Composite Ink Research Articles

Balloon‐Embedded Sensors Withstanding Extreme Multiaxial Stretching and Global Bending Mechanical Stress: Towards Environmental and Security Monitoring

Balloon‐embedded stretchable sensors, undergoing a simultaneous equal‐multiaxial stretching along global bending motion, have been characterized and tested towards environmental and security monitoring missions. Stress‐enduring inks are printed on the curvilinear surface of conventional rubber balloons and their resilience to extreme mechanical deformations, associated with repeated inflation and deflation cycles, is investigated. Unlike early studies of mechanical deformed electrochemical devices—performed with linear stretching or bending—the present balloon‐embedded sensors undergo simultaneous multidimensional strains without any alteration of its electrochemical properties. Careful attention is given to the elastomeric, electrical, and electrochemical properties of the new expandable composite inks for addressing the extreme demands of the inflated spherical dynamic balloon substrate. The influence of the balloon inflation and corresponding multiaxial mechanical stress upon the electrochemical behavior is modeled analytically. The electrochemical detection of relevant military and homemade explosives in liquid and vapor phases is used to demonstrate the functionality and potential of the new balloon sensor system to diverse environmental and defense missions. Negligible changes in the response to explosive compounds are observed following multiple repeated inflation and deflation cycles, involving over 400% increase of the balloon area.

Screen-Printing Fabrication and Characterization of Stretchable Electronics.

This article focuses on the fabrication and characterization of stretchable interconnects for wearable electronics applications. Interconnects were screen-printed with a stretchable silver-polymer composite ink on 50-μm thick thermoplastic polyurethane. The initial sheet resistances of the manufactured interconnects were an average of 36.2 mΩ/◽, and half the manufactured samples withstood single strains of up to 74%. The strain proportionality of resistance is discussed, and a regression model is introduced. Cycling strain increased resistance. However, the resistances here were almost fully reversible, and this recovery was time-dependent. Normalized resistances to 10%, 15%, and 20% cyclic strains stabilized at 1.3, 1.4, and 1.7. We also tested the validity of our model for radio-frequency applications through characterization of a stretchable radio-frequency identification tag.

Fabrication of an electro-thermal micro-gripper with elliptical cross-sections using silver-nickel composite ink

This paper proposes a rapid fabrication process for miniaturized electro-thermal grippers by using silver-nickel composite ink. Thick resistive structures are dispensed on a silicon wafer by a dispenser, and the parameters of the dispenser can be controlled for different thicknesses of hot and cold arms in a micro-gripper. The fabricated single layer structures are almost symmetric about a central plane of symmetry, thus largely suppressing the out-of-plane deflection. Due to cross-sectional area difference of the cold and hot arms, the micro-gripper can be driven by applying dc voltages. Electrical and mechanical behaviors of the micro-grippers are simulated and tested, and the simulation results are in accordance with the experiment results. The simulated maximum temperature is 155°C, and occurs at the hot arms with an input voltage of 1.54V. The measured displacement of the micro-gripper is observed to be 311μm for an applied current of 0.26A with maximum power dissipation of 0.4W. The fabricated micro-gripper can grip a small styrofoam ball with a diameter of 1.3mm between both tips.

Printed shape-shifting materials mimic biological structures

A hydrogel composite ink adopts different three-dimensional configurations depending on how the ink is patterned on a surface.

