Large-area display textiles integrated with functional systems.

Displays are basic building blocks of modern electronics1,2. Integrating displays into textiles offers exciting opportunities for smart electronic textiles-the ultimate goal of wearable technology, poised to change the way in which we interact with electronic devices3-6. Display textiles serve to bridge human-machine interactions7-9, offering, for instance, a real-time communication tool for individuals with voice or speech difficulties. Electronic textiles capable of communicating10, sensing11,12 and supplying electricity13,14 have been reported previously. However, textiles with functional, large-area displays have not yet been achieved, because it is challenging to obtain small illuminating units that are both durable and easy to assemble over a wide area. Here we report a 6-metre-long, 25-centimetre-wide display textile containing 5 × 105 electroluminescent units spaced approximately 800 micrometres apart. Weaving conductive weft and luminescent warp fibres forms micrometre-scale electroluminescent units at the weft-warp contact points. The brightness between electroluminescent units deviates by less than 8 per cent and remains stable even when the textile is bent, stretched or pressed. Our display textile is flexible and breathable and withstands repeated machine-washing, making it suitable for practical applications. We show that an integrated textile system consisting of display, keyboard and power supply can serve as a communication tool, demonstrating the system's potential within the 'internet of things' in various areas, including healthcare. Our approach unifies the fabrication and function of electronic devices with textiles, and we expect that woven-fibre materials will shape the next generation of electronics.

Hybrid Fabrication of Prestrain-Locked Acrylic Dielectric Elastomer Thin Films and Multilayer Stacks.

Dielectric elastomers based on commercial acrylic dielectric elastomers (VHB adhesive films) are widely investigated for soft actuators due to their large electrically driven actuation strain and high work density. However, the VHB films require prestretching to overcome electromechanical instability, which adds fabrication complexity. In addition, their high viscoelasticity leads to a low response speed. Interpenetrated polymer networks (IPNs) are developed to lock the prestrain in VHB films, resulting in free-standing films that are capable of large-strain actuation. In this work, a prestrain-locked high-performance dielectric elastomer thin film (VHB-IPN-P) by introducing 1,6-hexanediol diacrylate to create an IPN in the VHB network and a plasticizer to enhance the actuation speed is reported. VHB-IPN-P based actuators exhibit stable actuation at 60% strain up to 10 Hz and reach a peak energy density of 102 J kg⁻1 . In addition, a hybrid process is also developed for the fabrication of multilayer stacks of VHB-IPN-P with strong inter-layer bonding and structural integrity. Four-layer stacks fabricated preserve the strain and energy density of single-layer VHB-IPN-P films but with linearly scaled force and work output.

Dielectric Elastomer Artificial Muscle: Materials Innovations and Device Explorations.

Creating an artificial muscle has been one of the grand challenges of science and engineering. The invention of such a flexible, versatile, and power efficient actuator opens the gate for a new generation of lightweight, highly efficient, and multifunctional robotics. Many current artificial muscle technologies enable low-power mobile actuators, robots that mimic efficient and natural forms of motion, autonomous robots and sensors, and lightweight wearable technologies. They also have serious applications in biomedical devices, where biocompatibility, from a chemical, flexibility, and force perspective, is crucial. It remains unknown which material will ultimately form the ideal artificial muscle. Anything from shape memory alloys (SMAs) to pneumatics to electroactive polymers (EAPs) realize core aspects of the artificial muscle goal. Among them, EAPs most resemble their biological counterparts, and they encompass both ion-infusion and electric field based actuation mechanisms. Some of the most investigated EAPs are dielectric elastomers (DEs), whose large strains, fracture toughness, and power-to-weight ratios compare favorably with natural muscle. Although dielectric elastomer actuators (DEAs) only entered the artificial muscle conversation in the last 20 years, significant technological progress has reflected their high potential. Research has focused on solving the core issues surrounding DEAs, which includes improving their operational ranges with regard to temperature and voltage, adding new functionality to the materials, and improving the reliability of the components on which they depend. Mechanisms designed to utilize their large-strain actuation and low stiffness has also attracted attention. This Account covers important research by our group and others in various avenues such as decreasing viscoelastic losses in typical DE materials, increasing their dielectric constant, and countering electromechanical instability. We also discuss variable stiffness polymers, specifically bistable electroactive polymers, which, notably, open DEAs to structural applications typically unattainable for soft-actuator technologies. Furthermore, we explore advancements related to highly compliant and transparent electrodes, a crucial component of DEAs capable of achieving high actuation strain. We then cover noteworthy applications, including several novel devices for soft robotics and microfluidics, and how those applications fit within other major developments in the field. Finally, we conclude with a discussion of the remaining challenges facing current DEA technology and speculate on research directions that may further advance DE-based artificial muscles as a whole. This Account serves as a stepping stone into the field of EAPs, which, through the work of researchers worldwide, are positioned as a potential challenger to conventional actuator technologies.

