Bioinspired MXene-Based Soft Actuators Exhibiting Angle-Independent Structural Color

In nature,many living organisms exhibiting unique structural coloration and soft-bodied actuation have inspired scientists to develop advanced structural colored soft actuators toward biomimetic soft robots.However,it is challenging to simultaneously biomimic the angle-independent structural color and shape-morphing capabilities found in the plum-throated cotinga flying bird.Herein,we report biomimetic MXene-based soft actuators with angle-independent structural color that are fabricated through controlled self-assembly of colloidal SiO_(2) nanoparticles onto highly aligned MXene films followed by vacuum-assisted infiltration of polyvinylidene fluoride into the interstices.The resulting soft actuators are found to exhibit brilliant,angle-independent structural color,as well as ultrafast actuation and recovery speeds(a maximum curvature of 0.52 mm−1 can be achieved within 1.16 s,and a recovery time of~0.24 s)in response to acetone vapor.As proof-of-concept illustrations,structural colored soft actuators are applied to demonstrate a blue gripper-like bird’s claw that can capture the target,artificial green tendrils that can twine around tree branches,and an artificial multicolored butterfly that can flutter its wings upon cyclic exposure to acetone vapor.The strategy is expected to offer new insights into the development of biomimetic multifunctional soft actuators for somatosensory soft robotics and next-generation intelligent machines.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.

Ionic Elastomers for Electric Actuators and Sensors

In the past decades,ion conductive polymers and elastomers have drawn worldwide attention for their advanced functions in batteries,electroactive soft robotics,and sensors.Stretchable ionic elastomers with dispersed soft ionic moieties such as ionic liquids have gained remarkable attention as soft sensors,in applications such as the wearable devices that are often called electric skins.A considerable amount of research has been done on ionic-elastomer-based strain,pressure,and shear sensors;however,to the best of our knowledge,this research has not yet been reviewed.In this review,we summarize the materials and performance properties of engineered ionic elastomer actuators and sensors.First,we review three classes of ionic elastomer actuators—namely,ionic polymer metal composites,ionic conducting polymers,and ionic polymer/carbon nanocomposites—and provide perspectives for future actuators,such as adaptive four-dimensional(4D)printed systems and ionic liquid crystal elastomers(iLCEs).Next,we review the state of the art of ionic elastomeric strain and pressure sensors.We also discuss future wearable strain sensors for biomechanical applications and sports performance tracking.Finally,we present the preliminary results of iLCE sensors based on flexoelectric signals and their amplification by integrating them with organic electrochemical transistors.

Flexoelectric-effect-based light waveguide liquid crystal display for transparent display

We report a light waveguide liquid crystal display(LCD) based on the flexoelectric effect. The display consists of two parallel flat substrates with a layer of flexoelectric liquid crystal sandwiched between them. A light-emitting diode(LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display by total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state due to flexoelectric interaction and becomes scattering. The incident light is deflected from the waveguide mode and comes out of the viewing side of the display. We achieved thin-film-transistor active matrix compatible driving voltage by doping liquid crystal dimers with large flexoelectric coefficients. The light waveguide LCD does not use polarizers as in conventional LCDs. It has an ultrahigh transmittance near 90% in the voltage-off state. It is very suitable for transparent display, which can be used for head-up display and augmented reality display.

Polymerization enabled reduction of the electrically induced birefringence change in nematic liquid crystals

Electric fields modify the optical properties of nematic liquid crystals(NLCs) by changing the nematic molecular orientation or order parameters, which enables electro-optic applications of NLCs. However, the field-induced optic change is undesirable in some cases. Here, we experimentally demonstrate that polymer stabilization weakens the birefringence change of NLCs caused by the nanosecond electrically modified order parameter effect. The birefringence change is reduced by 65% in the NLC doped with 25% reactive monomer, which is polymerized close to the nematic-to-isotropic phase transition. This technique could be used in liquid crystal devices where the birefringence change is unfavored.

等离子体处理过的基板上液晶平行取向的两种模式

我们提出了一种用于液晶盒的新取向工艺,可以得到0或非0的预倾角。这项工艺是用定向的等离子体流倾斜辐照基板。我们用一个阳极层发射器(anodelagerthruster)作为等离子体辐射源,以产生层状的等离子体流。它适合于处理大面积基板,可以处理有机(聚合物)和无机(玻璃,ITO)层。等离子体流辐照可以得到两种类型的液晶取向:(1)最可及(择优)取向轴位于离子束方向和基板法线组成的入射平面上;(2)最可及取向轴垂直于入射面。随着照射总剂量的增加,取向方向可以从类型(1)向类型(2)转变。在第一种取向模式中,可以通过改变工艺参数,如入射角、离子流密度和离子能等来改变预倾角。第二种取向模式的特征是预倾角为0。第一种模式的方位锚泊能系数相对较弱(W=10-3 Erg/cm2),而第二种类型锚泊能很强(W>10-1 Erg/cm2),与摩擦聚合物基板相当。两种模式的取向特征可以用来产生满足所需参数的取向,和构图(pattern)液晶盒基板。这种工艺方法可以克服传统摩擦工艺的某些缺点。

Curvature-induced lipid segregation

We investigate how an externally imposed curvature influences lipid segregation on two-phase-coexistent membranes.We show that the bending-modulus contrast of the two phases and the curvature act together to yield a reduced effective line tension.On largely curved membranes,a state of multiple domains(or rafts) forms due to a mechanism analogous to that causing magnetic-vortex formation in type-II superconductors.We determine the criterion for such a multi-domain state to occur;we then calculate respectively the size of the domains formed on cylindrically and spherically curved membranes.

