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For over decades, nematic liquid crystals have been recognized as highly fluidic materials that respond to electric field on the millisecond scale. In contrast to traditional nematics with fast responsivity, we herein report nontrivial ultraslow electric-driven dynamics in bent-shaped nematic materials. Varying the alkyl chain spacers of bent-shaped cyanobiphenyl dimers (COO

Stabilization and diversification of phase behaviors in ferroelectric nematics driven by a stereoisomer effect are observed, which in turn modulates the viscoelastic and ferroelectric properties.

The emerging ferroelectric nematic liquid crystals have been attracting broader interests in new liquid crystal physics and their unique material properties. One big challenge for the ferroelectric nematic research is to enrich the material choice, which is now limited to

Circular dichroism is a technologically important phenomenon contrasting the absorption and resultant emission properties between left- and right-handed circularly polarized light. While the chiral handedness of systems mainly determines the mechanism of the circular dichroism in linear optics, the counterpart in the nonlinear optical regime is nontrivial. Here, in contrast to traditional nonlinear circular dichroism responses from structured surfaces, we report on an unprecedented bulk-material-induced circular dichroism of second harmonic generation with a massive g-factor up to 1.8.

Sessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarization optical (video)microscopy (POM). During heating/cooling cycles, at first, the droplets change their shape from spherical to extended ellipsoidal. Then they start to move rapidly along the surface electric field, i.e., along the crystal's polar axis (c-axis). During this motion, several droplets merge into running streams (tendrils) extending towards the edges of the top surface area. Finally, practically all liquid crystalline material is transported from the top surface to the side surfaces of the crystal. At stabilized temperature, laser illumination of the assembly causes dynamic processes that are localized to the illuminated area. Also, in this case, the LC droplets merge into several tendril-like formations that are preferentially oriented along the c-axis of the crystal. The pattern of tendrils fluctuates with time, but it persists as long as the illumination is present. In this case, the LC material is transported between the central and the edge region of the illuminated area., 16 pages, 5 figures. arXiv admin note: text overlap with arXiv:2208.02318

Second-order optical nonlinearity is the essential concept for realizing modern technologies of optical wavelength conversion. The emerging helical polarization fluid, dubbed helielectric nematic, now makes it possible to design and easily fabricate various polarization structures and control their optical responses. The matter family is demonstrated as an ideal liquid platform for nonlinear optical conversion and amplification with electric-reconfigurable tunability. We here develop a universal phase matching theory and reveal a nonclassic chirality-sensitive phase-matching condition in the polarization helices through both the numerical calculation and the experimental validations. The nonlinear optical amplification can be dramatically modulated with a contrast ratio of >100:1 by an in-plane electric field. Furthermore, we employ the director relaxation under electric fields coupled with nonlinear optical simulation to clarify the topology–light interactions.

The understanding of correlations between molecular details and macroscopic material behavior is a fundamental question of molecular chemistry/physics and offers practical interest in materials design with fine-property-tunability. Herein, we demonstrate extreme modulation of liquid crystal (LC) viscoelasticity triggered by a reversion of the ester bond direction in two series of sulfur-containing cyanobiphenyl-based LC dimers. They possess two oppositely directed ester linkages (i.e., COO or OCO), namely COOn and OCOn, respectively, and different carbon atom numbers of the short alkylene spacers (n = 4 and 6). Unexpectedly, it has been proven that the COOn homologs exhibit extraordinarily enhanced viscoelastic properties in the fluidic nematic (N) phase (up to about 1000 times) compared with their OCOn counterparts. Besides, dielectric spectroscopy revealed that the degree of the collective orientational fluctuation is significantly affected by reversing the ester bond direction, suggesting the existence of heliconical clusters embedded in the N state. Finally, we have proposed a novel eco-driving LC memory device based on a pulse-electric-field driving method using COO4 with an extremely high rotational viscosity.