A Phase-Changing Polymer Film for Broadband Smart Window Applications.

Smart windows (SWs) with tunable opacity are sought to regulate solar-irradiation and privacy protection. A new smart window material based on a phase-changing polymer that can be reversibly switched between a semicrystalline, opaque state and an amorphous, transparent state is introduced. The polymer film is a network of the phase-changing poly(stearyl acrylate) crosslinked with a poly(ethylene oxide) oligomer. The two constituent polymers show strong phase separation. The transmission switching of the resulting copolymer film is resulted from the combination of three different mechanisms: reversible phase changing of the poly(stearyl acrylate) component, phase separation between the two distinct constituent polymers, and a large change of refractive index of the phase-changing polymer during the amorphous-to-semicrystalline transition. The opaqueness switching can be reversed and repeated for more than 500 cycles of heating and cooling. A silver nanowire (AgNW)-based transparent heater is combined with the SW film to control the semicrystalline-to-amorphous phase transition. The resulting smart window exhibits a high infrared transmittance modulation (ΔTIR ) of 80.4% and solar transmittance modulation (ΔTsolar ) of 70.2%, which significantly outperform existing thermochromic smart windows.

Morphological/nanostructural control toward intrinsically stretchable organic electronics.

The development of intrinsically stretchable electronics poses great challenges in synthesizing elastomeric conductors, semiconductors and dielectric materials. While a wide range of approaches, from special macrostructural engineering to molecular synthesis, have been employed to afford stretchable devices, this review surveys recent advancements in employing various morphological and nanostructural control methods to impart mechanical flexibility and/or to enhance electrical properties. The focus will be on (1) embedding percolation networks of one-dimensional conductive materials such as metallic nanowires and carbon nanotubes in an elastomer matrix to accommodate large external deformation without imposing a large strain along the one-dimensional materials, (2) design strategies to achieve intrinsically stretchable semiconductor materials that include direct blending of semiconductors with elastomers and synthesizing semiconductor polymers with appropriate side chains, backbones, cross-linking networks, and flexible blocks, and (3) employing interpenetrating polymer networks, bottlebrush structures and introducing inclusions in stretchable polymeric dielectric materials to improve electrical performance. Moreover, intrinsically stretchable electronic devices based on these materials, such as stretchable sensors, heaters, artificial muscles, optoelectronic devices, transistors and soft humanoid robots, will also be described. Limitations of these approaches and measures to overcome them will also be discussed.

Electronic Muscles and Skins: A Review of Soft Sensors and Actuators.

This article reviews several classes of compliant materials that can be utilized to fabricate electronic muscles and skins. Different classes of materials range from compliant conductors, semiconductors, to dielectrics, all of which play a vital and cohesive role in the development of next generation electronics. This paper covers recent advances in the development of new materials, as well as the engineering of well-characterized materials for the repurposing in applications of flexible and stretchable electronics. In addition to compliant materials, this article further discusses the use of these materials for integrated systems to develop soft sensors and actuators. These new materials and new devices pave the way for a new generation of electronics that will change the way we see and interact with our devices for decades to come.

Dissipative performance of dielectric elastomers under various voltage waveforms.

The actuation performance of dielectric elastomers (DEs) is affected by dissipation. In the present article, an analytical model is developed to investigate the dissipative performance of DEs by considering viscoelasticity and leakage current. Various voltage waveforms, such as DC voltage, square voltage, stepwise DC voltage, ramp voltage, sawtooth voltage, and triangular voltage, were applied to explore the dissipative performance of DEs. The DEs with diverse moduli and viscoelasticity intensities were also analyzed by comparing the different dissipative performances. Numerical calculations were employed to evaluate the dissipative behavior of DEs. When the value of the applied voltage is maintained invariable, the stretch gradually creeps, and the total current from the battery and the leakage current approach each other eventually. When the applied voltage varies linearly, the stretch deforms dramatically, and then the total current from the battery is much larger than the leakage current.

