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Abstract Most triblock copolymer-based physical hydrogels form three-dimensional networks through micellar packing, and formation of polymer loops represents a topological defect that diminishes hydrogel elasticity. This effect can be mitigated by maximizing the fraction of elastically effective bridges in the hydrogel network. Herein, we report hydrogels constructed by complexing oppositely charged multiblock copolymers designed with a sequence pattern that maximizes the entropic and enthalpic penalty of micellization. These copolymers self-assemble into branched and bridge-rich network units (netmers), instead of forming sparsely interlinked micelles. We find that the storage modulus of the netmer-based hydrogel is 11.5 times higher than that of the micelle-based hydrogel. Complementary coarse grained molecular dynamics simulations reveal that in the netmer-based hydrogels, the numbers of charge-complexed nodes and mechanically reinforcing bridges increase substantially relative to micelle-based hydrogels.

Abstract Copper (Cu) is widely used as an industrial electrode due to its high electrical conductivity, mechanical properties, and cost‐effectiveness. However, Cu is susceptible to corrosion, which degrades device performance over time. Although various methods (alloying, physical passivation, surface treatment, etc.) are introduced to address the corrosion issue, they can cause decreased conductivity or vertical insulation. Here, using the nitrogen‐doped amorphous carbon (a‐C:N) thin film is proposed as a substrate on which Cu is directly deposited. This simple method significantly inhibits corrosion of ultrathin Cu (

Abstract Deformable and miniaturized energy storage devices are essential for powering soft electronics. Herein, we fabricate deformable micro supercapacitors (MSCs) based on eutectic gallium-indium liquid metal (EGaIn) current collectors with integrated graphene. The well-define interdigitated electrode patterning with controlled gap is successfully realized by using the laser ablation because of a strong laser absorption of graphene and EGaIn. By judicious control of gap size between neighboring interdigitated electrodes and mass loading of graphene, we achieve a high areal capacitance (1336 µF cm−2) with reliable rate performance. In addition, owing to the intrinsic liquid characteristics of EGaIn current collector, the areal capacitance of fabricated MSC retains 90% of original value even after repetitive folding and 20% stretching up to 1000 cycles. Finally, we successfully integrate deformable MSC with a commercial light-emitting diode to demonstrate the feasibility of MSC as a deformable power source. The fabricated MSCs operate stably under various mechanical deformations, including stretching, folding, twisting, and wrinkling.

Abstract Display form factors such as size and shape have been conventionally determined in consideration of usability and portability. The recent trends requiring wearability and convergence of various smart devices demand innovations in display form factors to realize deformability and large screens. Expandable displays that are foldable, multi-foldable, slidable, or rollable have been commercialized or on the edge of product launches. Beyond such two-dimensional (2D) expansion of displays, efforts have been made to develop three dimensional (3D) free-form displays that can be stretched and crumpled for use in realistic tactile sensation, artificial skin for robots, and on-skin or implantable displays. This review article analyzes the current state of the 2D and 3D deformable displays and discusses the technological challenges to be achieved for industrial commercialization.

Abstract Piezoelectric self‐powered sensors are promising platforms for wearable portable devices. Poly(vinylidene fluoride) (PVDF) and its copolymer derivatives are extensively explored as a soft piezoelectric material owing to their high piezoelectric coefficient, chemical thermal stability, biocompatibility, lightweight, and excellent flexibility. It is proved that the dominance of the electroactive (EA) β‐phase crystals versus the non‐electroactive α‐phase crystals is one of the key parameters to obtaining high piezoelectric performance of PVDF. Conventional methods, such as mechanical stretching, electrical poling, and high‐temperature annealing, are investigated to enhance the fraction of the β‐phase. Recently, embedding nanoscale fillers in the PVDF matrix has been investigated to further increase the β‐phase fraction and achieved considerable advances. The introduction of nanofillers is also advantageous in terms of improving the electrical conductivity and dielectric properties of PVDF, which are not readily obtained through conventional methods. This review introduces the principles of EA phase transformation in the presence of nanofillers and summarizes recent advances achieved by introducing various fillers, such as perovskites, oxide semiconductors, and 2D chalcogenides. The potential sensor applications of the PVDF nanocomposites responding to temperature, light, acoustic, and mechanical stimuli are reviewed. This review ends with the outlook of this new approach.

