Silver Flakes Research Articles

Effect of silver morphology on rheology and photopolymerization characteristics of Silver-Hydroxyapatite slurry for Vat Photopolymerization-based 3D printing process

The present work deals with the processing of HA-silver photocurable slurry to make composites using the Vat-photopolymerization process. Slurries with increasing amount of silver addition in the HA-Ag (0, 5, 10, 15%) slurry have been prepared using monomers with photo-initiators and printed successfully. Silver powder used in this study is in the form of flakes and spheres. A shear thinning behaviour of all the compositions of the slurries has been observed which is essential to fabricate defect-free parts. With increase in silver addition to 15 wt%, the viscosity decreased by around 60 % however curing depth was compromised. From SEM micrographs it was observed that HA with silver flakes showed better sintering with sintering density of 95% compared to only HA and HA with spherical silver samples.

Dispense Printing of Silver Flake Inks on Hydrophilic and Hydrophobic Surfaces

In printed electronics, achieving precise deposition of conductive materials on challenging substrates like Teflon is critical. This study delves into dispense printing, a technique that offers precision and versatility for creating electronic patterns. The deposition of high‐viscosity silver flake inks on both hydrophobic surfaces is investigated, such as Teflon, and hydrophilic ones, highlighting the significant interplay between ink viscosity and substrate wettability. This interaction is key to controlling ink spreading, drying behavior, and, ultimately, printing success. Research explores the relationships between critical parameters such as nozzle height, dispense pressure, and print speed, aiming to enhance the quality and functionality of printed electronics. The printing process is analyzed through its distinct phases: extrusion from the nozzle, spreading on the substrate, and line shrinking during drying. This methodological approach allows one to pinpoint how each parameter specifically influences the printing outcome, particularly on challenging substrates like Teflon. By advancing the understanding of these dynamics, the study offers valuable theoretical insights and practical advancements for fabricating high‐quality, flexible electronics across diverse substrates. The findings underscore dispense printing's potential to meet the growing demand for flexible electronics.

Grain Structure Engineering in Screen-Printed Silver Flake-Based Inks for High-Temperature Printed Electronics Applications.

We extensively studied serigraphic screen-printed commercial silver flake inks loaded with silicon inclusions in order to achieve pinning at the grain boundaries. Based on grain size measurements using electron backscattered diffraction (EBSD), commercial silver ink with silicon microparticle content of 5 wt.% shows significant grain growth retardation compared to pristine silver ink, which stabilizes electrical conductivity up to 700 °C via a Zener pinning mechanism. The modified silicon-loaded silver ink experiences a two-times increase in grain size when heated up to 700 °C, compared to a seven-times increase for pristine silver ink. In turn, this enables operation temperatures significantly higher than the conventional operational window of microparticle-based silver inks, which are usually limited to 400 °C. Using isothermal exposures of 10 min up to 4 h, this phenomenon is observed at temperatures ranging from 250 °C to 900 °C. The electrical conductivity stability, grain size evolution and oxide contents were studied up to 4 h. The activation energy of silver ink with silicon inclusions is 54% lower than for pristine silver ink due to the pining effect, which retards grain growth via the Zener mechanism. Most importantly, the electrical resistivity remains stable up to 700 °C, which is more than twice the operation limit for off-the-shelf screen-printable silver flake inks. Hence, we demonstrate that adding controlled amounts of silicon particles to silver inks for grain structure engineering can open new vistas of possibilities for screen-printed metallic inks.

Correlation Effect on Different Temperature-Humidity Range of Highly Thermal GNP/AG/ SA Conductive Ink

