Ag Flakes Research Articles

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.

Decreasing Electrical Resistivity of Ag Film by Low-Temperature Evaporation and Sintering through Azeotrope Application

In the temperature-sensitive components, such as perovskite solar cells, large-area electrical connections with high electrical conductivity are also required. To fulfill the requirements, low-temperature evaporation was realized by preparing binder-free pastes with Ag flakes and a solvent mixture, followed by sintering at 140 °C. The mixed solvent was based on viscous α-terpineol with the addition of an appropriate amount of dipropylene glycol methyl ether acetate or diethylene glycol diethyl ether to achieve an azeotrope composition, followed by the addition of a low-molecular-weight hydroxypropyl cellulose to increase the viscosity and thixotropy. During sintering at 140 °C in air for up to 30 min, the paste with 49.5 wt% α-terpineol, 49.5 wt% dipropylene glycol monomethyl ether acetate, and 1 wt% hydroxypropyl cellulose mixture exhibited an excellent electrical conductivity of 7.72 × 10−6 Ω·cm despite the implementation of low-temperature sintering. The excellent processability of the prepared Ag-based pastes at 140 °C demonstrated their potential for novel application areas.

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.

Ultrahigh Thermal Conductivity of Epoxy/Ag Flakes/MXene@Ag Composites Achieved by In Situ Sintering of Silver Nanoparticles.

The growing use of high-power and integrated electronic devices has created a need for thermal conductive adhesives (TCAs) with high thermal conductivity (TC) to manage heat dissipation at the interface. However, TCAs are often limited by contact thermal resistance at the interface between materials. In this study, we synthesized MXene@Ag composites through a direct in situ reduction process. The Ag nanoparticles (Ag NPs) generated by the reduction of the MXene interlayer and surface formed effective thermally conductive pathways with Ag flakes within an epoxy resin matrix. Various characterization analyses revealed that adding MXene@Ag composites at a concentration of 3 wt % resulted in a remarkable TC of 40.80 W/(m·K). This value is 8.77 times higher than that achieved with Ag flakes and 7.9 times higher than with MXene filler alone. The improved TC is attributed to the sintering of the in situ reduced Ag NPs during the curing process, which formed a connection between MXene (a highly conductive material) and the Ag flakes, thereby reducing contact thermal resistance. This reduction in contact thermal resistance significantly enhanced the TC of the thermal interface materials (TIMs). This study presents a novel approach for developing materials with exceptionally high TC, opening new possibilities for the design and fabrication of advanced thermal management systems.

High electrical conductivity and bending resistance of Ag NPs/Ag flakes composite silver paste are achieved by sintering Ag NPs

The investigation of conductive silver pastes and inks has witnessed extensive research within the domain of printed electronics in recent years, primarily owing to the exceptional electrical conductivity and steadfastness intrinsic to silver. This paper introduces an approach for the fabrication of stable, cost-effective, and low-resistance conductive silver paste tailored for flexible printed circuits. This method facilitates the solidification of the conductive silver paste into a highly conductive silver film at a curing temperature of 250 °C. In the process of preparing the conductive silver paste, Ag flakes is subject to modification through the incorporation of Ag NPs, which are subsequently sintered at a low temperature curing setting. The sintering of Ag NPs serves to establish connections between adjacent particles of Ag flakes within the paste, thereby enhancing the conductivity and flexibility of the resulting conductive printed silver film. When the ratio of Ag NPs to Ag flakes is maintained at 10:90, the volume resistivity of the Ag NPs-modified film registers at 2.7 × 10−5 Ω.cm. This demonstrates a substantial 53.45% reduction in the volume resistivity of the conductive printed silver film modified with Ag NPs, compared to its Ag NPs-absent counterpart. Post 200 cyclic bending tests, it becomes evident that the resistance change rate in the Ag NPs-modified conductive printed silver film is a mere 12.5%, whereas the Ag NPs-modified silver film lacking Ag NPs displays a resistance change rate of 21.5%. This discrepancy underscores the capacity of Ag NPs-modified Ag flakes to fortify the bending resistance of the conductive printed silver film. Comprehensive data analysis substantiates that the improvements in electrical conductivity and bending resistance can be attributed to the superior bridging facilitated by the sintering process on the surface of the Ag NPs-modified Ag flakes.