Abstract Although ion gels are attractive sensing materials for deformable epidermal sensors or implantable devices, their sensing performances are highly affected by environmental humidity change, so that their sensing reliability cannot be secured. This study proposes a new concept of maintaining the high‐precision temperature sensing performance of highly deformable ion gel sensors. In this approach, a hydrophobic ion gel sensing layer is kept water‐saturated by attaching a hydrogel layer, rather than attempting to completely block water penetration. This study performs experimental and theoretical investigation on water concentration in the ion gel, using the analysis of mass transportation at the interface of the ion gel and the hydrogel. By using the charge relaxation time of the ionic molecules, the temperature sensor is not affected by environmental humidity in the extreme range of humidity (30%–100%). This study demonstrates a highly deformable on‐skin temperature sensor which shows the same performance either in water or dry state and while exercising with large strains (ε = 50%).

Abstract Stretchable electronics has emerged over the past decade and is now expected to bring form factor‐free innovation in the next‐generation electronic devices. Stretchable devices have evolved with the synthesis of new soft materials and new device architectures that require significant deformability while maintaining the high device performance of the conventional rigid devices. As the mismatch in the mechanical stiffness between materials, layers, and device units is the major challenge for stretchable electronics, interface control in varying scales determines the device characteristics and the level of stretchability. This article reviews the recent advances in interface control for stretchable electronic devices. It summarizes the design principles and covers the representative approaches for solving the technological issues related to interfaces at different scales: i) nano‐ and microscale interfaces between materials, ii) mesoscale interfaces between layers or microstructures, and iii) macroscale interfaces between unit devices, substrates, or electrical connections. The last section discusses the current issues and future challenges of the interfaces for stretchable devices.

Ultrasound and optical imagers are used widely in a variety of biological and medical applications. In particular, multimodal implementations combining light and sound have been actively investigated to improve imaging quality. However, the integration of optical sensors with opaque ultrasound transducers suffers from low signal-to-noise ratios, high complexity, and bulky form factors, significantly limiting its applications. Here, we demonstrate a quadruple fusion imaging system using a spherically focused transparent ultrasound transducer that enables seamless integration of ultrasound imaging with photoacoustic imaging, optical coherence tomography, and fluorescence imaging. As a first application, we comprehensively monitored multiparametric responses to chemical and suture injuries in rats' eyes in vivo, such as corneal neovascularization, structural changes, cataracts, and inflammation. As a second application, we successfully performed multimodal imaging of tumors in vivo, visualizing melanomas without using labels and visualizing 4T1 mammary carcinomas using PEGylated gold nanorods. We strongly believe that the seamlessly integrated multimodal system can be used not only in ophthalmology and oncology but also in other healthcare applications with broad impact and interest. [ABSTRACT FROM AUTHOR]

Thin films of mixtures of asymmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) diblock copolymers and PMMA homopolymers with cylindrical PMMA microdomains oriented normal to the substrate surface are used to couple optical modes in the Kretschmann configuration, and their optical properties are investigated by optical waveguide spectroscopy. The sequential swelling/reannealing of the initial mixture film results in a number of discrete or partially interconnected pores.

The present study suggests a novel method to produce raspberry-like microparticles containing diverse functional materials inside. The raspberry-like microparticles were produced from a random assembly of uniformly-sized poly(methyl methacrylate) (PMMA) nanoparticles via electrospraying. The solution containing the PMMA nanoparticles were supplied through the inner nozzle and compressed air was emitted through the outer nozzle. The air supply helped fast evaporation of acetone, so it enabled copious amount of microparticles as dry powder. The microparticles were highly porous both on the surface and interiors, hence various materials with a function of UV-blocking (TiO2 nanoparticles and methoxyphenyl triazine) or antiaging (ethyl(4-(2,3-dihydro-1H-indene-5-carboxyamido) benzoate)) were loaded in large amount (17 wt % versus PMMA). The surface and interior structures of the microparticles were dependent on the characteristics of functional materials. The results clearly suggest that the process to prepare the raspberry-like microparticles can be an excellent approach to generate functional microstructures. [ABSTRACT FROM AUTHOR]

Foldable polymer thin film transistors gated by an ion gel dielectric were fabricated on a polymer substrate. Side gate structure was employed to simplify the fabrication process, which is a unique advantage of the transistors based on the ion gel dielectric. Utilizing the diffusion of crosslinkable oligomers in the P3HT thin films followed by UV gelation through a patterned mask, the ion gel made a strong bonding to the P3HT layer. Due to the deformable nature of the ion gel dielectric, the transistor arrays were electrically and mechanically stable at repeated folding events. [ABSTRACT FROM AUTHOR]

