Printable Electronics Research Articles

Multi-stimulus response AIE fluorescent hydrogel for “Blind box” multistage secure information encryption

Aggregation-induced emission (AIE) hydrogels have been widely applied in the field of information security due to their tunable optical properties and aggregation-induced emission properties. The introduction of spiropyranoid organic fluorescent dyes with multi-stimulus response into AIE hydrogels will endow them more functions. However, the traditional 2D anti-counterfeiting has the problem that the hidden information is easy to be copied. Therefore, it is urgent to develop a new anti-counterfeiting strategy to improve the level of information security. In this study, we present for the first time a new strategy of combining multi-stimulus response AIE fluorescent hydrogels with shape memory polyurethane to apply them in the field of information security. The polymer skeleton of fluorescent hydrogel (PCHS hydrogel) is composed of polyvinyl alcohol (PVA) and carboxymethyl chitosan (CMCS) through hydrogen bonding. Four [4-(3, 5-dicarboxyphenyl)] tetraphenyl ethylene (H8ETTB) and 1- (2-hydroxyethyl) −3, 3-dimethylindolin-6 ’-nitrobenzo spiropyrone (SP) are chosen as the fluorescent fillers. PCHS hydrogel is printed onto shape memory polyurethanes (SMPU) by a flexible electronic printer. As a result, the hidden information printed on the SMPU needs to be decrypted at temperatures (80 ℃) and under ultraviolet irradiation(365 nm). Moreover, the hidden information can be destroyed by adding H+ or applying external force after heating to 80 ℃. This effectively improves the security of the information and prevents its disclosure. Interestingly, we can choose the destruction method to make the destruction of information more flexible. This strategy has great potential in the field of information encryption and anti-counterfeiting.

Liquid Metal-Based Elastomer Composite with Selective Switchable Adhesion to Solids.

Selective switchable adhesion has recently attracted much attention due to its wide applications in transfer printing, information transfer, and flexible electronics. However, selective adhesive materials often have a complex adhesion or preparation process, which limits their use. To overcome this problem, this study prepares a composite of liquid metal foam and polydimethylsiloxane (PDMS) with selective photocontrolled adhesion, which can directly adhere to solids at room temperature. Utilizing the photoinduced phase transition of liquid metals, solid adhesion can be regulated by changing the backing layer modulus of the adhesive layer. Since the phase transition process is gradually completed by heat transfer from the illuminated side to the backlight side that adheres to the solid, the melting area on the backlight side can be regulated by controlling the light time, which determines the adhesion regulation area. Therefore, the accuracy of the adhesion regulation can reach less than 0.9 mm without relying on the accuracy of the infrared light. Moreover, based on the selective switchable adhesion, the selective transfer of solids with different scales can be achieved at room temperature. The findings of this study may provide strategies for the simple preparation of selective adhesive materials and the improvement of control accuracy.

Concentration-Switchable Assembly of Carbon Dots for Circularly Polarized Luminescent Amplification in Chiral Logic Gates and Deep-Red Light-Emitting Diodes.

Stimuli-responsive circularly polarized luminescent (CPL) materials are expected to find widespread application in advanced information technologies, such as 3D displays, multilevel encryption, and chiral optical devices. Here, using R-/S-α-phenylethylamine and 3,4,9,10-perylenetetracarboxylic dianhydride as precursors, chiral carbon dots (Ch-CDs) exhibiting bright concentration-dependent luminescence are synthesized, demonstrating reversible responses in both their morphologies and emission spectra. By adjusting Ch-CD concentration, the switchable wavelength is extended over 180nm (539-720nm), with the maximum quantum efficiency reaching 100%. Meanwhile, upon increasing Ch-CD concentration, the emission wavelength red-shifts, while the chirality of the assembled nanoribbons is synchronously amplified, ultimately achieving CPL at 709nm and a maximum luminescence asymmetry factor of 2.18 × 10-2. These values represent the longest wavelength and the largest glum reported for CDs. Considering the remarkable optical properties of the synthesized Ch-CDs, multilevel chiral logic gates are designed, and their potential practical applications are demonstrated in multilevel anti-counterfeiting encryption, flexible electronic printing, and solid-state CPL. Furthermore, deep-red chiral electroluminescence light-emitting diodes (EL-LEDs) are prepared using these Ch-CDs, achieving an external quantum efficiency of 1.98%, which is the highest value reported to date for CDs in deep-red EL-LEDs, and the first report of chiral electronic devices based on CDs.