The generation of spatially localized, soliton-like hydrodynamic disturbances in microscale fluidic systems is an intriguing challenge. Herein, we introduce nonequilibrium solitons in nematic liquid crystals stimulated by an electric field. These dynamic solitons are robust as long as the electric field is maintained. Interestingly, their kinetic behaviours depend on the field condition—Tuning of the amplitude and frequency of the applied electric field alters the solitons to self-assemble into lattice ordering like physical particles or to command them to various dynamic states. Our key property to the realisation is the electrohydrodynamic instability due to the coupling between the fluid elasticity and the background convection. This paper describes a new mechanism for realising dynamic solitons in fluid systems on the basis of the electrohydrodynamic phenomena., Electric field induced convective instabilities in liquid crystal slabs can assume a localized shape. The authors show how to generate, manipulate and shepard these dissipative solitary excitations that do not require topological constraints for stabilization.

The twist–bend nematic (NTB) phase is one of the new types of nematics found recently, which possesses local nematic order with a heliconical orientational modulation at the nanoscale. Herein, we quantitatively determined, for the first time, the temperature-dependent elastic and viscosity properties in both the nematic (N) and NTB phases using a thioether-linked cyanobiphenyl dimer CBS7SCB exhibiting a broad temperature range of the NTB phase which is stable down to room temperature. In the N phase, the fundamental elastic moduli: splay and bend elastic moduli (K11 and K33, respectively) are found to be in the order of 10−12 N, and the effective rotational viscosity (γ1) is determined to be in the range of 5–200 mPa s. Meanwhile, the NTB phase is found to exhibit a compressive elastic modulus B in the order of several tens of kilopascals, the effective K11 in the order of 10−10–10−8 N, and a considerably large γ1 value of ∼68.7 Pa s right below the N–NTB phase transition. The present study provides insights into the comprehensive viscoelastic properties based on comparison of the obtained experimental data with not only the existing theoretical prediction but also the preceding experimental works.

Just like in living organisms, if precise coherent operation of tiny movable components is possible, one may generate a macroscopic mechanical motion. Here we report that ~1010 pieces of colloidally dispersed nanosheets in aqueous media can be made to operate coherently to generate a propagating macroscopic wave under a non-equilibrium state. The nanosheets are initially forced to adopt a monodomain cofacial geometry with a large and uniform plane-to-plane distance of ~420 nm, where they are strongly correlated by competitive electrostatic repulsion and van der Waals attraction. When the electrostatic repulsion is progressively attenuated by the addition of ionic species, the nanosheets sequentially undergo coherent motions, generating a propagating wave. This elaborate wave in time and space can transport microparticles over a long distance in uniform direction and velocity. The present discovery may provide a general principle for the design of macroscopically movable devices from huge numbers of tiny components., Tiny movable components could generate macroscopic mechanical motion if precise coherent operation can be exerted simultaneously. Here, the authors demonstrate this by using 10^10 pieces of colloidally dispersed nanosheets to generate wave under non-equilibrium state.

The emerging ferroelectric nematic (NF) liquid crystal is a novel 3D-ordered liquid exhibiting macroscopic electric polarization. The combination of the ultrahigh dielectric constant, strong nonlinear optical signal, and high sensitivity to the electric field makes NF materials promising for the development of advanced liquid crystal electroopic devices. Previously, all studies focused on the rod-shaped small molecules with limited length (l) range and dipole moment (μ) values. Here, through the precision synthesis, we extend the aromatic rod-shaped mesogen to oligomer/polymer (repeat unit up to 12 with monodisperse molecular-weight dispersion) and increase the μ value over 30 Debye (D). The NF phase has a widespread existence far beyond our expectation and could be observed in all the oligomer/polymer length range. Notably, the NF phase experiences a nontrivial evolution pathway with the traditional apolar nematic phase completely suppressed, i.e., the NF phase nucleates directly from the isotropic liquid phase. The discovery of thte ferroelectric packing of oligomer/polymer rods not only offers the concept of extending the NF state to oligomers/polymers but also provides some previously overlooked insights in oxybenzoate-based liquid crystal polymer materials.