A spontaneous assembly route to form a thin film of nanowires (NWs) was demonstrated and its feasibility was confirmed through the fabrication of a high-performance multi-Si NW field effect transistor (FET) using this route. Governed by the three mechanisms of spreading, trapping, and two-dimensional packing, the route was optimized for the concentration of Si NWs and the initial volume ratio of aqueous hydrochloride solution to isopropyl alcohol. The successfully formed Si NW thin-film was transferred on a flat polydimethylsiloxane (PDMS) mold and regulated using a repeatable conformal contact method with a new flat PDMS to prepare it for decal printing on an organic dielectric layer. Finally, after depositing the source and drain electrodes on the printed active layer, a high-performance 23-bridged Si NW FET exhibiting a μeffof 51.4 cm2V−1s−1, an on/off drain current ratio of 105, and a Vthof −2.7 V was obtained. [ABSTRACT FROM AUTHOR]

Uniform regio-regular poly(3-hexylthiophene) nanofibers and their blend nanofibers with poly(-caprolactone) have been obtained by electrospinning and their electrical properties in single nanofiber field effect transistors have been compared. The key to the success was restricting the precipitation of P3HT at the nozzle tip, therefore preventing the nozzle from being clogged. The field effect mobility of pure P3HT fibers was 0.017 cm2V−1s−1which is acceptable for device fabrication. Blend fibers with PCL also showed field effect behaviour with slightly degraded electrical properties by an order or two. [ABSTRACT FROM AUTHOR]

Physical separation of Ag2Se colloids and trigonal (t) Se nanowires transformed from amorphous (a) Se@Ag2Se core−shell spherical colloids and from t-Se@Ag2Se core−shell nanowires was conducted above the softening temperature (∼132 °C) of Ag2Se. The Ag2Se shells in a-Se@Ag2Se core−shell colloids were first collapsed and then transformed into isolated solid spheres as the a-Se cores were dissolved in solvent and transformed into separate t-Se nanowires. In t-Se@Ag2Se core−shell nanowires, the soft Ag2Se shells dewetted on the t-Se nanowires and transformed into small droplets. While the formation of the spherical Ag2Se was not affected by the presence of surfactants, the structure of t-Se was highly dependent on the chemical structure of the polymeric surfactants. [ABSTRACT FROM AUTHOR]

This paper describes the generation of Pt nanoparticles inside hollow silica colloids. Solvent etching of a-Se core in a-Se@Pt@silica double-shelled colloids transformed the thin Pt layer into a number of Pt nanoparticles, decorating the interior surface of hollow silica colloids. The release rate of a-Se was directly related to the formation of Pt nanoparticles. Fast dissolution of the core in solvents such as carbon disulfide (CS 2) and hydrazine (N 2H 4) produced Pt nanoparticles with diameters less than 15 nm, while slow release of a-Se in alcohols or in a mixture of CS 2and water did not make any change in the Pt thin layer. At elevated temperatures (65 °C) in alcohols, the nanoparticles were aggregated and rearranged into large nanoparticles. The nanoparticles obtained in these processes were characterized single crystallites with HR-TEM analysis and electron diffraction patterns. [ABSTRACT FROM AUTHOR]

Spherical polymeric core−shell microcapsules in uniform size were produced by electrospraying with a coaxial nozzle setup. Contrary to the usual coaxial setup, the inner nozzle was slightly bent to touch the inside wall of the outer nozzle. A polymer solution for the core was introduced through the outer nozzle, and the other solution for the shell was supplied through the inner nozzle. The setup greatly increased reproduction of the same results. As a proof of the concept, core−shell microcapsules consisting of a PS or PMMA core and a PCL shell (PSPCL, PMMAPCL) were produced. When the volumetric feed rate of the shell-forming PCL solution was higher than that of the core-forming PS or PMMA solution the core−shell structures in uniform size were readily obtained. In contrast, irregular morphologies were observed when the feed rate of the PCL solution was slower or equal to that of the PS or PMMA solution. The size of the colloid was dependent on the relative feed ratio between the polymer solutions as well as the magnitude of applied voltage. [ABSTRACT FROM AUTHOR]