Electric field-assisted micro-scale direct ink writing for electronic textiles

High-performance Kevlar fabric is widely employed in protective clothing. A recent trend involves the fusion of flexible conducting materials with protective textiles to create multifunctional E-textiles with microscale circuits. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) stands out as one of the most promising conducting polymers for flexible electronic applications, owing to its remarkable electrical, chemical and mechanical properties. Until recently, the production of PEDOT:PSS material on Kevlar fabric predominantly relied on dip coating and drop coating methods, presenting significant challenges for achieving microscale customized applications. Direct ink writing (DIW) has gained popularity due to its ability to fabricate a wide range of materials with programmed patterns and three-dimensional architectures, making it increasingly attractive for electronic printing. However, the rough surface of textiles and the die-swelling phenomenon exhibited by DIW printable materials have posed challenges for microscale E-textile fabrication. In previous studies, it was discovered that an electric field could facilitate material deposition on rough surfaces. This work investigates the potential to print PEDOT:PSS-based material patterns on rough textiles with a microscale resolution. It not only validated the effectiveness of the electric-field-assisted direct ink writing when printing PEDOT:PSS-based conducting inks on Kevlar but also identifies significant factors for achieving the microscale printing resolution. Additionally, this work characterizes the resistivity of the printed micro-traces and circuits. This research opens up possibilities for further exploration in customizing microscale circuits on various textiles.

Multi-Span Tension Control for Printing Systems in Gravure Printed Electronic Equipment

Multi-Span Tension Control for Printing Systems in Gravure Printed Electronic Equipment

Conformal printed electronics on flexible substrates and inflatable catheters using lathe-based aerosol jet printing

With the growth of additive manufacturing (AM), there has been increasing demand for fabricating conformal electronics that directly integrate with larger components to enable unique functionality. However, fabrication of conformal electronics is challenging because devices must merge with host substrates regardless of curvilinearity, topography, or substrate material. In this work, we employ aerosol jet (AJ) printing, an AM method for jet printing electronics using ink-based materials, and a custom-made lathe mechanism for mounting flexible substrates and 3D objects on a rotating axis. Using this method of lathe-based AJ printing, conformal electronics are printed around the circumference of rotational bodies with 3D curvilinear surfaces through cylindrical-coordinate motion. We characterize the diverse capabilities of lathe AJ (LAJ) printing and demonstrate flexible conformal electronics including multilayer carbon nanotube transistors. Lastly, a graphene sensor is conformally printed on an inflated catheter balloon for temperature and inflation monitoring, thus highlighting the versatilities of LAJ printing.

Study on Multi-Span Tension Coupling Relationship of Gravure Printed Electronic Equipment

To improve the performance of the tension control system in gravure printed electronic equipment, it is necessary to study the tension system model of gravure-printing electronic equipment. This paper focuses on the coupling characteristics of multi-span tension systems. Firstly, based on the single-span tension model, the mathematical model of the printing tension subsystem is established and simplified into a general multi-span tension coupling model. Then, using the relationship between the inputs and outputs of the system, the coupling model is simulated using MATLAB/Simulink and verified through experiments on the gravure printed electronic platform. Finally, the coupling relationship and influence laws among multi-physical quantities of the system are analyzed. The research results show that changes in the input web tension of the multi-span system will affect the steady-state tension values of all subsequent spans. Moreover, the speed change in a roller in the multi-span system will not only affect the steady-state tension value of its own span, but also cause transient tension fluctuations in all subsequent spans. The findings of this paper provide an important theoretical basis for the research of the tension system in gravure printed electronic equipment, contributing to the enhancement of printed electronic product quality.

Adapting and extending multimodal (inter)action analysis to investigate synchronous multimodal online language teaching

Abstract Multimodal (inter)action analysis offers a powerful and robust methodology for the study of action and interaction between social actors, their environment, and the objects and tools within. Yet its implementation in the analysis of synchronous multimodal online data sets, e.g. (inter)actions via videoconferencing, is limited. Drawing on our research in understanding teacher-learner (inter)actions in instruction-giving fragments in synchronous multimodal online language lessons, we describe and illustrate the ways in which we adapted and extended some of the methodological and analytical tools. These include (1) the use of a grounded theory approach in delineating and identifying higher-level actions, (2) the embodiment and disembodiment of frozen actions, (3) electronic print mode, (4) semiotic lag, (5) semiotic (mis)alignment, (6) modal density (mis)alignment, and (7) how modal density can be achieved by brisk modal shifts in addition to through modal intensity and complexity. We conclude by a call for further educational research in online teaching platforms using the framework to have richer understandings of the (inter)actions between social actors with particular roles and identities (teachers-learners), their environment, and the objects and tools within, which bring their “own material properties, feel and techniques of use, affordances and limitations” (Chun, Dorothy, Richard Kern & Bryan Smith. 2016. Technology in language use, language teaching, and language learning. The Modern Language Journal 100. 64–80: 65).