The study evaluates how the resistivity and properties of the material change in response to environmental factors such as temperature and humidity, and how these changes impact its performance in various applications. In order to develop a highly thermal graphene hybridization conductive ink, a new formulation of conductive ink was formulated using graphene nanoplatelet (GNP), silver flake (Ag), and silver acetate (SA) as conductive fillers mixed with organic solvents. The batch of chemicals was converted into a powder by undergoing sonication and stirring to create a powdery state. The powder was then treated with organic solvents, specifically 1-butanol and terpineol, and mixed using a thinky mixer to form a paste. The GNP/Ag/SA hybrid conductive ink paste was then printed on copper substrates using a mesh stencil and was cured at 250°C for 1 hour. Cyclic testing had been conducted using a cyclic bending test machine and a cyclic torsion test machine in a heat chamber with different temperature-humidity. The new formulation then was characterized base on the electrical and mechanical behaviour. After the torsion and bending tests, the GNP/Ag/SA hybrid conductive ink formulation reliability was evaluated. GNP/Ag/SA hybrid conductive ink room temperature baseline and GNP/Ag/SA hybrid conductive ink after given different temperature-humidity were compared in terms of electrical and mechanical properties. Both cyclic bending and torsion testing results showed an increasing value of resistance and resistivity with every progress of bending and torsion cycle, which displays a clear trend. The results indicate that the average resistance values at all sample points either stay constant or decrease with the increasing temperature. This observation suggests that the ink's electrical conductivity remains rather stable as the temperature increases. Thus, even with rising temperatures, the ink's electrical conductivity remains stable, indicating the ink's capacity to preserve its integrity and structural qualities within a defined temperature range. Future research should focus on improving the adhesion, stability and reliability of stretchable conductive inks under various temperature and humidity conditions.

Electrically conductive and antimicrobial Pluronic-based hydrogels

Electrically conductive hydrogels (ECHs) combine the electrical properties of conductive materials with the unique features of hydrogels. They are attractive for various biomedical applications due to their smart response to electrical fields. Owing to their distinctive properties, such as biocompatibility, thermosensitivity and self-assembling behaviour, Pluronics can be adopted for the generation of hydrogels for biomedical applications. Here, innovative self-assembling ECHs holding antimicrobial properties for biomedical applications are developed, providing a full characterization of their macroscopic and microscopic properties. The rheological, morphological, and structural properties of Pluronic F68 (PF68) in the presence of conductive poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS) are studied to optimize the synthesis of novel biocompatible and electrically conductive hydrogels. The addition of silver (Ag) flakes to the aqueous samples of PF68/PEDOT:PSS is used to further enhance the systems electrical conductivity and antimicrobial potency. Aqueous optimal samples with 45 wt% PF68 and different PEDOT:PSS/silver contents are investigated by means of experimental rheology and small-angle X-ray scattering (SAXS), to unveil the influence of both PEDOT:PSS and silver on the phase diagram, macroscopic flow properties, and morphology of the Pluronic-based systems.The presence of PEDOT:PSS and silver flakes endows Pluronic systems with high conductive properties, while preserving the same self-assembly features of PF68 in water. Moreover, the functionalisation with silver flakes confers antimicrobial properties to the ECHs, as demonstrated by growth inhibition of the multi-drug resistant bacterium Staphylococcus aureus.The use of PF68 in this work provides a novel route for the synthesis of innovative ECHs, whose functionalities such as self-assembling behaviour, biocompatibility, conductivity, and bioactivity may inspire future avenues in the biomedical field.

Self-Healing and Shear-Stiffening Electrodes for Wearable Biopotential Sensing and Gesture Recognition.

The achievement of flexible skin electrodes for dynamic monitoring of biopotential is one of the challenging issues in flexible electronics due to the interference of large acceleration and heavy sweat that influence the stability of skin-electrode interfaces. This work presents materials and techniques to achieve self-healing and shear-stiffening electrodes and an associated flexible system that can be used for multichannel biopotential measurement on the skin. The electrode that is based on a composite of silver (Ag) flakes, Ag nanowires, and polyborosiloxane offers an electrical conductivity of 9.71 × 104 S/m and a rheological characteristic that ensures stable and fully conformal contact with skin and easy removal under different shear rates. The electrode can maintain its conductivity even after being stretched by more than 60% and becomes self-healed after mechanical damage. The combination of the electrodes with a screen-printed multichannel flexible sensor allows stable monitoring of both static and dynamic electromyography signals, leading to the acquisition of high-quality multilead biopotential signals that can be readily extracted to yield gesture recognition results with over 97.42% accuracy. The conductive self-healing materials and flexible sensors may be utilized in various daily biopotential sensing applications, allowing highly stable dynamic measurement to facilitate artificial intelligence-enabled health condition diagnosis and human-computer interface.

