Jamming of Miscible Liquids via Electrostatic Repulsion Between Polystyrene-Modified Gold Nanorods and Toluene.

Structured liquids in miscible fluids, due to ineffective resistance to withstand particle self-diffusion, differ from that in immiscible liquids because of interfacial interactions. Here, a kind of structured liquid, jammed by thiol-terminated polystyrene-modified gold nanorods (GNRs) within tetrahydrofuran and toluene (TOL), is developed by introducing electrostatic repulsion to counterbalance the self-diffusion of GNRs. First-principle calculations reveal charge transfer between the GNRs and TOL, resulting in the electrostatic repulsion. The structured liquids can be regarded as mimic "loading vehicles" to controllably carry and transport matter under electric or magnetic fields, where release rate can be adjusted by changing the concentration of the soluble matter for slow release and using the photothermal effect of the assembled GNRs for fast release. This work has developed a new assembly mechanism to form structured liquids, allowing the construction of a flexible and robust droplet platform with possible applications in microreactors, biomimetic permeable membranes, and functional liquid robots.

Nanostructured YbAgCu4 for potentially cryogenic thermoelectric cooling.

We have studied the thermoelectric properties of nanostructured YbAgCu4 materials. A high power factor of ∼131 µW cm(-1) K(-2) has been obtained at 22 K for nanostructured samples prepared by ball milling the arc melted ingot into nanopowder and hot pressing the nanopowder. The implementation of nanostructuring method decreased the thermal conductivity at 42 K by 30-50% through boundary scattering comparing with the previously reported value of polycrystalline YbAgCu4. A peak dimensionless thermoelectric figure-of-merit, ZT, of 0.11 has been achieved at 42 K, which may find potential applications for cryogenic cooling below 77 K. The nanostructuring approach can be extended to other heavy Fermion materials to achieve high power factor and low thermal conductivity and ultimately higher ZT.

Thermoelectric performance of Ni compensated cerium and neodymium double filled p-type skutterudites.

We have synthesized Ni compensated Ce and Nd double filled p-type skutterudites CexNdxFe3.7Ni0.3Sb12 with x = 0.35, 0.40, 0.45, and 0.5 by a melting-quenching-annealing method. The samples were made by directly hot pressing the hand ground powder at 650 °C for 5 minutes at a pressure of about 80 MPa. Since Ni has two more electrons than Fe, a lower power factor and a stronger bipolar effect in thermal conductivity are expected at higher temperature. In the experiments, we have demonstrated that by suitably tuning the Fe-Ni ratio and filler concentration, we can achieve both a higher power factor (∼35 µW cm(-1) K(-2) at 535 °C) and a lower thermal conductivity (∼2.1 W m(-1) K(-1) at room temperature and ∼2.7 W m(-1) K(-1) at 535 °C) in Ce0.4Nd0.4Fe3.7Ni0.3Sb12. A peak thermoelectric figure-of-merit of ∼1.1 at 475 °C is achieved in Ce0.4Nd0.4Fe3.7Ni0.3Sb12.

Controllable two-stage droplet evaporation method and its nanoparticle self-assembly mechanism.

Bottom-up self-assembly is able to constitute a variety of structures and has been thought to be a promising way for advanced nanofabrication. Droplet evaporation, as the simplest method, has been used in various self-assemblies. However, the assembled area is not large enough and the order is still not well controlled. Here we show a facile and controllable two-stage droplet evaporation method by adjusting the humidity and temperature of the evaporating droplet. Taking the highly monodispersed gold nanorods (GNRs) as an example, large-area, self-assembly monolayer arrays are reproducibly achieved. To understand the self-assembly mechanism, we adopted simplified models to analyze the interactions between the nanorods. The results show that a metastable state of secondary-energy-minimum exists, especially in the latter stage of the assembly process, leading to the ordered arrays. A large electrostatic barrier between the assembled arrays prevents the formation of the multilayer structures and thereby leads to the preferential monolayers. Moreover, we predict possibilities of different types of assemblies of the nanorods, and a schematic phase diagram is finally given. The results here may offer a way toward high-quality self-assembled nanoparticles superlattices for use in enhanced spectroscopy, sensors, or nanodevices.

