新型含氟偶氮苯类液晶的合成和相变研究

设计并合成了一类新型的4′-（4″－n－烷氧基亚苯基乙炔基）4－n-乙氧基偶氮苯及其两个系列的氟代化合物,它们的相变行为通过差示扫描量热法和偏光显微镜进行了测试及观察,发现它们均是液晶化合物,都呈现向列相和近晶相,并且发现该类化合物的相变行为与氟原取代的数目与位置有着密切的关系。相比较不含氟的同类化合物,氟原子的引入降低了化合物的熔点和清亮点,如果两个氟原子对称分布在液晶分子长轴向的两侧有利于向列相的稳定性,相反分布于分子长轴一侧的两个氟原子有利于近晶相的稳定性／。     

对三氟甲氧基肉桂酸酯类液晶的合成与相变研究

设计并合成了一类新型的对三氟甲氧基肉桂酸酯类液晶,其相变行为通过DSC及偏光显微镜进行了观察和测试。化合物A呈现多种相态,而化合物B引入了四氟亚苯基,其相态数量减少,相变温度发生较大的变化。     

Controlling the Self‐Assembly of Periodic Defect Patterns in Smectic Liquid Crystal Films with Electric Fields

Large‐area periodic defect patterns are produced in smectic A liquid crystals confined between rigid plate electrodes that impose conflicting parallel and normal anchoring conditions, inducing the formation of topological defects. Highly oriented stripe patterns are created in samples thinner than 2 μm due to self‐assembly of linear defect domains with period smaller than 4 μm, whereas hexagonal lattices of focal conic domains appear for thicker samples. The pattern type (1d/2d) and period can be controlled at the nematic–smectic phase transition by applying an electric field, which confines the defect domains to a thin surface layer with thickness comparable to the nematic coherence length. The pattern morphology persists in the smectic phase even after varying the field or switching it off. Bistable, non‐equilibrium patterns are stabilized by topological constraints of the smectic phase that hinder the rearrangement of defects in response to field variations.     

Achieving Outstanding Mechanical Performance in Reinforced Elastomeric Composite Fibers Using Large Sheets of Graphene Oxide

A simple fiber spinning method used to fabricate elastomeric composite fibers with outstanding mechanical performance is demonstrated. By taking advantage of the large size of as‐prepared graphene oxide sheets (in the order of tens of micrometers) and their liquid crystalline behavior, elastomeric composite fibers with outstanding low strain properties have been fabricated without compromising their high strain properties. For example, the modulus and yield stress of the parent elastomer improved by 80‐ and 40‐fold, respectively, while maintaining the high extensibility of ～400% strain inherent to the parent elastomer. This outstanding mechanical performance was shown to be dependent upon the GO sheet size. Insights into how both the GO sheet size dimension and dispersion parameters influence the mechanical behavior at various applied strains are discussed.     

含三氟乙氧基的二苯乙炔类液晶的合成和相变研究

设计并合成了4个系列的新型含三氟乙氧基羰基的基芳香环上含氟或不含氟原子取代的二苯乙炔类液晶化合物,其相变行为通过偏光显微镜和差热分析进行了测试和观察,发现目标化合物都呈现很宽的近晶A相,当另一侧的碳氢链较短时,还有较窄的向列相存在,芳香环上引入的氟原子在有利于向列相的同时压缩了近晶相。     

Nematic Phases in 1,2,4‐Oxadiazole‐Based Bent‐Core Liquid Crystals: Is There a Ferroelectric Switching?

Four series of new 1,2,4‐oxadiazole derived bent‐core liquid crystals incorporating one or two cyclohexane rings are synthesized and investigated by optical polarizing microscopy, differential scanning calorimetry (DSC), X‐ray diffraction (XRD), electro‐optical, and dielectric investigations. All the compounds exhibit wide ranges of nematic phases composed of tilted smectic (SmC‐type) cybotactic clusters with strongly tilted aromatic cores (40–57°) and show a distinct peak in the current curves observed under a triangular wave field. Dielectric spectroscopy of aligned samples corroborates the previously proposed polar structure of the cybotactic clusters and the ferroelectric‐like polar switching of these nematic phases. Hence, it is shown that this is a general feature of the nematic phases of structurally different 3,5‐diphenyl‐1,2,4‐oxadiazole derivatives. In these uniaxial nematic phases there is appreciable local biaxiality and polar order in the cybotactic clusters. As a second point it is shown that electric field induced fan‐like textures, as often observed for the nematic phases of bent‐core liquid crystals, do not indicate the formation of a smectic phase, rather they represent special electro‐convection patterns due to hydrodynamic instabilities.     