나노컴포지트 카본 잉크가 전착된 일회용 도파민 바이오센서

A new nano-composite carbon ink for the development of disposable dopamine (DA) biosensors based on screen-printed carbon electrodes (SPCEs) is introduced. The method developed uses SPCEs coupled with a tyrosinase modified nano-composite carbon ink. The ink was prepared by an “in-house” procedure with reduced graphene oxide (rGO), Pt nanoparticles (PtNP), and carbon materials such as carbon black and graphite. The rGO-PtNP carbon composite ink was used to print the working electrodes of the SPCEs and the reference counter electrodes were printed by using a commercial Ag/AgCl ink. After the construction of nano-composite SPCEs, tyrosinase was immobilized onto the working electrodes by using a biocompatible matrix, chitosan. The composite of nano-materials was characterized by X-ray photoelectron spectroscopy (XPS) and the performance characteristics of the sensors were evaluated by using voltammetric and amperometric techniques. The cyclic voltammetry results indicated that the sensors prepared with the rGO-PtNP-carbon composite ink revealed a significant improvement in electro-catalytic activity to DA compared with the results obtained from bare or only PtNP embedded carbon inks. Optimum experimental parameters such as pH and operating potential were evaluated and calibration curves for dopamine were constructed with the results obtained from a series of amperometric detections at -0.1 V vs. Ag/AgCl. The limit of detection was found to be 14 nM in a linear range of 10 nM to 100 μM of DA, and the sensor’s sensitivity was calculated to be 0.4 μAμM −1 cm −2 .

Graphene Oxide-Based Electrode Inks for 3D-Printed Lithium-Ion Batteries.

All-component 3D-printed lithium-ion batteries are fabricated by printing graphene-oxide-based composite inks and solid-state gel polymer electrolyte. An entirely 3D-printed full cell features a high electrode mass loading of 18 mg cm(-2) , which is normalized to the overall area of the battery. This all-component printing can be extended to the fabrication of multidimensional/multiscale complex-structures of more energy-storage devices.

Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores.

Graphene is an atomically thin, two-dimensional (2D) carbon material that offers a unique combination of low density, exceptional mechanical properties, thermal stability, large surface area, and excellent electrical conductivity. Recent progress has resulted in macro-assemblies of graphene, such as bulk graphene aerogels for a variety of applications. However, these three-dimensional (3D) graphenes exhibit physicochemical property attenuation compared to their 2D building blocks because of one-fold composition and tortuous, stochastic porous networks. These limitations can be offset by developing a graphene composite material with an engineered porous architecture. Here, we report the fabrication of 3D periodic graphene composite aerogel microlattices for supercapacitor applications, via a 3D printing technique known as direct-ink writing. The key factor in developing these novel aerogels is creating an extrudable graphene oxide-based composite ink and modifying the 3D printing method to accommodate aerogel processing. The 3D-printed graphene composite aerogel (3D-GCA) electrodes are lightweight, highly conductive, and exhibit excellent electrochemical properties. In particular, the supercapacitors using these 3D-GCA electrodes with thicknesses on the order of millimeters display exceptional capacitive retention (ca. 90% from 0.5 to 10 A·g(-1)) and power densities (>4 kW·kg(-1)) that equal or exceed those of reported devices made with electrodes 10-100 times thinner. This work provides an example of how 3D-printed materials, such as graphene aerogels, can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications.

Formulation and performance of functional sub-micro CL-20-based energetic polymer composite ink for direct-write assembly

Direct writing deposition of energetic materials has been an area of interest for fuzing applications, novel initiation/booster trains, and for studying small scale detonations.

Fabrication and Characteristics of Reduced Graphene Oxide Produced with Different Green Reductants.

There has been an upsurge of green reductants for the preparation of graphene materials taking consideration of human health and the environment in recent years. In this paper, reduced graphene oxides (RGOs) were prepared by chemical reduction of graphene oxide (GO) with three green reductants, L-ascorbic acid (L-AA), D-glucose (D-GLC) and tea polyphenol (TP), and comparatively characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectra, Raman spectra and electrical conductivity analysis. Results showed that all these three reductants were effective to remove oxygen-containing functional groups in GO and restore the electrical conductivity of the obtained RGO. The RGO sample with L-ascorbic acid as a reductant and reduced with the existence of ammonia had the highest electrical conductivity (9.8 S·cm-1) among all the obtained RGO samples. The mechanisms regarding to the reduction of GO and the dispersion of RGO in water were also proposed. It is the good dispersibility of reduced graphene oxide in water that will facilitate its further use in composite materials and conductive ink.