Modified chemical vapor deposition synthesis of ultralong V2O5 nanobelt and its electronic properties.

The fascinating properties and wide applications of the V2O5 nanostructures have attracted significant attention over the past decades. In this paper, ultralong (centimeter-scale) single-crystal V2O5 nanobelts are successfully fabricated by modified chemical vapor deposition. The wide of the V2O5 nanobelts are 20-500 nm. The aspect ratio exceeds 10(5). The structure and crystal orientation of the nanobelts are investigated. X-ray diffractometer (XRD) patterns and Raman spectrum show the substrate temperature affecting the size and morphology of the V2O5 nanobelts. And the growth mechanism and electronic properties of the ultralong V2O5 nanobelt are studied in detail. The activation energy 0.12 eV is calculated. The fastest growth orientation along the [010] direction has been observed. Our work demonstrates that the single-crystal V2O5 nanobelt has potential applications in field-emitters, lithium-ion batteries, photodetectors, interconnect, and optoelectronic devices, etc.

A high quality BiOCl film with petal-like hierarchical structures and its visible-light photocatalytic property.

BiOCl film with petal-like hierarchical structures is obtained by dipping bismuth film into the mixed solution of H2O2 and HCl. To obtain a high quality BiOCI film, a connecting layer of Chromium is deposited between the substrate and Bismuth film. The product is easy-synthesized, high productive, reusable and environment-friendly. The structural analysis indicates that the BiOCI film is composed by petals with smooth surfaces, and the nanopetals grow along the (101) directions. Raman spectroscopy shows that the film has a good stress-resist feature. The PL spectrum shows that the defect energy levels of BiOCI nanostructure contribute to the excellent photoactivity of degradation the rhodamine B (RhB) under visible-light irradiation (A > 420 nm). This photocatalyst can keep stable photoactivity after it has been reused for 6 rounds. All those properties ensure the photocatalyst a bright future in the application of the pollution treatment.

Bioinspired Multimodal Multipose Hybrid Fingers for Wide-Range Force, Compliant, and Stable Grasping.

The increasing demand for grasping diverse objects in unstructured environments poses severe challenges to the existing soft/rigid robotic fingers due to the issues in balancing force, compliance, and stability, and hence has given birth to several hybrid designs. These hybrid designs utilize the advantages of rigid and soft structures and show better performance, but they are still suffering from narrow output force range, limited compliance, and rarely reported stability. Owing to its rigid-soft coupling structure with flexible switched multiple poses, human finger, as an excellent hybrid design, shows wide-range output force, excellent compliance, and stability. Inspired by human finger, we propose a hybrid finger with multiple modes and poses, coupled by a soft actuator (SA) and a rigid actuator (RA) in parallel. The multiple actuation modes formed by a pneumatic-based rigid-soft collaborative strategy can selectively enable the RA's high force and SA's softness, whereas the multiple poses derived from the specially designed underactuated RA skeleton can be flexibly switched with tasks, thus achieving high compliance. Such hybrid fingers also proved to be highly stable under external stimuli or gravity. Furthermore, we modularize and configure these fingers into a series of grippers with excellent grasping performance, for example, wide graspable object range (diverse from 0.1 g potato chips to 27 kg dumbbells for a 420 g two-finger gripper), high compliance (tolerate objects with 94% gripper span size and 4 cm offset), and high stability. Our study highlights the potential of fusing rigid-soft technologies for robot development, and potentially impacts future bionics and high-performance robot development.

Multimaterial Three-Dimensional Printing of Ultraviolet-Curable Ionic Conductive Elastomers with Diverse Polymers for Multifunctional Flexible Electronics.