Large Area Self‐Assembly of Nematic Liquid‐Crystal‐Functionalized Gold Nanorods

Fascinating nematic‐ and smectic‐like self‐assembled arrays are observed for gold nanorods partially capped with either laterally or terminally attached nematic liquid crystals upon slow evaporation of an organic solvent on TEM grids. These arrays can be manipulated and reoriented by applying an external magnetic field from quasi‐planar to vertical similar to a Fréedericksz transition of common organic nematic liquid crystals. Birefringence and thin film textures of these self‐assembled gold nanorod arrays observed by polarized optical microscopy are strongly reminiscent of common organic nematic liquid crystal textures between crossed polarizers and, additionally, support the formation of ordered liquid crystal‐like anisotropic superstructures. The ordering within these arrays is also confirmed in bulk samples using small angle X‐ray scattering (SAXS).     

Liquid‐Crystal Composites Composed of Photopolymerized Self‐Assembled Fibers and Aligned Smectic Molecules

A new liquid‐crystal composite, composed of photopolymerizable self‐assembled fibers and a smectic liquid crystal, and its photopolymerized composite have been prepared. The fibers oriented along the smectic layers are obtained by self‐assembly of an amino acid derivative with terminal methacryloyl groups in the smectic liquid crystal. The oriented fibrous structures are fixed by photopolymerization, resulting in the formation of microgrooves on the substrate surfaces. The aligned direction of the liquid‐crystalline molecules is changed to the direction along the fibers after thermal annealing. The patterning of liquid‐crystal alignment is achieved for these liquid‐crystal composites by patterned photopolymerization.     

Remote‐Controllable Molecular Knob in the Mesomorphic Helical Superstructures

A programed light‐responsive chiral liquid crystal (LC) containing four photochromic azobenzene moieties covalently connected to a central bicyclic chiral core (abbreviated as AZ₄ICD) is newly designed, precisely synthesized, and efficiently applied as a remote‐controllable molecular knob for the optically tunable thin film. First of all, phase evolutions and ordered structures of AZ₄ICD are systematically investigated by a combination of thermal, microscopic, scattering, and simulation techniques. Wide‐angle X‐ray diffractions of oriented AZ₄ICD samples indicate that the AZ₄ICD molecule itself basically forms layer structures: one is a low‐ordered chiral smectic A LC phase (SmA*) with 5.61 nm layer periodicity at high temperatures, and two highly ordered smectic crystal (SmCr₁ and SmCr₂) phases are subsequently formed at lower temperatures with the anticlinically tilted molecular packing structures. The helical superstructures of chiral nematic LC phase (N*) can be spontaneously constructed by doping AZ₄ICD chiral agents into the achiral nematic molecules. Due to the bent conformational geometry of AZ₄ICD, the thermal window of blue LC phase (BP) is expanded by stabilizing the double twisted cylindrical building blocks. Remote‐controllable phase transformations in the mesomorphic helical superstructures are demonstrated by tuning the wavelength of light.     

Segregated and Non-Settling Liquid Metal Elastomer via Jamming of Elastomeric Particles

Liquid metal elastomer (LME)—that is, liquid metal particles dispersed in elastomer—is a soft material that has useful electric, dielectric, and thermal properties. Two issues with LME are sought to be addressed: 1) the dense liquid metal (LM) particles can settle before curing of the elastomer, and 2) the LM particles are separated by a thin layer of insulating elastomer and therefore require some “mechanical sintering” to break this layer to create conductive paths. These issues are addressed using an LME containing elastic particles (LMEP). Elastic polydimethylsiloxane particles (PPs) and LM particles jam to prevent particle settling. Meanwhile, the PPs reduce the loading necessary to create conductive paths, thus decreasing the density and cost relative to LME. Surprisingly, the particles percolate into conductive paths prior to curing the LMEP but not in LME. The dielectric constant, electrical conductivity, and thermal conductivity of LMEPs are investigated by changing the volume fraction of LM particles, polydimethylsiloxane pre-polymer and PPs, and propose an LMEP with the optimal ratio. In addition, LMEP-based sensors and circuits are demonstrated for wearable electronics.     