Atmospheric and Aqueous Deposition of Polycrystalline Metal Oxides Using Mist-CVD for Highly Efficient Inverted Polymer Solar Cells.

Large scale, cost-effective processing of metal oxide thin films is critical for the fabrication of many novel thin film electronics. To date, however, most of the reported solution-based techniques require either extended thermal anneals or additional synthetic steps. Here we report mist chemical vapor deposition as a solution-based, readily scalable, and open-air method to produce high-quality polycrystalline metal oxide thin films. Continuous, smooth, and conformal deposition of metal oxide thin films is achieved by tuning the solvent chemistry of Leidenfrost droplets to promote finer control over the surface-local dissociation process of the atomized zinc-bearing precursors. We demonstrate the deposited ZnO as highly efficient electron transport layers for inverted polymer solar cells to show the power of the approach. A highest efficiency of 8.7% is achieved with a fill factor of 73%, comparable to that of conventional so-gel ZnO, which serves as an indication of the efficient vertical transport and electron collection achievable using this material.

Coupled nonlinear oscillation and stability evolution of viscoelastic dielectric elastomers.

This article describes the development of an analytical model to study the coupled nonlinear oscillation and stability evolution of viscoelastic dielectric elastomers (DEs) under non-equibiaxial tensile forces by utilizing the method of virtual work. Numerically calculated results are employed to predict this nonlinear dynamic behavior. The resonant frequency (where the amplitude-frequency response curve peaks) and the amplitude-frequency response of the deformation in both in-plane directions are tuned by varying the values of tensile force. The oscillation response in the two in-plane directions exhibits strong nonlinearity and coupling with each other, and is tuned by the changing tensile forces under a specific excitation frequency. By varying the values of tensile forces, the dynamic viscoelastic creep in a certain in-plane direction can be eliminated. Phase diagrams and Poincaré maps under several values of tensile forces are utilized to study the stability evolution of the DE system under non-equibiaxial tensile forces.

Nanocomposite Scintillators Loaded With Hafnium Oxide and Phosphorescent Host and Guest for Gamma Spectroscopy.

Gamma sensitive plastic scintillators are of critical importance in the fields of nuclear nonproliferation, medical imaging, and high energy physics. However, there is often a trade-off between high light yield and high loading of high-Z components, both of which play an essential role in gamma ray detection. This work takes advantage of triplet exciton harvesting to increase gamma light yield by utilizing 1,3-di(9H-carbazol-9-yl)benzene and 9,9-dimethyl-9H-fluorene as triplet hosts to facilitate Dexter energy transfer to bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrPic), a blue light emitting phosphorescent dye. A plastic scintillator containing 20 wt % MF, 10 wt % mCP, and 2 wt % FIrPic has a high gamma light yield of 14 800 Ph/MeV. Incorporating 20-35 wt % hafnium oxide nanoparticles into this organic matrix results in nanocomposites that demonstrate a gamma photopeak energy resolution of 6.4-9.7% at 662 keV while still retaining a high gamma light yield between 8800 and 10 800 Ph/MeV.

Height-renderable morphable tactile display enabled by programmable modulation of local stiffness in photothermally active polymer.

Reconfigurable tactile displays are being used to provide refreshable Braille information; however, the delivered information is currently limited to an alternative of Braille because of difficulties in controlling the deformation height. Herein, we present a photothermally activated polymer-bilayer-based morphable tactile display that can programmably generate tangible three-dimensional topologies with varying textures on a thin film surface. The morphable tactile display was composed of a heterogeneous polymer structure that integrated a stiffness-tunable polymer into a light-absorbing elastomer, near-infra-red light-emitting diode (NIR-LED) array, and small pneumatic chamber. Topological expression was enabled by producing localized out-of-plane deformation that was reversible, height-adjustable, and latchable in response to light-triggered stiffness modulation at each target area under switching of stationary pneumatic pressure. Notably, the tactile display could express a spatial softness map of the latched topology upon re-exposing the target areas to modulated light from the NIR-LED array. We expect the developed tactile display to open a pathway for generating high-dimensional tactile information on electronic devices and enable realistic interaction in augmented and virtual environments.

E-beam deposited Ag-nanoparticles plasmonic organic solar cell and its absorption enhancement analysis using FDTD-based cylindrical nano-particle optical model.