Ionic conductive elastomers (ICEs) are emerging stretchable and ionic conductive materials that are solvent-free and thus demonstrate excellent thermal stability. Three-dimensional (3D) printing that creates complex 3D structures in free forms is considered as an ideal approach to manufacture sophisticated ICE-based devices. However, the current technologies constrain 3D printed ICE structures in a single material, which greatly limits functionality and performance of ICE-based devices and machines. Here, we report a digital light processing (DLP)-based multimaterial 3D printing capability to seemly integrate ultraviolet-curable ICE (UV-ICE) with nonconductive materials to create ionic flexible electronic devices in 3D forms with enhanced performance. This unique capability allows us to readily manufacture various 3D flexible electronic devices. To demonstrate this, we printed UV-ICE circuits into polymer substrates with different mechanical properties to create resistive strain and force sensors; we printed flexible capacitive sensors with high sensitivity (2 kPa-1) and a wide range of measured pressures (from 5 Pa to 550 kPa) by creating a complex microstructure in the dielectric layer; we even realized ionic conductor-activated four-dimensional (4D) printing by printing a UV-ICE circuit into a shape memory polymer substrate. The proposed approach paves a new efficient way to realize multifunctional flexible devices and machines by bonding ICEs with other polymers in 3D forms.

Ultrathin Hydrogel Films toward Breathable Skin-Integrated Electronics.

On-skin electronics that offer revolutionary capabilities in personalized diagnosis, therapeutics, and human-machine interfaces require seamless integration between the skin and electronics. A common question remains whether an ideal interface can be introduced to directly bridge thin-film electronics with the soft skin, allowing the skin to breathe freely and the skin-integrated electronics to function stably. Here, an ever-thinnest hydrogel is reported that is compliant to the glyphic lines and subtle minutiae on the skin without forming air gaps, produced by a facile cold-lamination method. The hydrogels exhibit high water-vapor permeability, allowing nearly unimpeded transepidermal water loss and free breathing of the skin underneath. Hydrogel-interfaced flexible (opto)electronics without causing skin irritation or accelerated device performance deterioration are demonstrated. The long-term applicability is recorded for over one week. With combined features of extreme mechanical compliance, high permeability, and biocompatibility, the ultrathin hydrogel interface promotes the general applicability of skin-integrated electronics.

Tailoring Poly(Styrene-co-maleic anhydride) Networks for All-Polymer Dielectrics Exhibiting Ultrahigh Energy Density and Charge-Discharge Efficiency at Elevated Temperatures.

Polymer film capacitors have been widely used in electronics and electrical power systems due to their advantages of high power densities, fast charge-discharge speed, and great stability. However, the exponential increase of electrical conduction with temperature and applied electric field substantially degrades the capacitive performance of dielectric polymers at elevated temperatures. Here, the first example of controlling the energy level of charge traps in all-organic crosslinked polymers by tailoring molecular structures that significantly inhibit high-field high-temperature conduction loss, which largely differs from current approaches based on the introduction of inorganic fillers, is reported. The polymer network with optimized crosslinking structures exhibits an ultrahigh discharged energy density of 7.02 J cm-3 with charge/discharge efficiencies of >90% at 150 °C, far outperforming current dielectric polymers and composites. The charge-trapping effects in different crosslinked structures, as the origins of the marked improvements in the high-temperature capacitive performance, are comprehensively investigated experimentally and confirmed computationally. Moreover, excellent cyclability and self-healing features are demonstrated in the polymer film capacitors. This work offers a promising pathway of molecular structure design to scalable high-energy-density polymer dielectrics capable of operating under harsh environments.

Wide-Humidity Range Applicable, Anti-Freezing, and Healable Zwitterionic Hydrogels for Ion-Leakage-Free Iontronic Sensors.

Hydrogels have entered the spotlight for applications in soft electronics. It is essential and challenging to obtain hydrogels that can function properly under varying environmental circumstances, that is, 30-90% relative humidity (RH) and -20 to 40 °C due to their intrinsic nature to lose and absorb water upon variations in humidity and temperature. In this work, a green solvent, solketal, is introduced into poly 3-dimethyl-2-(2-methylprop-2-enoyloxy)ethyl azaniumyl propane-1-sulfonate (poly(DMAPS)) zwitterionic hydrogels. Compared to glycerol, solketal endows hydrogels with greater possibility for further modification as well as improved water content and mechanical performance consistency over 30-90% RH. Encouragingly, the optimized hydrogel demonstrates its unique merits as a dielectric layer in iontronic sensors, featuring non-leaky ions, high sensitivity (1100 kPa-1 ), wide humidity, and temperature range applicability. A wide-humidity range healable and stretchable electrode is attained by combining the hydrogel substrate with Ag paste. A full-device healable and highly-sensitive sensor is developed. This study is a pioneering work that tackles the broad humidity range applicability issue of hydrogels, and demonstrates the ion-leakage-free ionic skins with zwitterionic dielectrics. The outcomes of the study will considerably promote advancements in the fields of hydrogel electronics and iontronic sensors.