4‐Cyanoresorcinol‐Based Bent‐Core Mesogens with Azobenzene Wings: Emergence of Sterically Stabilized Polar Order in Liquid Crystalline Phases

A new series of azobenzene containing bent‐core molecules incorporating 4‐cyanoresorcinol as the central core unit exhibiting cybotactic nematic, rectangular, columnar, and different types of tilted smectic (SmC) phases are synthesized. The mesophase behavior and phase structures are characterized in bulk and freely suspended films using a variety of experimental techniques. Depending on the chain length and temperature a series of different mesophases is observed in these compounds, ranging from cybotactic nematic via paraelectric SmC phases, polarization randomized SmC_sP_R phases to ferroelectric and antiferroelectric SmC phases, associated with increasing size and correlation length of the polar domains. Spontaneous formation of chiral domains is observed in the paraelectric SmC and the SmC_sP_R phases and discussed in relation with superstructural chirality, bend elastic constants, and surface effects.     

Ferroelectric Response and Induced Biaxiality in the Nematic Phase of Bent‐Core Mesogens

The still undiscovered fluid ferroelectric nematic phase is expected to exhibit a much faster and easier response to an external electric field compared to conventional ferroelectric smectic liquid crystals; therefore, the discovery of such a phase could open new avenues in electro‐optic device technology. Here, experimental evidence of a ferroelectric response to a switching electric field in a low molar mass nematic liquid crystal is reported and connected with field‐induced biaxiality. The fluid is made of bent‐core polar molecules and is nematic over a range of 120 °C. Combining repolarization current measurements, electro‐optical characterizations, X‐ray diffraction and computer simulations, ferroelectric switching is demonstrated and it is concluded that the response is due to field‐induced reorganization of polar cybotactic groups within the nematic phase. This work represents significant progress toward the realization of ferroelectric fluids that can be aligned at command with a simple electric field.     

Strain‐Responsive Polyurethane/PEDOT:PSS Elastomeric Composite Fibers with High Electrical Conductivity

It is a challenge to retain the high stretchability of an elastomer when used in polymer composites. Likewise, the high conductivity of organic conductors is typically compromised when used as filler in composite systems. Here, it is possible to achieve elastomeric fiber composites with high electrical conductivity at relatively low loading of the conductor and, more importantly, to attain mechanical properties that are useful in strain‐sensing applications. The preparation of homogenous composite formulations from poly­urethane (PU) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) that are also processable by fiber wet‐spinning techniques are systematically evaluated. With increasing PEDOT:PSS loading in the fiber composites, the Young's modulus increases exponentially and the yield stress increases linearly. A model describing the effects of the reversible and irreversible deformations as a result of the re‐arrangement of PEDOT:PSS filler networks within PU and how this relates to the electromechanical properties of the fibers during the tensile and cyclic stretching is presented.     

液晶的结构,缺陷与织构

液晶结构，缺陷与织构是相互关联的内容，液晶结构对称性的破坏产生缺陷，液晶缺陷的集合形成织构，而织构观察反过来又是鉴定液晶结构的重要手段，液晶结构，缺陷与织构即是液晶研究十分有趣的课题，同时对于液晶工业人员也是重要的，这篇文章液晶相分类，液晶结构，液晶相变等概念出发，应用拓扑分析，伏尔特拉过程，连续体弹性形变等理论，分析了向列相，胆甾相，近晶相（Ａ、Ｃ和Ｃ）液晶中，点，线和壁缺陷，包括向错，位错以及     

Simultaneous occurrence of phase conjugation and pulse shortening in stimulated scattering in liquid crystal mesophases

We have observed for the first time simultaneous occurrence of phase conjugation and pulse shortening in stimulated back scattering of nanosecond laser pulses from thin film of smectic and nematic liquid crystals, and from thick samples of isotropic cholesterics. Aberration correction capability and high compression ratio are obtained.     