We report the plasmon-assisted photocurrent enhancement in Ag-nanoparticles (Ag-NPs) embedded PEDOT:PSS/P3HT:PCBM organic solar cells, and systematically investigate the causes of the improved optical absorption based on a cylindrical Ag-NPs optical model which is simulated with a 3-Dimensional finite difference time domain (FDTD) method. The proposed cylindrical Ag-NPs optical model is able to explain the optical absorption enhancement by the localized surface plasmon resonance (LSPR) modes, and to provide a further understanding of Ag-NPs shape parameters which play an important role to determine the broadband absorption phenomena in plasmonic organic solar cells. A significant increase in the power conversion efficiency (PCE) of the plasmonic solar cell was experimentally observed and compared with that of the solar cells without Ag-NPs. Finally, our conclusion was made after briefly discussing the electrical effects of the fabricated plasmonic organic solar cells.

Intrinsically stretchable transparent electrodes based on silver-nanowire-crosslinked-polyacrylate composites.

Stretchable transparent composites have been synthesized consisting of a silver nanowire (AgNW) network embedded in the surface layer of a crosslinked poly(acrylate) matrix. The interpenetrating networks of AgNWs and the crosslinked polymer matrix lead to high surface conductivity, high transparency, and rubbery elasticity. The presence of carboxylic acid groups on the polymer chains enhances the bonding between AgNWs and the polymer matrix, and further increases the stretchability of the composites. The sheet resistance of the composite electrode increases by only 2.3 times at 50% strain. Repeated stretching to 50% strain and relaxation only causes a small increase of the sheet resistance after 600 cycles. The morphology of the composites during reversible stretching and relaxation has been investigated to expound the conductivity changes.

Efficient white polymer light-emitting diodes employing a silver nanowire-polymer composite electrode.

White polymer phosphorescent light-emitting diodes have been fabricated employing silver nanowire (AgNW)-polymer composite substrates. Solution processing is used to form all the layers in the devices, except for the cathode, for potentially low fabrication cost. The current efficiency in the front viewing direction is 20.3 cd A(-1) for devices comprising two complementary dopants (bis[(4,6-difluorophenyl)-pyridinato-N,C(2)] (picolinato)Ir(iii) (FIrpic) with sky blue emission and bis(1-phenylisoquinoline)(acetylacetonate) (Ir(piq)) for red emission). The efficiency is 42.3 cd A(-1) at 4000 cd cm(-2) for devices comprising the three primary colors (FIrpic, Ir(piq), and tris(2-(4-tolyl)pyridinato-N,C(2)) (Ir(mppy)(3)), with green emission). These values are, respectively, 35% and 41% higher than those of control devices fabricated on indium tin oxide (ITO) coated on glass substrates. The enhanced current efficiency is attributed to enhanced light out-coupling thanks to light scattering by the silver nanowires embedded in the transparent composite electrode.

Stiffness Variable Polymers Comprising Phase-Changing Side-Chains: Material Syntheses and Application Explorations.

Stiffness variable materials have been applied in a variety of engineering fields that require adaptation, automatic modulation, and morphing because of their unique property to switch between a rigid, load-bearing state and a soft, compliant state. Stiffness variable polymers comprising phase-changing side-chains (s-SVPs) have densely grafted, highly crystallizable long alkyl side-chains in a crosslinked network. Such a bottlebrush network-like structure gives rise to rigidity modulation as a result of the reversible crystallization and melting of the side chains. The corresponding modulus changes can be more than 1000-fold within a narrow temperature span, from ≈102  MPa to ≈102  kPa or lower. Other important properties of the s-SVP, such as stretchability, optical transmittance, and adhesion, can also be altered. This work reviews the underlying molecular mechanisms in the s-SVP's, discusses the material's structure-property relationship, and summarizes important applications explored so far, including reversible shape transformation, bistable electromechanical transduction, optical modulation, and reversible adhesion.

Structures and Materials in Stretchable Electroluminescent Devices.

Stretchable electroluminescent (EL) devices are obtained by partitioning a large emission area into areas specifically for stretching and light-emission (island-bridge structure). Buckled and textile structures are also shown effective to combine the conventional light emitting diode fabrication with elastic substrates for structure-enabled stretchable EL devices. Meanwhile, intrinsically stretchable EL devices which are characterized with uniform stretchability down to microscopic scale are relatively less developed but promise simpler device structure and higher impact resistance. The challenges in fabricating intrinsically stretchable EL devices with high and robust performance are in many facets, including stretchable conductors, emissive materials, and compatible processes. For the stretchable transparent electrode, ionically conductive gel, conductive polymer coating, and conductor network in surface of elastomer are all proven useful. The stretchable EL materials are currently limited to conjugated polymers, conjugated polymers with surfactants and ionic conductors added to boost stretchability, and phosphor particles embedded in elastomer matrices. These emissive materials operate under different mechanisms, require different electrode materials and fabrication processes, and the corresponding EL devices face distinctive challenges. This review aims to provide a basic understanding of the materials meeting both the mechanical and electronic requirements and important techniques to fabricate the stretchable EL devices.