Fast visible light photoelectric switch based on ultralong single crystalline V2O5 nanobelt.

A photoelectric switch with fast response to visible light (<200 µs), suitable photosensitivity and excellent repeatability is proposed based on the ultralong single crystalline V2O5 nanobelt, which are synthesized by chemical vapor deposition and its photoconductive mechanism can well be explained by small polaron hopping theory. Our results reveal that the switch has a great potential in next generation photodetectors and light-wave communications.

Micro-optical elements fabricated by metal-transparent-metallic-oxides grayscale photomasks.

One-step gray-tone lithography is the most effective approach to making three-dimensional (3D) micro-optical elements (MOEs). Metal-transparent-metallic-oxide (MTMO) grayscale masks are novel and quite cost effective. In this paper, through the successful fabrication of 3D SiO(2) MOEs by gray-tone lithography and reactive ion etching, we thoroughly investigate the practical technique needs of MTMO grayscale masks on metallic nanofilms. Design calibration, pattern transfer, resolution, lifetime, and mask protection of grayscale masks have been verified. This work shows that the MTMO grayscale photomask has good practical applicability in the laboratory and in industry.

Adhesion-Shielding based synthesis of interfacially active magnetic Janus nanoparticles.

HYPOTHESIS: A unique adhesion-shielding (AS)-based method could be used to manufacture magnetic Janus nanoparticles (IM-JNPs) of promising interfacial activities, asymmetric surface wettability, and great performance on deoiling from oily wastewater under the external magnetic field. EXPERIMENTS: The IM-JNPs were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). The interfacial properties of IM-JNPs were investigated by the measurements of interfacial pressure-area isotherms (π-A), oil-water interfacial tension, and the related crumpling ratio. The Langmuir-Blodgett (L-B) technique was used to determine the asymmetric surface wettability of the IM-JNPs. The performance and recyclability of IM-JNPs for treating oily wastewater were also investigated. FINDINGS: Using the proposed AS-based method, 17.9 g IM-JNPs were synthesized at a time and exhibited excellent interfacial properties, as indicated by decreasing oil-water interfacial tension from 38 to 27 mN/m. The crumpling behavior of the oil droplet further demonstrated the irreversible deposition of IM-JNPs at the oil droplet surfaces. The L-B technique and water contact angle measurement confirmed the asymmetric surface wettability of the IM-JNPs. The IM-JNPs were applied to successful removal of > 90% emulsified oil droplets from the household-produced oily wastewater under the external magnetic field while realizing facile recyclability and regeneration.

TiO2 micro-devices fabricated by laser direct writing.

Constructing micro/nanostructures based on TiO2 has attracted increasing attention due to the excellent properties of TiO2. In this study, we report a simple method to directly fabricate TiO2 micro-devices, including Fresnel lens, gear structures and suspended beams only by laser direct writing and selective-etching processing. This route shows great potential in fabricating TiO2 structures for micro-electro-mechanical systems, diffractive optical elements and bio-applications, owing to its maskless process, low cost, and flexible dry/wet alternative etching treatment.

Self-assembly of gold nanorods into symmetric superlattices directed by OH-terminated hexa(ethylene glycol) alkanethiol.

The self-assembly of anisotropic gold nanorods (GNRs) into ordered phases remains a challenge. Herein, we demonstrated the fabrication of symmetric circular- or semicircular-like self-assembled superlattices composed of multilayers of standing GNRs by fine-tuning the repulsive interactions among GNRs. The repulsive force is tailored from electrostatic interaction to steric force by replacing the surface coating of cetyltrimethylammonium bromide (CTAB) (ζ potential of 20-50 mV) with an OH-terminated hexa(ethylene glycol) alkanethiol (here termed as EG(6)OH, ζ potential of -10 mV). The assembly mechanism is discussed via theoretical analyses of the major interactions, and an effective balance between the repulsive steric and attractive depletion interactions is the main driving force for the self-assembly. The real-time observations of solution assembly (UV-vis-NIR absorption spectroscopy) supports the mechanism that we suggested. The superlattices obtained here not only enrich the categories of the self-assembled structures but more importantly deepen the insight of the self-assembly process and pave the way for various potential applications.