Boron nitride nanosheets synergized with two‐dimensional micron silver sheets to enhance thermal conductivity and insulation of epoxy resin composites

AbstractWith the rapid progress of the advanced electronic device industry, precision electronic instruments are gradually developing towards miniaturization. In this case, epoxy resin gradually attracts people's attention, but its intrinsic thermal conductivity is not high, and the resulting heat dissipation problem limits the further application of epoxy resin in the field of electronic packaging. Therefore, how to enhance the thermal conductivity of epoxy resins has become an urgent problem in the field of electronic packaging. In this work, BNNS was successfully prepared by stripping h‐BN into a flaky two‐dimensional material, which was added to the epoxy resin as a filler to make the composite material. And on the basis of the above, two‐dimensional micron silver flakes (AgMS) with different mass fractions were added to the composites, and the AgMS/BNNS/EP composites were successfully prepared. When BNNS was 25 wt% and AgMS was 1 wt%, its out‐of‐plane thermal conductivity was enhanced from 0.17 W m−1 K−1 of pure epoxy resin to 0.43 W m−1 K−1. When BNNS was 20 wt% and AgMS was 1 wt%, the breakdown strength was enhanced from 105 kV/mm for pure epoxy to 130 kV/mm. This work provides a new strategy for synthesizing high‐thermal‐conductivity epoxy matrix composites.

(Invited) 3D Printing-Assisted Casting of Conducting Polymers for Bioelectronics

3D structured conducting polymers, known for their high conductivity, low impedance, and tunable form factor, are promising candidates for various bioelectronics applications. However, achieving a balance between structural complexity, electrical conductance, and processing generality has been challenging in these materials. In this talk, I will discuss our efforts to address this trade-off through 3D printing-assisted casting. Light-based 3D printing is used to create hollow molds, providing structural complexity and design freedom, whereas the casting nature imparts material versatility. The casting molds are made of superabsorbent polymers and printed in a partially hydrated state. Their dehydration provides significant enhancement in feature resolution and excellent thermal and mechanical properties, making them versatile for casting. After casting, over-hydration of the molds facilitate their energy-efficient removal. Using poly(3,4-ethylenedioxythiophene) (PEDOT) as a model system, complex architectures such as octet and truncated octahedron can be achieved. Compositing silver flakes with PEDOT through a thermal injection process leads to prints with conductivity over 6000 S/cm and high environmental stability. This method can potentially be applied to other hard-to-print soft materials and composites.

Integrating High-Performance Flexible Wires with Strain Sensors for Wearable Human Motion Detection.

Flexible electronics have revolutionized the field by overcoming the rigid limitations of traditional devices, offering superior flexibility and adaptability. Conductive ink performance is crucial, directly impacting the stability of flexible electronics. While metal filler-based inks exhibit excellent conductivity, they often lack mechanical stability. To address this challenge, we present a novel conductive ink utilizing a ternary composite filler system: liquid metal and two micron-sized silver morphologies (particles and flakes). We systematically investigated the influence of filler type, mass ratio, and sintering process parameters on the composite ink's conductivity and mechanical stability. Our results demonstrate that flexible wires fabricated with the liquid metal/micron silver particle/micron silver flake composite filler exhibit remarkable conductivity and exceptional bending stability. Interestingly, increasing the liquid metal content results in a trade-off, compromising conductivity while enhancing mechanical performance. After enduring 5000 bending cycles, the resistance change in wires formulated with a 4:1 mass ratio of micron silver particles to flakes is only half that of wires with a 1:1 ratio. This study further investigates the mechanism governing resistance variations during flexible wire bending. Additionally, we observed a positive correlation between sintering temperature and pressure with the conductivity of flexible wires. The significance of the sintering parameters on conductivity follows a descending order: sintering temperature, sintering pressure, and sintering time. Finally, we demonstrate the practical application of this technology by integrating the composite ink-based flexible wires with conductive polymer-based strain sensors. This combination successfully achieved the detection of human movements, including finger and wrist bending.

Optimizing Silver Paste Conductivity with Controlled Convection for Nanowrinkle Growth.