Design rules for time of flight Positron Emission Tomography (ToF-PET) heterostructure radiation detectors.

Despite the clinical acceptance of ToF-PET, there is still a gap between the technology's performance and the end-user's needs. Core to bridging this gap is the ability to develop radiation detectors combining a short attenuation length and a sub-nanosecond time response. Currently, the detector of choice, Lu2SiO5:Ce3+ single crystal, is not selected for its ability to answer the performance needs, but as a trade-off between requirements and availability. To bypass the current performance limitations, in particular restricted time response, the concept of the heterostructured detector has been proposed. The concept aims at splitting the scintillation mechanisms across two materials, one acting primarily as an absorber and one as an ultra-fast emitter. If the concept has attracted the interest of the medical and material communities, little has been shown in terms of the benefits/limitations of the approach. Based on Monte Carlo simulations, we present a survey of heterostructure performance versus detector design. The data allow for a clear understanding of the design/performance relationship. This, in turn, enables the establishment of design rules toward the development and optimization of heterostructured detectors that could supersede the current detector technology in the medical imaging field but also across multiple sectors (e.g. high-energy physics, security).

A processable, high-performance dielectric elastomer and multilayering process.

Dielectric elastomers (DEs) can act as deformable capacitors that generate mechanical work in response to an electric field. DEs are often based on commercial acrylic and silicone elastomers. Acrylics require prestretching to achieve high actuation strains and lack processing flexibility. Silicones allow for processability and rapid response but produce much lower strains. In this work, a processable, high-performance dielectric elastomer (PHDE) with a bimodal network structure is synthesized, and its electromechanical properties are tailored by adjusting cross-linkers and hydrogen bonding within the elastomer network. The PHDE exhibits a maximum areal strain of 190% and maintains strains higher than 110% at 2 hertz without prestretching. A dry stacking process with high efficiency, scalability, and yield enables multilayer actuators that maintain the high actuation performance of single-layer films.

A unimorph nanocomposite dielectric elastomer for large out-of-plane actuation.

Dielectric elastomer actuators (DEAs) feature large, reversible in-plane deformation, and stacked DEA layers are used to produce large strokes in the thickness dimension. We introduce an electrophoretic process to concentrate boron nitride nanosheet dispersion in a dielectric elastomer precursor solution onto a designated electrode surface. The resulting unimorph nanocomposite dielectric elastomer (UNDE) has a seamless bilayer structure with 13 times of modulus difference. The UNDE can be actuated to large bending curvatures, with enhanced breakdown field strength and durability as compared to conventional nanocomposite dielectric elastomer. Multiple UNDE units can be formed in a simple electrophoretic concentration process using patterned electrode areas. A disc-shaped actuator comprising six UNDE units outputs large bidirectional stroke up to 10 Hz. This actuator is used to demonstrate a high-speed lens motor capable of varying the focal length of a two-lens system by 40 times.

Soft strain-insensitive bioelectronics featuring brittle materials.

Advancing electronics to interact with tissue necessitates meeting material constraints in electrochemical, electrical, and mechanical domains simultaneously. Clinical bioelectrodes with established electrochemical functionalities are rigid and mechanically mismatched with tissue. Whereas conductive materials with tissue-like softness and stretchability are demonstrated, when applied to electrochemically probe tissue, their performance is distorted by strain and corrosion. We devise a layered architectural composite design that couples strain-induced cracked films with a strain-isolated out-of-plane conductive pathway and in-plane nanowire networks to eliminate strain effects on device electrochemical performance. Accordingly, we developed a library of stretchable, highly conductive, and strain-insensitive bioelectrodes featuring clinically established brittle interfacial materials (iridium-oxide, gold, platinum, and carbon). We paired these bioelectrodes with different electrochemical probing methods (amperometry, voltammetry, and potentiometry) and demonstrated strain-insensitive sensing of multiple biomarkers and in vivo neuromodulation.