Conductive graphene-based coagulated composites for electronic printing applications

Graphene is gaining significance in applications such as sensors, antennas, photonics and spintronics. In particular, it is suitable for printing components and circuits affording the properties of high conductivity alongside flexibility, elasticity and wearability. For this application, graphene is typically customised into a fluidic form—ink or paint. This paper reports a novel, economical, scalable methodology for synthesising electrically conductive graphene-based coagulated composite that could be utilised in the above-mentioned applications. Composites are prepared from graphene powder/ink and screen-printing ink (GP–SPI and GI–SPI, respectively) at different mass ratios, and the optimal composition is identified by brush coating on paper in the form of rectangular strips. As a proof of concept, at optimum mass ratios, the GP–SPI and GI–SPI composites exhibit electrical conductivities ranging 0.068–0.702 mS m−1 and 0.0303–0.1746 μS m−1, in order. The as-prepared conductive composites are then screen-printed onto a square with an area of 1 cm2 on ceramic, FR4, glass, paper, polyester and wood substrates. The coagulated GP–SPI and GI–SPI composites are compatible with all these substrates and yield a conductive coating, demonstrating their suitability in multifaceted applications. Furthermore, the method proposed herein eliminates the need for rare/precious expensive materials, state-of-the art equipment, highly skilled personnel and costs associated with the same, thereby broadening the avenues for low-cost, fluidic graphene-based functional composites.

Coordinating the pore size of paper substrates and aspect ratio of silver nanowires to improve printed electronics

The internet of things is advancing toward a world of ubiquitous electronic devices, composed in large part of low-cost printed electronics (PE) such as sensors. PE typically use plastic substrates, such as polyethylene terephthalate (PET), but these materials are not biodegradable. The proliferation of PE devices and their degradation to form micro- and nanoplastics pose significant environmental hazards. Paper is a promising substrate to replace PET for greener PE due to its recyclability, affordability, and compatibility with many printing processes. However, the porous cellulosic structure of paper can be an obstacle when trying to print active inks due to wicking of the ink into the paper pores, which disperses the functional ink and negatively impacts electronic performance. Filling the pores of paper with a polymer to planarize the surface is a commonly used remedy, although this approach can compromise recyclability. Here, we present an approach to manage the dispersion of silver nanowires, a widely used and printable 1D nanomaterial ink, in paper substrates. We deposit solutions of short (20–30 μms) and long (100–200 μms) silver nanowires onto various graded filter papers that differ in pore size and examine the trends in wicking distance, wicking speed, and electrical properties. We show that with careful selection of AgNW length and the pore size of the paper, it is possible to control the lateral spreading of the ink and minimize the concentration of the AgNWs needed to achieve a specific electrical performance.

3D printing and 3D-printed electronics: Applications and future trends in smart drug delivery devices.

Drug delivery devices which can control the release of drugs on demand allow for improved treatment to a patient. These smart drug delivery devices allow for the release of drugs to be turned on and off as needed, thereby increasing the control over the drug concentration within the patient. The addition of electronics to the smart drug delivery devices increases the functionality and applications of these devices. Through the use of 3D printing and 3D-printed electronics, the customizability and functions of such devices can also be greatly increased. With the development in such technologies, the applications of the devices will be improved. In this review paper, the application of 3D-printed electronics and 3D printing in smart drug delivery devices with electronics as well as the future trends of such applications are covered.

Nanomaterials used in Flexible Electronics: Recent Trends and Future Approaches

Abstract: The latest research in soft electronics reveals a substantial demand for devices that can fold, bend and stretch to suit the requirements of technological advances. Cellulose, silk, and elastomers are employed in making biodegradable, environmentally benign substrates that accommodate nanofibers, nanoparticles, nanotubes, graphene, and biomaterials in their nano-form. Flexible materials can hold circuits and sensors and can substitute conventional substrates. Transient electronics, e-skin, and biosensors are the most sought-after in medical technology, sensors, energy storage devices, and wearables. These stretchable materials lead the way for developing eco-friendly and sustainable technology to attain sustainable development goals. This research work discusses nano species imbibed in printable and flexible electronics. An analysis of the documents extracted from the Scopus database using VOSviewer and patents in the domain of flexible electronics are presented along with altmetrics.