Direct Pen Writing of Adhesive Particle-Free Ultrahigh Silver Salt-Loaded Composite Ink for Stretchable Circuits.

In this article, we describe a writable particle-free ink for fast fabrication of highly conductive stretchable circuits. The composite ink mainly consists of soluble silver salt and adhesive rubber. Low toxic ketone was employed as the main solvent. Attributed to ultrahigh solubility of silver salt in short-chain ketone and salt-assisted dissolution of rubber, the ink can be prepared into particle-free transparent solution. As-prepared ink has a good chemical stability and can be directly filled into ballpoint pens and use to write on different substrates to form well adhesive silver salt-based composite written traces as needed. As a result of high silver salt loading, the trace can be converted into highly conductive silver nanoparticle-based composites after in situ reduction. Because of the introduction of adhesive elastomeric rubber, the as-formed conductive composite written trace can not only maintain good adhesion to various substrates but also show good conductivity under various deformations. The conductivity of written traces can be enhanced by repeated writing-reduction cycles. Different patterns can be fabricated by either direct handwriting or hand-copying. As proof-of-concept demonstrations, a typical handwriting heart-like circuit was fabricated to show its capability to work under different deformations, and a pressure-sensitive switch was also manufactured to present pressure-dependent change of resistance.

Copper (II) Fluoride Cathodes in High Energy Primary Lithium Cells

QinetiQ has evaluated the performance of copper (II) fluoride (CuF2) in high energy density primary lithium cells. With a high density of 4.2 g/cm3, a theoretical initial voltage of 3.5 V vs. Li and a capacity of 528 mAh/g CuF2 appears competitive to well-known manganese dioxide, MnO2 (3.0 V, 308 mAh/g) and carbon mono fluoride, CFx (3.0 V, 864 mAh/g) making it attractive for further evaluation as a lithium cell cathode material. The aim of this work was to compare practical cell performance, including energy density and heat generation, at equivalent discharge rate or the same current per gram of active material for CuF2 and CFx pouch cells of equivalent format and volume. Heat generation is inherent to the reaction between CFx and lithium metal. Transition metal fluoride systems are also expected to inherently generate heat. Direct observation of heat generated during a cell discharge has not been reported for metal fluoride based cathodes to date. Initial studies focussed upon capacity and rate performance using a PTFE binder in Swagelok cells, where 507 mAh/g (96% of theoretical capacity) over an average voltage of 2.47 V was achieved at C/140 rate dropping to 70% at C/20, as shown in Fig. 1. The two stages in voltage profile seem related to formation of CuF followed by reduction to Cu. The conversion reaction is slower for this stage resulting in the sloped voltage profile observed. Composite ink formulation studies were conducted and down selection of binders appropriate to CuF2 led to the scale up and testing of coated electrodes, initial “Swagelok cells” and then in a multilayer pouch cell of 5.5 Ah theoretical capacity; the first reported for this cathode material. A higher specific current of 43 mA/g was applied in order to better observe any thermal effects in both materials. At this relatively high current and rate C/11.5 the CuF2 cell delivered 38% of theoretical capacity and remained 5°C cooler than the CFx cell (8.3 Ah) discharged at the same specific current or C/20 to the point of 2.0 V after which significant increase in heat was observed down to the 1.7 V cut off value (Fig. 2). The concept of using a mixed conducting matrices system, MCM’s [1] was explored with interest in improving CuF2 cathode performance and reducing the active material costs. The MCM’s typically metal oxides or sulphides, act as both ionic and electronic conductors and have been claimed to exhibit performance advantages over using carbon based conductive matrices alone. Composites of CuF2 with molybdenum trioxide MoO3 and with MnO2 were compared to previous results of pure CuF2 in “Swagelok cells”. Both showed some evidence of a synergistic effect manifesting as changes in discharge voltage profile. Further work would include investigation of these systems at higher rates and evaluation of the heat generated by these mixed metal composite systems in multilayer cells.