Microscale fish bowls, hollow particles with engineered holes in their surfaces, were prepared using two different methods. In the first method, commercial latex beads suspended in water were swollen with a good solvent of the polymer, followed by freezing with liquid nitrogen and evaporation of the solvent below 0 °C. While one big hole was generated when the amount of solvent used for the swelling was relatively low, small holes could be produced in the outer surface of each bowl by increasing the degree of swelling. The porosity and pore structure show a similar dependence on the degree of swelling for both amorphous and semicrystalline polymers even though they are supposed to exhibit different phase behaviors during the freezing and solvent evaporation processes. In the second method, a polymer emulsion in water was prepared and then frozen with liquid nitrogen, followed by solvent evaporation below 0 °C. The porosity and pore structure could be controlled by adjusting the concentration of the polymer solution used to prepare the emulsion. As for encapsulation, the bowl-shaped particles could be transformed back into solid beads via thermal annealing at a temperature near the glass transition temperature of the polymer or by adding a good solvent of the polymer to the colloidal suspension. In a proof-of-concept experiment, microscale fish bowls were fabricated from poly(caprolactone), quickly loaded with a fluorescent dye, and sealed through thermal annealing. The encapsulated dye could then be slowly released in a phosphate buffered saline, suggesting their potential use as a new class of microscale capsules for drug delivery. [ABSTRACT FROM AUTHOR]

The thermodynamic shape and position of a polymer drop sandwiched between two polymer melt plates were predicted by simulating the change of the interfacial energy according to various shapes and position of the drop. The calculation results were in a precise coincidence with the experimental results exhibiting lens, spreading, and encapsulation. The simple formula and easy concept of the calculation can be useful to predict the morphology of immiscible ternary blends with the information of the interfacial tensions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2729–2738, 2007 [ABSTRACT FROM AUTHOR]

Colloidal particles with hollow interiors play important roles in microencapsulation—a process that has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments or chemical reagents; protection of biologically active species; and removal of pollutants. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates by means of calcination or chemical etching. This simple and straightforward approach works for a variety of materials that include polymers, ceramics, composites and metals. For polymers, methods such as emulsion polymerization, phase separation, crosslinking of micelles and self-assembly have also been demonstrated for generating hollow structures. However, diffusion through these closed shells with pores <10 nm is often a slow process. To solve this problem, macroporous capsules have been fabricated by organizing colloids around liquid droplets to form colloidosomes or by controlling the mixing of liquid droplets. Here we report the preparation of another class of macroporous capsules—polymer shells with controllable holes in their surfaces. After loading of functional materials, the holes can be closed by means of thermal annealing or solvent treatment. [ABSTRACT FROM AUTHOR]

In the last decade, extensive studies have been conducted to realize the functions of human skin based on stretchable electronics. An artificial skin, recognizing complex mechanical stimulation including pressure, strain and shear, and composed of transparent material, is an essential goal but has hardly been achieved. We fabricated a transparent integrated sensor system that can sense the strain direction and normal pressure of applied mechanical stimulation. Each sensor is composed of micropatterned Ag nanowire, forming a composite stretchable conductor with a block copolymer elastomer. The micropatterning and transfer process using thermoplastic elastomer facilitates the transparent conductor to show high transmittance with low sheet resistance at the same time. The designed transparent strain sensor responds linearly to strain, but does not respond to the orthogonal direction, which enables it to have strain-directionality. The applied mechanical signal, comprising normal force and directional strain, can be interpreted through the electrical signal observed from integrated sensors. [ABSTRACT FROM AUTHOR]

We present patterned Ag-nanowire (AgNW) networks for their application to transparent electrodes in flexible devices. Using capillary-force-based soft lithography (CFL), we formed 25- to 30-µm-wide line patterns of AgNWs on flexible polymer substrates. Organic light-emitting diodes (OLEDs) and transparent thin-film heaters (TFHs) were successfully fabricated on the patterned substrates, which verified the potential of AgNW patterns formed by CFL as interconnects in flexible devices. [ABSTRACT FROM AUTHOR]

This study investigated the surface energy-controlled transformation of amorphous Se (a-Se) colloids into trigonal Se (t-Se) crystals on solid substrates. Hydrophilic surfaces generated nanowires laterally grown along the surface of the substrates, while on hydrophobic surfaces the nanowires on the colloidal surface were randomly oriented. The ripening was considered to govern the growth of t-Se nanowires. The in-plane growth of the nanowires along the substrates made possible the creation of a chemically interconnected nanowire network because the nanowires made branches on meeting other a-Se colloids and formed chemical junctions on encountering other growing nanowires. [ABSTRACT FROM AUTHOR]

The article presents a cancer research report on stretchable anisotropic conductive film (S-ACF) for electrical interfacing in high-resolution stretchable circuits. Topics include direct interfacing of chips by using the adhesion of the thermoplastic matrix; and integrate light-emitting diodes on the patterned S-ACF and demonstrate stable light operation at large biaxial areal stretching.