Conductive silver paste plays a crucial role as an interconnecting material between electrodes and circuits in electronic circuits and solar cells. The quality of the silver paste is greatly influenced by the preparation of the conductive-phase silver powder and the sintering process. This study investigated the impact of fluid dynamics on the preparation of silver powder. Combined with X-ray diffractometer characterization and molecular dynamics simulation, the formation mechanism of wrinkled silver powder was explained. The wrinkled silver powder replaced the traditional smooth spherical silver powder, and the point contact between the smooth silver powder turned into a line and surface contact. After mixing and sintering with the micrometer flake silver powder, the electrical conductivity and sintering morphology of the silver paste were improved. Compared with the silver content of conventional silver paste (≥75 wt %), the silver paste of (9.23 ± 0.68) × 10-6 Ω cm can be prepared by curing at 250 °C for 45 min when wrinkled powder/flake powder = 1:1 and silver paste content was only 66.7%. This research work provides a new idea for the morphology control of submicrometer silver powder, which has important applications in the field of low-temperature silver paste for new N-type batteries.

Preparation of Gradient Polyurethane and Its Performance for Flexible Sensors.

Flexible sensors are prone to the problems of slow recovery rate and large residual strain in practical use. In this paper, a polyurethane functional composite with a gradient change in elastic modulus is proposed as a flexible sensor to meet the recovery rate and residual strain without affecting the motion. Different hard and soft segment ratios are used to synthesize a gradient polyurethane structure. The conductive percolation threshold was obtained between 45 wt% and 50 wt% of flake silver powder. Both gradient polyurethane and gradient polyurethane composites demonstrated that gradient materials can increase the recovery rate and reduce residual strain. The gradient polyurethane composites had a tensile strength of 3.26 MPa, an elastic modulus of 2.58 MPa, an elongation at break of 245%, a sensitivity coefficient of 1.20 at 0-25% deformation, a sensitivity coefficient of 11.38 at 25-75% deformation, a rate of recovery of 1.95 s at a time, and a resistance to fatigue (over 1000 cycles at a fixed strain of 20% showed a stable electrical response). The sensing performance under different cyclic strain frequencies was also investigated. The process has practical applications in the field of wearable skin motion and health monitoring.

Effect of Torsional Load on Electrical and Mechanical Properties/Behaviour of Stretchable GNP-Ag Conductive Ink

Stretchable conductive inks (SCIs) have gained significant attention in recent years due to their potential applications in flexible and wearable electronics. Graphene nanoplatelet (GNP) hybridization conductive ink is a promising material for stretchable electronics due to its high electrical conductivity and excellent mechanical properties. However, the resistivity of GNP ink on flexible substrates can be affected by various factors, such as the torsion of the substrate. This paper aims to investigate the effect of torsional load in terms of the electrical and mechanical behaviour of hybridization conductive ink between GNP and Ag. The research was carried out on the formulation and performance of GNP hybrids using GNP and silver flakes (Ag). The GNP hybrid ink was printed on a copper substrate using a mesh stencil method and cured at 250 °C for an hour. The resistivity was evaluated at room temperature before and after the torsional tests in terms of electrical characteristics. The finding exposed that the resistivity values for each of the three samples of torsional tests significantly changed after 1000 cycles. Eventually, the resistance value at cycle 5000 rose due to the damaging impact of increasing the number of torsional cycles on the sample. In future work, it is recommended that the evaluation is made under temperature dependence and supported by SEM images.

Biodegradable polylactic acid emulsion ink based on carbon nanotubes and silver for printed pressure sensors

Investigating biodegradable and biocompatible materials for electronic applications can lead to tangible outcomes such as developing green-electronic devices and reducing the amount of e-waste. The proposed emulsion-based conducting ink formulation takes into consideration circular economy and green principles throughout the entire process, from the selection of materials to the production process. The ink is formulated using the biopolymer polylactic acid dissolved in a sustainable solvent mixed with water, along with conductive carbon nanotubes (CNTs) and silver flakes as fillers. Hybrid conductive fillers can lower the percolation threshold of the ink and the production costs, while maintaining excellent electrical properties. The coating formed after the deposition of the ink, undergoes isothermal treatment at different temperatures and durations to improve its adhesion and electrical properties. The coating’s performance was evaluated by creating an eight-finger interdigitated sensor using a Voltera PCB printer. The sensor demonstrates exceptional performance when exposed to various loading and unloading pressures within the 0.2–500.0 kPa range. The results show a consistent correlation between the change in electrical resistance and the stress caused by the applied load. The ink is biodegradable in marine environments, which helps avoiding its accumulation in the ecosystem over time.