Determining the imaging plane of a retinal capillary layer in adaptive optical imaging

Even in the early stage,endocrine metabolism disease may lead to micro aneurysms in retinal capillaries whose diameters are less than 10 μm.However,the fundus cameras used in clinic diagnosis can only obtain images of vessels larger than 20 μm in diameter.The human retina is a thin and multiple layer tissue,and the layer of capillaries less than10 μm in diameter only exists in the inner nuclear layer.The layer thickness of capillaries less than 10 μm in diameter is about 40 μm and the distance range to rod&cone cell surface is tens of micrometers,which varies from person to person.Therefore,determining reasonable capillary layer(CL) position in different human eyes is very difficult.In this paper,we propose a method to determine the position of retinal CL based on the rod&cone cell layer.The public positions of CL are recognized with 15 subjects from 40 to 59 years old,and the imaging planes of CL are calculated by the effective focal length of the human eye.High resolution retinal capillary imaging results obtained from 17 subjects with a liquid crystal adaptive optics system(LCAOS) validate our method.All of the subjects' CLs have public positions from 127 μm to 147 μm from the rod&cone cell layer,which is influenced by the depth of focus.

Analytic solutions of the normal modes and light transmission of a cholesteric liquid crystal cell

Cholesteric liquid crystals,consisting of chiral molecules,form self-assembled periodic structures exhibiting a photonic bandgap.Their selective reflectivity makes them well suited for a variety of applications;their optical response is therefore of considerable interest.The reflectance and transmittance of finite cholesteric cells is usually calculated numerically.Evanescent modes in the bandgap make the calculations challenging;existing matrix propagation methods cannot describe the reflection and transmission coefficients of thick cholesteric cells accurately.Here we present analytic solutions for the electromagnetic fields in cholesteric cells of finite thickness,and use them to calculate the transmission and reflection spectra.The use of analytic solutions allows for the accurate description of arbitrarily thick cholesteric cells,which would not be possible with only direct numerical methods.

Reverse mode switching of the random laser emission in dye doped liquid crystals under homogeneous and inhomogeneous electric fields

We report the observation of electric field induced random lasing in a dye doped liquid crystal system. This was achieved by using a liquid crystal host with negative dielectric anisotropy doped with laser dye PM 597 in a 75 μm cell with a homeotropic alignment layer. In the absence of an applied field, only amplified spontaneous emission was observed since the liquid crystal orientation was uniform. However, application of a field resulted in a fieldinduced planar-like configuration with local nonuniformity in liquid crystal orientation. This led to random lasing in the energized state(voltage greater than a transition threshold). The onset of lasing occurs by application of either a spatially homogenous or a spatially inhomogeneous electric field across the liquid crystal. The characteristics of the emission spectra as a function of different(i) dye concentration and(ii) applied voltage were investigated using nanosecond pulsed laser excitation at 532 nm. The effects of using an inhomogeneous field were compared to the use of a homogenous field and reported. It is shown that the spatial configuration can be used to alter the emission spectra of the system. The work is used to suggest a new configuration, referred to here as"reverse mode," for liquid crystal-based random lasers. This new configuration may provide additional avenues for their use in commercial devices.

Dielectric properties of ternary composites of triblock polymer surfactant, liquid crystal and organic solvent

Dielectric spectroscopy,at room temperature(20℃),is used to study the dielectric response of ternary mixtures of commercial nematic liquid crystal mixtures E7 and E33,an organic solvent N-Methyl-2-Pyrrolidone(NMP)and a triblock polymers in the frequency range from 0.01Hz to 1MHz.The results indicate a dielectric relaxation in the hectohertz region.Individually,both E7 and NMP have rather large low frequency conductivities;however,the low frequency(0.01–10Hz)behavior of the mixtures has no such behavior.We attribute this behavior to an ion getter effect of the triblock polymer surfactant.Optimized ternary mixtures obtain a real dielectric constant near 230,and loss tangent less than 0.05 at frequencies near 10mHz.

Multiple-object Shack–Hartmann wavefront sensor design for a wide field of view on the retina

In order to detect the aberration from a wide field of view(FOV) on the retina with adaptive optics, we present a multiple-object Shack–Hartmann wavefront sensor(MOSHWFS) design. The simulated results indicate that the wavefront from our MOSHWFS can be reconstructed for multiple objects, and the measurement error can be less than λ∕7 with an MOSHWFS with an FOV of 6.7°, for maximum eye aberration. The experimental result with two objects indicates that the measurement error can be less than λ∕14, with the root mean square of the reference wavefront as 0.798λ and 0.895λ, respectively.