Significance The recent discovery of the emerging ferroelectric nematics opens an avenue not only for exploring exotic polar matter states in condensed matter physics but also for providing opportunities toward brand new liquid crystal technologies. Here, we revealed the existence of a helielectric nematic state by introducing the chirality into the ferroelectric nematics. Combining multiple intercorrelated measurements, we confirmed a helicoidal-type polar vector field in the helielectric nematics. The emergent polar symmetry triggers distinctions in topology to the dielectric cholesterics. Via proper doping of chiral generators, the helielectric state can survive down to room temperature, retaining excellent nonlinear optical and dielectric properties. Hence, it offers a stable material platform for exploring unidentified polarity–chirality–coupled textures and developing functional electrooptical devices.

Geometric structures are commonly encountered in natural and designed systems. However, the bottom-up fabrication of regular geometric assemblies with precise dimensional control, especially from soft materials, poses an outstanding challenge in contemporary materials science and chemistry. Herein, we present a general method for the preparation of colloidally stable, hexagonal platelets via the formation of crystalline inclusion complexes of tris-o-phenylenedioxycyclotriphosphazene and block copolymers bearing interactive blocks. Dictated by the screw dislocation growth of inclusion complexes, uniform hexagonal platelets with precisely controllable dimensions can be prepared. This supramolecular assembly approach is further utilized to produce concentric hexagonal platelets via stepwise seeded growth from various inclusion complexes.

Pearl-shaped polar molecules with high enough dipole moment enable the creation of the giant-ε ferroelectric nematics., Superhigh-ε materials that exhibit exceptionally high dielectric permittivity are recognized as potential candidates for a wide range of next-generation photonic and electronic devices. In general, achieving a high-ε state requires low material symmetry, as most known high-ε materials are symmetry-broken crystals. There are few reports on fluidic high-ε dielectrics. Here, we demonstrate how small molecules with high polarity, enabled by rational molecular design and machine learning analyses, enable the development of superhigh-ε fluid materials (dielectric permittivity, ε > 104) with strong second harmonic generation and macroscopic spontaneous polar ordering. The polar structures are confirmed to be identical for all the synthesized materials. Furthermore, adapting this strategy to high–molecular weight systems allows us to generalize this approach to polar polymeric materials, creating polar soft matters with spontaneous symmetry breaking.

This study focused on the use of nonconventional bent-core π-electronic systems, 2,2'-bipyrroles substituted with modified benzoyl units, as building units of stimuli-responsive assemblies. Electric-field-responsive mesophase behaviors were observed in homochiral synclinic ferroelectric smectic C structures comprising the

Optical properties of aqueous colloidal dispersions of 2D electrolytes, if their aspect ratios are extra-large, can be determined by their orientation preferences. Recently, we reported that a colloidal dispersion of diamagnetic titanate(IV) nanosheets (TiIVNSs), when placed in a magnetic field, is highly anisotropic because TiIVNS anomalously orients its 2D plane orthogonal to the magnetic flux lines due to its large anisotropic magnetic susceptibility. Herein, we report a serendipitous finding that TiIVNSs can be in situ photochemically reduced into a paramagnetic species (TiIV/IIINSs), so that their preference of magnetic orientation changes from orthogonal to parallel. This transition distinctly alters the structural anisotropy and therefore optical appearance of the colloidal dispersion in a magnetic field. We also found that TiIV/IIINSs is autoxidized back to TiIVNSs under non-deaerated conditions. By using an elaborate setup, the dispersion of TiIVNSs serves as an optical switch remotely operable b...