Strong coupling between WS2 monolayer excitons and a hybrid plasmon polariton at room temperature

Abstract Light–matter interactions between plasmonic and excitonic modes have attracted considerable interest in recent years. A major challenge in achieving strong coupling is the identification of suitable metallic nanostructures that combine tight field confinement with sufficiently low losses. Here, we report on a room-temperature study on the interaction of tungsten disulfide (WS2) monolayer excitons with a hybrid plasmon polariton (HPP) mode supported by nanogroove grating structures milled into single-crystalline silver flakes. By engineering the depth of the nanogroove grating, we can change the character of the HPP mode from propagating surface plasmon polariton-like (SPP-like) to localized surface plasmon resonance-like (LSPR-like). Using reflection spectroscopy, we demonstrate strong coupling with a Rabi splitting of 68 meV between the WS2 monolayer excitons and the lower HPP branch for an optimized nanograting configuration with 60 nm deep nanogrooves. In contrast, only weak coupling between the constituents is observed for shallower and deeper nanogratings since either the field confinement provided by the HPP is not sufficient or the damping is too large. The possibility to balance the field confinement and losses render nanogroove grating structures an attractive platform for future applications.

Projection Stereolithography 3D Printing High-Conductive Hydrogel for Flexible Passive Wireless Sensing.

Hydrogel-based electronics have inherent similarities to biological tissues and hold potential for wearable applications. However, low conductivity, poor stretchability, nonpersonalizability, and uncontrollable dehydration during use limit their further development. In this study, projection stereolithography 3D printing high-conductive hydrogel for flexible passive wireless sensing is reported. The prepared photocurable silver-based hydrogel is rapidly planarized into antenna shapes on substrates using surface projection stereolithography. After partial dehydration, silver flakes within the circuits form sufficient conductive pathways to achieve high conductivity (387 S cm-1). By sealing the circuits to prevent further dehydration, the resistance remains stable when tensile strain is less than 100% for at least 30 days. Besides, the sealing materials provide versatile functionalities, such as stretchability and shape memory property. Customized flexible radio frequency identification tags are fabricated by integrating with commercial chips to complete the accurate recognition of eye movement, realizing passive wireless sensing.

Study on Preparation of High-Performance Flake Silver Powder by Liquid Phase Reduction

Flake silver powder was prepared by liquid phase reduction method with silver nitrate as silver source, ferrous sulfate heptahydrate as reducing agent, citric acid and gum acacia as surfactants. The effects of reducing agent dosage, citric acid dosage, gum acacia dosage, silver nitrate dosage and reaction temperature on the properties of silver powder were studied. The results show that when the dosage of silver nitrate is 0.08 mol·L−1, the molar ratio of silver nitrate to ferrous sulfate heptahydrate is 1:2, the oxidizing solution is added to the reducing solution at the rate of 100 ml·min−1, the citric acid is added to the oxidizing solution at 7.5% of the mass of silver nitrate, the gum acacia is added equally dispersed to the oxidizing solution and the reducing solution, the addition amount is 20% of the mass of silver nitrate and the reaction temperature is 30 °C, the silver powder obtained is flake with good dispersion and narrow particle size distribution.

Synthesis and Characteristic Valuation of a Thermoplastic Polyurethane Electrode Binder for In-Mold Coating.

