowire heterostructures. In addition, the optical properties of ZnSe/Si nanowires are investigated using low‐temperature photoluminescence spectroscopy.     

Hydrotalcites Catalyze the Acidolysis Polymerization of Phenolic Acid to Create Highly Heat‐Resistant Bioplastics

Acidolysis polymerization has been used to prepare phenol‐derived polymers such as liquid crystalline (LC) polymers, and is catalyzed by mildly‐alkaline salts. The catalytic effects of hydrotalcites (HTs), which are natural alkalescent minerals with controllable basicity, are investigated on the acidolysis copolymerization of coumarates such as p‐coumaric acid and caffeic acid. As a result, the LC copolymer prepared in the presence of HT with a Mg/Al ratio of 3 shows higher molecular weight values than copolymers prepared in the presence of any other alkalescent salts. On the other hand, the copolymers prepared in the presence of HTs show a clear LC state where the polymer chains are oriented on the surface of the glass fibers. The resin, which is oriented by glass fiber fillers aligning along its longitudinal axis and is annealed at 300 °C for 20 min, shows a softening temperature of 305 °C while keeping a high mechanical strength of 85 MPa and a high mechanical modulus over 1 GPa.     

A Stimuli‐Responsive,Photoluminescent, Anthracene‐Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical Processes

Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable–stable phase transition induced by external stimuli is prepared. A 2,6‐diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6‐diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid‐crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic‐columnar phase transition induced by heating or mechanical shearing for this 2,6‐diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable–stable LC phase transition.     

Thermo‐Mechanical Responses of Liquid‐Crystal Networks with a Splayed Molecular Organization

Films of liquid‐crystal networks with a splayed molecular alignment over their cross‐section display a well‐controlled deformation as a function of temperature. The deformation can be explained in terms of differences in thermal expansion depending on the average molecular orientation of the mesogenic centers of the monomeric units. The thermal expansion of the anisotropic polymers has been characterized as a function of their molecular structure and the polymerization conditions. As a reference, films with an in‐plane 90° twist have also been studied and compared with the splayed, out‐of‐plane molecular rotation. The twisted films show a complex macroscopic deformation owing to the formation of saddle‐like geometries, whereas the deformation of the splayed structured is smooth and well controlled. The deformation behavior is anticipated to be of relevance for polymer‐based microelectromechanical system (MEMS) technology.     

Molecularly‐Engineered, 4D‐Printed Liquid Crystal Elastomer Actuators

Three‐dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual thiol‐ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo‐responsive structures that sequentially and reversibly undergo multiple shape changes.     

Anthracene‐Containing Binaphthol Chromophores for Light‐Emitting Diode (LED) Fabrication

Non‐crystalline anthracene‐containing binaphthol chromophores were synthesized, characterized, and used in the fabrication of organic light‐emitting diodes (OLEDs). Specifically, the target molecules were 2,2′‐dihexyloxy‐1,1′‐binaphthol‐6,6′‐bisanthracene ( BA1 ) and 2,2′‐dimethoxyy‐1,1′‐binaphthol‐6,6′‐bisanthracene ( BA2 ). Molecules BA1 and BA2 provide amorphous solids, as determined by their glass‐transition temperature (T_g) measured by differential scanning calorimetry (DSC). Efficient multilayer OLEDs containing BA1 and BA2 were fabricated by evaporation techniques. Differences in the electroluminescence frequencies of these devices suggests that the degree of alkoxide substitution controls the mobility within the binaphthol material, and therefore the recombination region in the device. Compound BA2 can also be used to dope CBP ((4,4′‐bis(carbazol‐9‐yl)biphenyl)) in the fabrication of highly efficient OLEDs.     

Conducting Polymer Based Visual‐Aided Smart Thermosensors on Arbitrary Substrates

Conducting polymers have shown appealing performances as sensing materials in various smart sensors such as gas, chemical and biological sensors, owing to their unique physical and electrical properties. This study reports a novel development for the fabrication of visual‐aided smart thermal (VAST) sensors. The sensors are based on conducting polymers, temperature‐sensitive resin, and liquid crystal molecules via direct scrawling and in situ solventless polymerization. In the VAST sensor, the thermochromism resins and liquid crystals form a visual‐aided system with the real‐time early warning function and the conducting polymers provide an ultrahigh resolution by the measure of the change of resistivity. Additionally, these VAST sensors also hold the advantages of low cost, using simple tools, high stability, excellent adaptability to arbitrary substrates, wide application fields, and facile large‐scale fabrication. These properties are in favor of fabricating smart thermal sensors to satisfy the practical demands, such as the demonstrated temperature detecting system (especially flexible devices with nonplanar surface), thermodefect diagnostic system, smart battery monitoring system, and other environment monitoring.