Greener alternative screen printable ink formulation for the development of flexible reference electrodes

Greener alternatives for high demand materials is becoming increasingly necessary. Conductive screen printable ink formulations are vital components of sensors, e.g., for glucose monitoring in diabetics, and printable electronics. Here, the formulation of a reliable, low-cost, high-performance and greener alternative of an Ag/AgCl screen-printable ink formulation is reported. The ink formulation has a significantly lower silver nanoparticle loading, 25 %, is based on a nontoxic organic solvent and uses a biodegradable polymeric mixture of polyhydroxyether/polyether resin (ratio of 1:2). The cytotoxicity of the Carbon/Ag/AgCl Ref SPE was evaluated and compared to screen-printed electrodes based on a commercial ink formulation. The Carbon/Ag/AgCl Reference screen printed electrodes (Carbon/Ag/AgCl Ref SPE) demonstrated good reproducibility, high analytical performance (RSD% 2.45) and the reference potential is highly stable in the electrochemical detection of glucose using a commercial glucose meter.

Room temperature compressed air-stable conductive copper films for flexible electronics

The state-of-the-art technology of fabricating printed copper electronics is focussed largely on thermal sintering restricting transition towards heat sensitive flexible substrates. Herein we report a pioneering technology which eliminates the need for conventional sintering. Biopolymer-stabilised copper particles are prepared such that they can be compressed at room temperature to generate air-stable films with very low resistivities (2.05 – 2.33 × 10−8 Ω m at 20 °C). A linear positive correlation of resistivity with temperature verifies excellent metallic character and electron microscopy confirms the formation of films with low porosity (< 4.6%). An aqueous ink formulation is used to fabricate conductive patterns on filter paper, first using a fountain/dip pen and then printing to deposit more defined patterns (R < 2 Ω). The remarkable conductivity and stability of the films, coupled with the sustainability of the approach could precipitate a paradigm-shift in the use of copper inks for printable electronics.

Flexible Resistive Gas Sensor Based on Molybdenum Disulfide-Modified Polypyrrole for Trace NO2 Detection.

High sensitivity and selectivity and short response and recovery times are important for practical conductive polymer gas sensors. However, poor stability, poor selectivity, and long response times significantly limit the applicability of single-phase conducting polymers, such as polypyrrole (PPy). In this study, PPy/MoS2 composite films were prepared via chemical polymerization and mechanical blending, and flexible thin-film resistive NO2 sensors consisting of copper heating, fluorene polyester insulating, and PPy/MoS2 sensing layers with a silver fork finger electrode were fabricated on a flexible polyimide substrate using a flexible electronic printer. The PPy/MoS2 composite films were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, and field-emission scanning electron microscopy. A home-built gas sensing test platform was built to determine the resistance changes in the composite thin-film sensor with temperature and gas concentration. The PPy/MoS2 sensor exhibited better sensitivity, selectivity, and stability than a pure PPy sensor. Its response to 50 ppm NO2 was 38% at 150 °C, i.e., 26% higher than that of the pure PPy sensor, and its selectivity and stability were also higher. The greater sensitivity was attributed to p-n heterojunction formation after MoS2 doping and more gas adsorption sites. Thus, PPy/MoS2 composite film sensors have good application prospects.

MXene Inks for High‐Throughput Printing of Electronics

AbstractMXene inks are promising alternatives for conventional conductive inks in printing electronics. However, the formulation of MXene inks is challenging due to the physicochemical properties of the few solvents in which MXenes can be dispersed. Furthermore, conventional MXene dispersions form high‐viscosity gels at low concentrations, making their ink formulation even more difficult. Here, a novel co‐solvent‐based approach is reported for dispersing MXenes in polar organic solvents that have excellent physicochemical properties as a carrier solvent for ink formulation but are not suitable for dispersing MXenes. Water is used as a dispersing agent and the second component of the co‐solvent system. The surfactant‐like role of water in dispersing MXenes in such solvents is also confirmed using molecular dynamics simulations. Using this strategy, the sol‐gel transition is significantly upshifted, enabling the formulation of highly concentrated inks with single‐ or few‐layered large‐flake MXenes. Numerous types of electronic components such as interconnects, resistors, transparent flexible conductive electrodes, and micro‐supercapacitors are fabricated using high‐throughput coating and printing techniques such as gravure printing, showcasing the immense potential of MXene inks for room‐temperature printing of electronics.