A polyurethane series (PHEI-PU) was prepared via a one-shot bulk polymerization method using hexamethylene diisocyanate (HDI), polycarbonate diol (PCD), and isosorbide derivatives (ISBD) as chain extenders. The mechanical properties were evaluated using a universal testing machine (UTM), and the thermal properties were evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The PHEI-PU series exhibited excellent mechanical properties with an average tensile strength of 44.71 MPa and an elongation at break of 190%. To verify the applicability of different proportions of PU as an electrode binder, PU and Ag flakes were mixed (30/70 wt%) and coated on PCT substrates, the electrodes were evaluated by four-point probe before and after 50% elongation, and the dispersion was evaluated by scanning electron microscopy (SEM). The electrical resistance change rate of PHEI-PU series was less than 20%, and a coating layer with well-dispersed silver flakes was confirmed even after stretching. Therefore, it exhibited excellent physical properties, heat resistance, and electrical resistance change rate, confirming its applicability as an electrode binder for in-mold coating.

A Flexible and Electrically Conductive Liquid Metal Adhesive for Hybrid Electronic Integration

AbstractElectrical and mechanical integration approaches are essential for emerging hybrid electronics that must robustly bond rigid electrical components with flexible circuits and substrates. However, flexible polymeric substrates and circuits cannot withstand the high temperatures used in traditional electronic processing. This constraint requires new strategies to create flexible materials that simultaneously achieve high electrical conductivity, strong adhesion, and processibility at low temperature. Here, an electrically conductive adhesive is introduced that is flexible, electrically conductive (up to 3.25×105 S m−1) without sintering or high temperature post‐processing, and strongly adhesive to various materials common to flexible and stretchable circuits (fracture energy 350 <Gc < 700 J m−2). This is achieved through a multiphase soft composite consisting of an elastomeric and adhesive epoxy network with dispersed liquid metal droplets that are bridged by silver flakes, which form a flexible and conductive percolated network. These inks can be processed through masked deposition and direct ink writing at room temperature. This enables soft conductive wiring and robust integration of rigid components onto flexible substrates to create hybrid electronics for emerging applications in soft electronics, soft robotics, and multifunctional systems.

Recyclable epoxy resins with different silyl ether structures: structure–property relationships and applications in diverse functional composites

In this work, three liquid silyl ether-containing cycloaliphatic epoxides (CESI1, CESI2 and CESI3) with different numbers of pendent phenyl groups were synthesized and cured by methylhexahydrophthalic anhydride. The high glass transition temperatures of the cured epoxy resins range from 150 to 184 °C, which increase with the increasing number of pendent phenyl groups. However, the tensile strengths of the cured epoxy resins decrease as the number of pendent phenyl groups increase. Incorporating dynamic silyl ether bonds enables the cured epoxy resins to be reprocessable and degradable. It is demonstrated that the pendent phenyl groups have a significant impact on the dynamic behaviors and degradation rates of cured epoxy resins. The reprocessing efficiencies and degradation rates of the three epoxy resins monotonously decrease with increasing the number of pendent phenyl groups. Finally, the CESI1 resin with the lowest viscosity was used as the polymer matrix for carbon fiber reinforced composites, electromagnetic wave absorbing coatings and silver-filled conductive adhesives. Notably, non-destructive recovery of carbon fibers, ferromagnetic particles and silver flakes can be achieved through the degradation of the epoxy matrix.

Simple Method for Enhancing Performance of the Bacterial Cellulose-Based Triboelectric Nanogenerator by Adding Conductive Interlayer

Surface charge density is a key factor that greatly enhances the performance of a natural-based triboelectric nanogenerator (TENG), which is essential for future sustainable sensing and harvesting devices. This work introduced a conductive interlayer between a main frictional layer and electrode. This approach can suppress the charge recombination rate and improve the amount of charges produced during the triboelectrification process. Bacterial cellulose (BC) film was selected as a main frictional layer for the TENG. A conductive nanomaterial, i.e. silver flake, was incorporated into the BC film as an intermediate layer for enhancing TENG performance. As firstly reported, the maximum electrical outputs for the multi-layer BC structure could be found when using silver flake/BC composite (ratio 1:5) as an intermediate layer, which has 122 V and 8.2 µA of output voltage and current, respectively. This is higher than the output voltage and current of a single layer BC TENG by approximately 3 and 8 times, respectively. The maximum output power of ∼440 µW is achieved by connecting with a load resistor of ∼10 MΩ. This demonstrates an efficient strategy for designing a high performance energy harvester by adding an intermediate layer for the target of practical purposes in sustainable systems.