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material's rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

The construction of hierarchical nanostructures with precise morphological and dimensional control has been one of the ultimate goals of contemporary materials science and chemistry, and the emulation of tailor-made nanoscale superstructures realized in the nature, using artificial building blocks, poses outstanding challenges. Herein we report a one-pot strategy to precisely synthesize hierarchical nanostructures through an in-situ initiation-growth process from a liquid crystalline block copolymer. The assembly process, analogous to living chain polymerization, can be triggered by small-molecule, macromolecule or even nanoobject initiators to produce various hierarchical superstructures with highly uniform morphologies and finely tunable dimensions. Because of the high degree of controllability and predictability, this assembly strategy opens the avenue to the design and construction of hierarchical structures with broad utility and accessibility., Construction of hierarchical nanostructures is important in material science, but precise morphological control remains a challenge. Here, the authors report a one-pot in-situ initiation-growth process from a liquid crystalline block copolymer to precisely control the morphology and dimensions of hierarchical nanostructures.

We investigate the structure and the magnetooptical response of isotropic and anisotropic fibrillous organoferrogels with mobile magnetic nanoparticles (MNPs). We demonstrate that the presence of the gel network restricts the magnetooptical response of the ferrogel. Even though the ferrogel exhibits no magnetic hysteresis, an optical hysteresis has been found. This suggests that the magnetooptical response is primarily determined by the dynamics of self-assembly of the MNPs into shape-anisotropic agglomerates. Furthermore, we show that the optical anisotropy of the system can be fine-tuned by varying the concentration of the gelator and the MNPs, respectively. The optical response in structurally anisotropic gels becomes orientation-dependent, revealing an intricate interplay between the gel mesh and the MNPs.

Azodendrimer is a class of branched polymer, whose structure can be modulated by light irradiation. Recently, a new type of liquid crystalline dendrimers that serve as a command surface has been reported. They received tremendous attention due to the fundamental interests of the variation of their properties (e.g., alignment, topology) in response to light. Here, we explore the properties of the surface anchoring, molecular conformation and the phase structure of a model azodendrimer. We proposed a proper molecular conformation of the azodendrimer based on density functional theory analysis and molecular dynamics. Also, we reveal (1) the minimum coverage ratio of the dendrimer for inducing homeotropic alignment of host liquid crystals and the polar anchoring strength; (2) unlike typical low-molecular-weight LC molecules, different conformational states can coexist at single liquid crystalline phase; (3) the phase transition behavior of the azodendrimer is significantly affected by cooling rate because the molecular kinetics cannot follow too fast cooling.

Azobenzene-based molecular systems are used as photoreswitchable smart materials with applications in many areas, including designing surface orientational patterning of anisotropic molecules. It is important and challenging to probe the real-time photoresponsive behaviors of these systems, particularly the photodynamic processes from the mesoscopic to microscopic or macroscopic scales near surfaces. We report an unusual reversible interfacial wetting-dewetting switching of a dendrimer incorporating azobenzene moieties. The switching is accompanied by light-driven generation or extinction processes of the surface wetting nanostructures, which are composed of supramolecular polarly layered molecules. The resultant polar-nonpolar switching of the surface allows macroscopic wetting-dewetting and nonlinear optical responses. Our results provide unique insights into controlling transient structures of photoresponsive materials.

In this paper, we present a new photoswitchable viscoelastic material with liquid crystalline natures, which exhibits two types of nematic liquid crystalline phases and a crystal phase beneath the isotropic liquid. We present its light-triggered phase behaviors and photo-switchability of the viscoelastic properties.

We determine elastic constants K11, K22, and K33 in two diphenylacetylene-core-based liquid crystals with azo and ester linkages. As we have already reported (Adv. Mater. (2014) 26, 1918), K33 is extremely large (sub-nN) compared with K11 (pN) in the azo compound, since cybotactic smectic (Sm) clusters exist in whole the nematic (N) phase range. As a natural consequence, K22 is expected to be also large. We confirm that K22 is several tens pN, which is smaller than K33 but larger than K11 by one order of magnitude, K33>>K22>>K11. This is the first compound, which has a larger K22 than K11. In the ester compound, which has no clusters in the N phase, all the elastic constants are in a pN range, and are in the usual order, K33>K11>K22. It is also important to note that not only K33 and K22 but also K11 show a pretransitional increase when the N-SmC phase transition temperature is approached.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90° between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