棒状硫氰液晶的合成与表征

通过硫氰酸盐亲核取代反应合成了以苯甲酸联苯酯为液晶基元的硫氰棒状分子,一端尾链中的碳原子数为6、8和10。用偏光显微镜和差示扫描量热分析法对所合成的化合物进行了液晶相的表征,结果表明,这些硫氰化合物均表现出热致性近晶A相、向列相及尚未定性的液晶相M。随着尾链的增长,向列相温度区间变窄,清亮点降低。     

Highly Efficient and Water‐Insensitive Self‐Healing Elastomer for Wet and Underwater Electronics

Integrating self‐healing capabilities into soft electronic devices increases their durability and long‐term reliability. Although some advances have been made, the use of self‐healing electronics in wet and/or (under)water environments has proven to be quite challenging, and has not yet been fully realized. Herein, a new highly water insensitive self‐healing elastomer with high stretchability and mechanical strength that can reach 1100% and ≈6.5 MPa, respectively, is reported. The elastomer exhibits a high (>80%) self‐healing efficiency (after ≈ 24 h) in high humidity and/or different (under)water conditions without the assistance of an external physical and/or chemical triggers. Soft electronic devices made from this elastomer are shown to be highly robust and able to recover their electrical properties after damages in both ambient and aqueous conditions. Moreover, once operated in extreme wet or underwater conditions (e.g., salty sea water), the self‐healing capability leads to the elimination of significant electrical leakage that would be caused by structural damages. This highly efficient self‐healing elastomer can help extend the use of soft electronics outside of the laboratory and allow a wide variety of wet and submarine applications.     

Heat flow in thermally addressed liquid-crystal displays

Thermal addressing of both smectic and nematic liquid-crystal displays by melting has recently been demonstrated and is very promising. We present a theoretical and experimental investigation of the heat flow characteristics and suggest suitable combinations of power density and pulse length. In addition, we demonstrate a simple method of measuring the thermal diffusivity of the liquid crystal.     

An Adaptable Tough Elastomer with Moisture‐Triggered Switchable Mechanical and Fluorescent Properties

Smart materials with coupled optical and mechanical responsiveness to external stimuli, as inspired by nature, are of interest for the biomimetic design of the next generation of soft machines and wearable electronics. A tough polymer that shows adaptable and switchable mechanical and fluorescent properties is designed using a fluorescent lanthanide, europium (Eu). The dynamic Eu‐iminodiacetate (IDA) coordination is incorporated to build up the physical cross‐linking network in the polymer film consisting of two interpenetrated networks. Reversible disruption and reformation of Eu‐IDA complexation endow high stiffness, toughness, and stretchability to the polymer elastomer through energy dissipation of dynamic coordination. Water that binds to Eu³⁺ ions shows an interesting impact simultaneously on the mechanical strength and fluorescent emission of the Eu‐containing polymer elastomer. The mechanical states of the polymer, along with the visually optical response through the emission color change of the polymer film, are reversibly switchable with moisture as a stimulus. The coupled response in the mechanical strength and emissive color in one single material is potentially applicable for smart materials requiring an optical readout of their mechanical properties.     

Mesoporous Piezoelectric Polymer Composite Films with Tunable Mechanical Modulus for Harvesting Energy from Liquid Pressure Fluctuation

Harvesting mechanical energy from biological systems possesses great potential for in vivo powering implantable electronic devices. In this paper, a development of flexible piezoelectric nanogenerator (NG) is reported based on mesoporous poly(vinylidene fluoride) (PVDF) films. Monolithic mesoporous PVDF is fabricated by a template‐free sol–gel‐based approach at room temperature. By filling the pores of PVDF network with poly(dimethylsiloxane) (PDMS) elastomer, the composite's modulus is effectively tuned over a wide range down to the same level of biological systems. A close match of the modulus between NG and the surrounding biological component is critical to achieve practical integration. Upon deformation, the composite NG exhibits appreciable piezoelectric output that is comparable to or higher than other PVDF‐based NGs. An artificial artery system is fabricated using PDMS with the composite NG integrated inside. Effective energy harvesting from liquid pressure fluctuation (simulating blood pressure fluctuation) is successfully demonstrated. The simple and effective approach for fabricating mesoporous PVDF with tunable mechanical properties provides a promising route toward the development of self‐powered implantable devices.