A high mobility air-stable n-type organic small molecule semiconductor with high UV-visible-to-NIR photoresponse

An organic semiconductor with high carrier mobility and efficient light absorption over a wide spectral range is of the most important yet challenging material for constructing a broadband responsive organic photodetector.However,the development of such organic semiconductors,especially for air-stable n-type organic small molecule semiconductors,is still at an early stage.Here we report the fabrication of high-performance n-type semiconducting crystalline nanosheets and the development of air-stable field-effect transistors,phototransistors,with high response over a broad spectrum.The n-type small molecule semiconductor is assembled into a crystalline nanosheet based on the solvent-phase interfacial self-assembly method.N-type field-effect transistors with high electron mobility are fabricated and their electrical performances exhibit excellent air stability.Impressively,the demonstrated phototransistors exhibit an ultrahigh responsivity over a wide spectral range from 365 to 940 nm,with a maximum photoresponsivity of 9.2×10^(5) AW-1 and specific detectivity of 5.26×10^(13) Jones,which is the best performance among the reported n-type organic small molecule-based phototransistors.

Stretchable and self-healable spoof plasmonic meta-waveguide for wearable wireless communication system

Microwave transmission lines in wearable systems are easily damaged after frequent mechanical deformation,posing a severe threat to wireless communication.Here,we report a new strategy to achieve stretchable microwave transmission lines with superior reliability and durability by integrating a self-healable elastomer with serpentine-geometry plasmonic meta-waveguide to support the spoof surface plasmon polariton(SSPP).After mechanical damage,the self-healable elastomer can autonomously repair itself to maintain the electromagnetic performance and mechanical strength.Meanwhile,the specially designed SSPP structure exhibits excellent stability and damage resistance.Even if the self-healing process has not been completed or the eventual repair effect is not ideal,the spoof plasmonic meta-waveguide Can still maintain reliable performance.Self-healing material enhances strength and durability,while the SSPP improves stability and gives more tolerance to the self-healing process.Our design coordinates the structural design with material synthesis to maximize the advantages of the SSPP and self-healing material,signifcantly improving the relability and durability of stretchable microwave transmission lines.We also perform communication quality experiments to demonstrate the potential of the proposed meta-waveguide as interconnects in future body area network systems.

Circularly polarized luminescent self-organized helical superstructures:From materials and stimulus-responsiveness to applications

Circularly polarized luminescence(CPL)has gained considerable attention in various systems and has rapidly developed into an emerging research field.To meet the needs of actual applications in diverse fields,a high luminescence dissymmetry factor(glum)and tunable optical performance of CPL would be the most urgent pursuit for researchers.Accordingly,many emerging CPL materials and various strategies have been developed to address these critical issues.Emissive cholesteric liquid crystals(CLCs),that is,luminescent self-organized helical superstructures,are considered to be ideal candidates for constructing CPL-active materials,as they not only exhibit high glum values,but also enable flexible optical control of CPL.This review mainly summarizes the characteristics of CPL based on CLCs as the bulk phase doped with different emitters,including aggregated induced emission molecules,conventional organic small molecules,polymer emitters,metal-organic complex emitters,and luminescent nanoparticles.In addition,the recent significant progress in stimulus-responsive CPL based on emissive CLCs in terms of several types of stimuli,including light,electricity,temperature,mechanical force,and multiple stimuli is presented.Finally,a short perspective on the opportunities and challenges associated with CPL-active materials based on the CLC field is provided.This review is anticipated to offer new insights and guidelines for developing CLC-based CPL-active materials for broader applications.

Electrically tunable helicity of cholesteric heliconical superstructure [Invited]

The dynamic manipulation of the helicity in a cholesteric helical superstructure could enable precise control over its physical and chemical properties, thus opening numerous possibilities for exploring multifunctional devices.When cholesteric material satisfies the sufficiently small bending elastic effect, an electrically induced deformation named the cholesteric heliconical superstructure is formed. Through theoretical and numerical analysis, we systematically studied the tunable helicity of the heliconical superstructure, including the evolution of the corresponding oblique angle and pitch length. To further confirm the optical properties, Berreman’s 4 × 4 matrix method was employed to numerically analyze the corresponding structure reflection under the dual stimuli of chirality and electric field.

具有超高抗疲劳性能的液态金属增强型液晶弹性体材料

液晶弹性体材料内在的低交联密度特性导致其抗疲劳性能差,严重影响了此类材料在工业上的应用前景.本文报道了一种液态金属增强型液晶弹性体材料,通过将5 wt%液态金属纳米微粒(平均直径:约195 nm)引入液晶弹性体网络,可以显著增强液晶弹性体复合材料的力学性能,特别是超高的抗疲劳性能.该复合材料能够在大应变范围(应变幅度范围高达70%)内承受10,000次拉伸循环和2000次连续可逆致动形变,同时展现出大致动应变(最大致动应变:55%)、大致动应力(1.13 MPa)、完全可逆的热/光驱动性和常温下的自修复功能.该液态金属增强型液晶弹性体材料有望在高载荷致动器领域实现工业化应用.