Electromechanical properties of PZT/P(VDF-TrFE) composite ink printed on a flexible organic substrate

The fabrication and electromechanical properties of composite inks consisting of 30–70 vol.% of piezoceramic PZT powder and piezoelectric co-polymer P(VDF-TrFE) are presented. Samples were stencil-printed on a commercial PET film and printable silver ink was used for the electrodes thus allowing a maximum process temperature of 130 °C. The relative permittivity at 1 kHz varied between 33 and 69 depending on poling and composite composition. The highest remanent polarization, up to 4.8 μC/cm2, with 34 MV/m electric field and piezoelectric coefficient d31 up to 17 pm/V, was obtained with a 50 vol.% PZT loading level. The mechanical and electrical results indicate that the developed composite ink enables fully printable and flexible sensor applications with an increased level of integration.

Preparation of BaTiO<sub>3</sub>/PMMA Dielectric Films by Screen Printing

The high-k composite dielectric ink is prepared by dispersing the surface modified BaTiO3 in PMMA solution. The high quality BaTiO3-PMMA composite films are screen printed on ITO glasses. BaTiO3 nanoparticles are surface modified with a silane coupling agent (MPTMS) to improve their affinity for PMMA matrix. The dielectric constant, loss tangent, specific capacitance and transmittance of BaTiO3/PMMA nanocomposites are investigated as the function of volume fraction of BaTiO3. These composites, which possess both high dielectric constant and low dissipation factors and can be screen printed at ambient temperature and pressures, have very wide practical applications.

Direct Inkjet Printing of Dielectric Ceramic/Polymer Composite Thick Films

This article describes the preparation of composite thick films via inkjet printing in one process step. A novel ceramic/polymer ink is developed, suitable for the fabrication of homogeneous dielectric composite thick films. Therefore, a barium strontium titanate (BST) dispersion is prepared and combined with a highly loaded polymer solution afterwards. Ba0.6Sr0.4TiO3 is synthesized by a sol‐gel method and dispersed in butyl diglycol using a stirred media mill. A poly(methyl methacrylate) (PMMA) solution is prepared in butanone and mixed with the BST dispersion to obtain an ink with a 50:50 volume ratio of BST and PMMA. The ink characteristics and printability are investigated, in particular the drying behavior of the ink at different temperatures and the morphology of the composite thick films.The drying behavior of low viscosity particle suspensions is often influenced by the coffee stain effect. However, for the developed composite ink no coffee stain effect is observed and homogeneous composite thick films are achieved. Afterwards, all‐inkjet‐printed capacitors are fabricated, using the developed composite ink. Finally, the relative permittivity εr and loss tangent tan δ of the composite thick films are determined.

A Fully Inkjet-Printed Wireless and Chipless Sensor for CO2and Temperature Detection

A study on a low-cost wireless fully inkjet-printed chipless sensor on a flexible laminate with three different inks is presented. It is based on two split ring resonator 90° oriented between each other to allow for independent responses on two polarizations. A deposit of a polymer/single walled carbon nanotube composite ink is used to allow for the detection of CO 2 as well as temperature. In this paper, it is shown that the inkjet printing of a polymer-based coating on top of the sensing/reactive deposit can significantly reduce the sensitivity to CO 2 , whereas the temperature sensitivity stays at same. Simulations and experimental results verify the repeatability of this topology.