Leaf-Inspired Flexible Thermoelectric Generators with High Temperature Difference Utilization Ratio and Output Power in Ambient Air.

The inherently small temperature difference in air environment restricts the applications of thermoelectric generation in the field of Internet of Things and wearable electronics. Here, a leaf-inspired flexible thermoelectric generator (leaf-TEG) that makes maximum use of temperature difference by vertically aligning poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and constantan thin films is demonstrated. Analytical formulae of the performance scales, i.e., temperature difference utilization ratio (φth) and maximum output power (Pmax), are derived to optimize the leaf-TEG dimensions. In an air duct (substrate: 36 °C, air: 6 °C, air flowing: 1 m s-1), the 10-leaf-TEG shows a φth of 73% and Pmax of 0.38 µW per leaf. A proof-of-concept wearable 100-leaf-TEG (60 cm2) generates 11 µW on an arm at room temperature. Furthermore, the leaf-TEG is flexible and durable that is confirmed by bending and brushing over 1000 times. The proposed leaf-TEG is very appropriate for air convection scenarios with limited temperature differences.

Controllable fabrication of super-resolution nanocrater arrays by laser direct writing.

A super-resolution fabrication technique for highly-ordered nanocrater arrays is reported based on laser direct writing method. Nanocraters with diameters up to 40 nm, which is much smaller than the diffraction limit of laser system, are fabricated on titanium films using a 532 nm laser. The diameters of the craters are tunable from 350 nm to 40 nm, with a rigorous linear relationship versus the writing laser powers and an approximate linear relationship versus pulse widths. Laser ablation and oxidation are involved in formation mechanism and Gaussian distribution of laser energy density is proposed to play a key role of super-resolution structures.

A novel BiOCl film with flowerlike hierarchical structures and its optical properties.

A novel BiOCl film with flowerlike hierarchical structures has been fabricated for the first time by dipping Bi film in a mixed solution of H(2)O(2) and HCl. This method presents the advantages of a simple technique, template-free, uniform and controllable morphology, as well as easy mass production. Each flowerlike hierarchical structure is composed of several dozen ultra-thin single-crystal nanopetals which grow along the 110 directions in the tetragonal structure. The layered growth of nanopetals is related to the more marked anion polarization along the c axis and layered stacking of various atoms (Cl-Bi-O-Bi-Cl). The growth mechanism of the BiOCl hierarchical structure is preferred to be a nucleation-dissolution-recrystallization process. A Raman shift originating from laser-induced compressive stress is observed. Photoluminescence (PL) spectra of the BiOCl film show principal green emission, indicating potential applications in optoelectronic devices.

The shape evolution of gold seeds and gold@silver core-shell nanostructures.

We report the seed-dependent shape evolution of gold@silver (Au@Ag) core-shell nanostructures with various morphologies through using pre-existing Au nanocrystals as nuclei in a polyvinylpyrrolidone (PVP)-assisted polyol reduction process. Au nanocrystalline seeds with different shapes such as cube, truncated-octahedron, octahedron, twinned hexagon and triangle, five-twinned decahedron and nanorod are firstly synthesized by refluxing a 1,5-pentanediol solution containing Au precursors in the presence of PVP. The Au seeds obtained in this way then serve as the nuclei for further epitaxial growth of Ag shells by using Ag precursors via the same route. Scanning transmission electron microscope (STEM) characterization of the products obtained demonstrates that the morphological evolution of the Ag shells depends completely on the shapes of the Au seeds that are used. We have observed that the Au@Ag core-shell nanostructures formed with various regular shapes such as cube, bi-triangle, and nanorod with five-twinned cross section, are mostly surrounded by {100}-type Ag crystalline facets. Our findings provide new evidence and clear evolution routines from the Au cores with well-defined shapes to the corresponding Ag shells for the Au@Ag core-shell nanostructures by the family of the PVP-assisted polyol reduction methods.