In this paper, we review some results on our recent studies on photo-induced phenomena of liquid crystals (LCs) by means of interfaces decorated with a photo-responsive azobenzene dendrimer (azo-dendrimer). The azo-dendrimer molecules doped in a LC are spontaneously segregated from bulk and adsorbed onto substrate/LC or solvent/LC interfaces, and their photo-isomerization can bring about the so-called anchoring transition, i.e. reversible switching between homeotropic and planar alignment states of the bulk LC, when exposed to UV/VIS light. In addition to photoinduced anchoring transition in a LC cell, several interesting photo-induced phenomena through the azo-dendrimerdecorated interfaces have been reported, such as photo-induced transformation of the interior topological structures of nematic, cholesteric and smectic droplets, photo-mechanical motion of the micro particles dispersed in a nematic matrix, and optical assistance of the athermal anchoring transition with the aid of a perfluoropolymer surface. In addition to such phenomena, we also discuss the conditions of such photo-responsive interfaces in terms of the polar anchoring energy at the interface upon photo-isomerization under illumination of UV and/or VIS lights. The anisotropy of the polar anchoring energy was evaluated experimentally by means of Polarization Microscopy (POM), Dielectric Spectroscopy (DS), Second Harmonic Generation (SHG), and Attenuated Total Reflection Fourier Transform Infrared (ATR-IR) Spectroscopy, and theoretically based on the simple Rapini-Papoular model. We also demonstrate the continuous bulk orientation change by the photo-dynamic process through the fine control of the polar anchoring energy. Besides, the state-of-the-art video-rate atomic force microscopy (ν-AFM) was carried out to visualize the dynamics of such interfaces at a nano-meter scale.

A periodic stripe pattern is found in the nematic phase close to the smectic phase of photoresponsive achiral liquid-crystalline compounds. The origin of the stripe patterns can be ascribed to an extremely large bent elastic constant K33 . In addition, we succeeded in controlling the pattern by the following two methods: 1) the stripe disappears by a trans-cis photoisomerization upon UV light irradiation and reappears upon light termination, and 2) the stripe pattern is stabilized over the whole nematic phase, at approximately 10 °C, by polymerization of the compounds.

A surprisingly high bending elastic constant (K33 ) is obtained in a newly synthesized compound shown here. Mixtures containing a few percent of this compound confirm the influence of the unusual K33 values, and show an improved electro-optic response. The origin of the huge K33 is discussed based on the formation of a smectic cluster structure formed in the nematic phase.

We studied the relationship between the stability of the blue phase (BP) and the helical twisting power (HTP) of chiral molecules doped in a non-chiral bent-core liquid crystal. Contrary to common wisdom, HTP values were found not to directly affect BP stabilisation, i.e. a wide temperature range of BPs was obtained in mixtures containing chiral dopants with relatively small HTPs, whereas the mixtures containing high-HTP chiral dopants showed narrow BP temperature ranges. Moreover, in some cases, the narrow BPs even disappeared with increasing dopant concentration. In contrast, as expected, chiral dopant with large HTPs can easily induce BPs only by small dopant ratio; the minimum concentration necessary to induce the BPs is inversely proportional to an HTP value. As a cause of such unpredictable behaviour, packing effect between a host bent-core molecule and chiral dopants was discussed on the basis of the experimental observation of cybotactic clusters. Effect of UV irradiation for the BP stability was ...

A sequence of seven nematic phases has been observed in chiral mesogenic dimers, having odd number of carbon atoms in the spacer, thus a bent shape. The highest temperature phase is a chiral nematic (cholesteric) phase on heating or blue phases on cooling. The lowest temperature nematic phase expels the chiral twist and exhibits spontaneous bent–splay modulation.