Inkjet‐Printed Metal‐Insulator‐Metal Capacitors for Tunable Microwave Applications

A Ba0.6Sr0.4TiO3–ZnO–B2O3 composite ink was prepared and used for the manufacturing of fully inkjet‐printed metal‐insulator‐metal varactors. The dielectric thick films were co‐fired with printed silver electrodes at 850°C and show a fine grained microstructure. The films have a relative permittivity of εr = 129 and a dielectric loss of tan δ = 0.043 at f = 3 GHz. Printed varactors with different dielectric film thickness were prepared. The characterization of the printed structures and 3D electromagnetic simulations of the layout reveal the strong influence of electrode inductance and fringing effects on the properties of the components. The printed varactors reach tunabilities between 14.4% and 16.4% by applying a tuning field of 5 V/μm. To demonstrate the capability of the inkjet printing process for the preparation of tunable microwave devices, a fully inkjet‐printed phase shifter was fabricated. It is based on seven pairs of the printed varactors and reaches a phase shift of 180° and a figure of merit of 19°/dB at 3.4 GHz.

Nano-organic silver composite conductive ink for flexible printed circuit

A nano-organic silver composite conductive ink has been developed orienting to the flexible electronics. The conductive ink printed on the flexible substrates turned into highly conductive silver metal after sintered at 250°C. Viscosity and surface tension of the conductive ink were 2·3 cps and 26–29 dyne cm−1 respectively. The ink remained stable without condensation or agglomeration during preservation. The resistivity of the conductive film, after annealing, was 11·7 μΩ cm, while the adhesion reached 5B. Transmission electron microscopy (TEM) and scanning electron microscope (SEM) were conducted to observe the morphology of the conductive ink before and after heat treatment, and to help deducing a probable mechanism of the reaction during the synthesis and sintering process. The preparation and characterisation of the composite conductive ink were comprehensively demonstrated in this paper.

Printable and foldable electrodes based on a carbon nanotube-polymer composite

Foldable components such as electrodes, transistors, and sensors are necessary to realize wearable electronics to be reliable use. In this paper, we propose a printable and foldable electrode using a composite ink of carbon nanotubes and polymer. Relative resistance change corresponding to the foldability by folding the electrode up to 1000 times is relatively small ∼9.9 and ∼1.7% for the folding directions of tensile and compressive stress in the electrodes, respectively. As a proof-of-concepts, a foldable calculator is demonstrated without malfunction. This electrode may lead to develop foldable electronics furthermore and can be applied to a wide range of applications. Printable, foldable carbon nanotube-based electrode and its application of a foldable calculator.

Development of MnO2 cathode inks for flexographically printed rechargeable zinc-based battery

A novel roll-to-roll flexographic printing process for rechargeable zinc-based battery manufacturing was presented in this paper. Based on the fundamental operating mechanism of flexography, key criteria for developing functional flexographic printing inks were established, including composite ink rheology (steady-state viscosity and yield stress), ink wettability as well as ink dispersing qualities. A variety of MnO2 cathode inks were developed and analyzed comprehensively based on these criteria. A novel type of aqueous cathode ink based on PSBR polymeric binder showed excellent flexographic printability as well as promising electrochemical performance.

Enhancement of Processability and Electrical Resistance by Use of Ag-Based Composite Inks Containing Ultrafine SAC305 Alloy Nanoparticles

We propose use of Ag/Sn-3.0 (wt.%) Ag-0.5 Cu (SAC305) composite ink to reduce sintering temperature, sintering time, and material costs. The SAC305 nanoparticle (NP) surfaces were not capped by any stabilizers, which are detrimental to the resistivity of the sintered tracks. Compared with commercial pure Ag ink, use of Ag/3.2 (vol.%) SAC305 composite ink containing ultrafine SAC305 NPs resulted in outstandingly enhanced processability, enabling faster sintering at low temperatures. The average sheet resistance of composite ink samples sintered for 25 min at 170°C was as low as 0.011 Ω/□, comparable with that of a pure Ag sample sintered for over 30 min at 220°C. The morphology and the differential scanning calorimetry curves enabled explanation of the changes in the sintering behavior and sheet resistance. The Ag/SAC305 clusters in the composite ink sintered at 170°C grew, on average, to ~201.1–226.1 nm as a result of faster local liquid-phase sintering, and most of the Ag particles were mutually linked, dramatically changing the microstructure.