Inkjet Printing Optimization: Toward Realization of High‐Resolution Printed Electronics

AbstractThe printed electronics (PEs) market has witnessed substantial growth, reaching a valuation of USD 10.47 billion in the previous year. Driven by its extensive use in a multitude of applications, this growth trend is expected to continue with a projected compound annual growth rate of 22.3% from 2022 to 2032. Compared to screen printing, the adoption of inkjet printing (IJP) technology to manufacture PEs has been limited to laboratory‐scale research only. The fact that IJP's inability to maintain consistent high‐resolution quality over large printing areas has made transitioning IJP for commercial production arduous. Most of the previous literatures have focused on holistic discussion on material design for IJP, but this review provides insight into key aspects in material processing up to printing optimization to realize high‐resolution PEs. This review also highlights the challenges in controlling the functional ink properties and their interaction with the substrate as well as printing parameters to deliver the desired quality of the droplets and final prints. Imminent application of IJP in PEs and future perspectives are also included in this review.

Enhancing interfacial bond strength between PEEK and inkjet-printed silver film through laser surface modification for additive manufacturing of electronics

Electronic 3D printing is a very promising technology, which is widely used in the manufacturing of conformal antennas, flexible electronics and sensors. Polyether ether ketone (PEEK) is one of the most popular substrate materials for electronic 3D printing due to its superior fatigue resistance, heat tolerance, chemical resistance, and mechanical properties. However, the deficient bond between the PEEK substrate and the conductive ink leads to the peeling and shedding of the conductive pattern. This paper investigated the enhancement of the bond strength between the PEEK substrate and the conductive layer through PEEK surface modification. A 355 nm ns solid-state laser was used to treat the PEEK surface with different values of laser scanning spacing (S) and spot overlap rate (R). The surface microstructure, surface roughness, wettability, and functional groups of the treated substrates have been measured. Then the nanoparticle silver ink was printed and cured on the treated substrate. After that, the bonding strength was measured using a pull-off adhesion tester. Results showed that regular grooves were generated and the content of active oxygen atoms was increased on the PEEK surface through laser modification. The mechanical interlocking between the grooves and silver particles and hydrogen bonds induced by the active oxygen atoms and the hydroxyl groups contribute to the enhancement of bond strength between PEEK and silver film. The bond strength for the laser treated PEEK reached the maximum of 1.9 MPa, which was 413.51% higher than that of the untreated PEEK. The laser modification can effectively enhance the interfacial bond strength for additive manufacturing of reliable electronics.

The Role of Interdigitated Electrodes in Printed and Flexible Electronics.

Flexible electronics, also referred to as printable electronics, represent an interesting technology for implementing electronic circuits via depositing electronic devices onto flexible substrates, boosting their possible applications. Among all flexible electronics, interdigitated electrodes (IDEs) are currently being used for different sensor applications since they offer significant benefits beyond their functionality as capacitors, like the generation of high output voltage, fewer fabrication steps, convenience of application of sensitive coatings, material imaging capability and a potential of spectroscopy measurements via electrical excitation frequency variation. This review examines the role of IDEs in printed and flexible electronics since they are progressively being incorporated into a myriad of applications, envisaging that the growth pattern will continue in the next generations of flexible circuits to come.

Image-based identification of optical quality and functional properties in inkjet-printed electronics using machine learning

AbstractWe propose a novel image-analysis based machine-learning approach to the fully-automated identification of the optical quality, of functional properties, and of manufacturing parameters in the field of 2D inkjet-printed test structures of conductive traces. To this end, a customizable modular concept to simultaneously identify or predict dissimilar properties of printed functional structures based on images is described and examined. An application domain of the concept in the printing production process is outlined. To examine performance, we develop a dataset of over 5000 test structures containing images and physical characteristics, which are manufactured using commercially available materials. Functional test structures are fabricated via a single-nozzle vector-based inkjet-printing system and thermally sintered. Physical characterization of electrical conductance, image capturing, and evaluation of the optical quality of the test structures is done by an automatic in-house built measurement station. Conceptionally, the design of a convolutional neural network is described to identify the optical quality and physical characteristics based only on acquired images. A mathematical apparatus that allows assessment of the identification accuracy is developed and described. The impact of printing resolution, of emerging defects in the geometry of printed structures, and of image quality and color space on the identification accuracy is analyzed. Quality groups related to the printing resolution that affect identification accuracy are determined. Supplementarily, we introduce not yet reported classification of processes related to the fabrication of printed functional structures, adopted from the process analytical technology.