Interface regulation of micro-sized sintered Ag-10Al composite based on in-situ surface modification and enhanced microstructure stability in power electronic packaging

The increasing demand for high-power SiC semiconductors necessitate the development of a die attachment material that combines high-temperature resistance, reliability, and cost-effectiveness. In this study, a novel micro-sized composite, Ag-10Al paste, containing 10 wt% Al particles, was designed. A remarkable phenomenon, the ejection of ultrafine Ag nanoparticles from micron-sized Ag flakes, was observed for the first time. The phenomenon was utilized for the in-situ surface modification of Al. Subsequently, the microstructure and mechanical properties of the sintered Ag-10Al/direct bonded copper (DBC) joints were studied. Results indicated that the Ag-10Al composite exhibited superior microstructure stability compared to sintered Ag. The Ag/Al interface was systematically analyzed, revealing a unique Ag/nano Ag2O/Al2O3 amorphous/Al structure. This structure was formed through the Ag nanoparticle jetting effect of Ag flakes, achieving effective bonding between nano Ag2O and Al2O3 amorphous phases through mutual dissolution at the atomic level. Moreover, the sintered Ag-10Al joint demonstrated enhanced mechanical performance stability over the sintered Ag joint. After 1000 h aging at 300 ℃, the shear strength of the sintered Ag-10Al joint reached 34.1 MPa, meeting the requirements for power semiconductor packaging. In conclusion, the Ag-10Al composite paste was thoughtfully designed, excelling in both performance and cost-effectiveness.

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.

Printed sustainable elastomeric conductor for soft electronics

The widespread adoption of renewable and sustainable elastomers in stretchable electronics has been impeded by challenges in their fabrication and lacklustre performance. Here, we realize a printed sustainable stretchable conductor with superior electrical performance by synthesizing sustainable and recyclable vegetable oil polyurethane (VegPU) elastomeric binder and developing a solution sintering method for their composites with Ag flakes. The binder impedes the propagation of cracks through its porous network, while the solution sintering reaction reduces the resistance increment upon stretching, resulting in high stretchability (350%), superior conductivity (12833 S cm−1), and low hysteresis (0.333) after 100% cyclic stretching. The sustainable conductor was used to print durable and stretchable impedance sensors for non-obstructive detection of fruit maturity in food sensing technology. The combination of sustainable materials and strategies for realizing high-performance stretchable conductors provides a roadmap for the development of sustainable stretchable electronics.

Pressureless sinter-joining of micron-Ag flake pastes at 160 °C enabled by solvent and interface engineering

Pressureless sinter-joining of cost-effective micron-Ag flake pastes at temperatures below 200 °C poses significant challenges due to their poor surface activity and low tapped density. Herein, we propose a novel solvent and interface engineering approach to enhance the contact among adjacent micron-Ag flakes and between the flakes and substrates. The solvent-enhanced sintering process is proposed, and its effect on the resistivity and shear strength of sintered Ag patterns and joints is studied in detail. Results show that the solvents with high wetting abilities on the Ag flakes and substrates are instrumental in achieving low resistivity and high shear strength in the sintered Ag patterns and joints. In particular, when the solvents possess high surface tension, they generate strong capillary adhesion among Ag flakes and substrates. This reduces the gap between Ag flakes and substrates, thereby promoting bonding among the Ag flakes by minimizing the distance of atom diffusion. Finally, mixed solvents of 50 % α-Terpineol and 50 % dipropyleneglycol methyl ether acetate show a synergistic effect due to the balance between wettability and surface tension, which enables the sintered joints to achieve an exceptional shear strength of 27 MPa even at an ultralow temperature of 160 °C. This achievement represents the state-of-the-art pressureless sinter-joining of Ag pastes and holds promising potential for practical use in power electronic packaging applications.

The Effect of Ni Interlayer Formation Plating Bath on the Suppression of Oxidation of Ag-Coated Cu Flakes

To suppress Ag dewetting from around 200 oC in Ag-coated Cu (Cu@Ag) flakes, Ag and Ni-coated Cu (Cu@Ni@Ag) flakes were fabricated by successive Ni and Ag electroless plating. The Ni bath type was an important consideration to induce differences in the Ag dewetting and resultant Cu oxidation. An acid Ni bath contained succinic acid as a complexing agent and sodium hypophosphite as a reductant, and an alkaline Ni bath contained sodium citrate as a complexing agent and sodium hydroxide as a pH adjuster as well as sodium hypophosphite. A hydrazine-based Ni bath contained sodium citrate, sodium hydroxide, and hydrazine hydrate as a reductant. The acid Ni bath provided amorphous coatings with a P content of approximately 10 wt%. The Cu@Ni@Ag flakes started the Ag dewetting and Cu oxidation at 350 oC, together with the formation of the Ni3P phase. Meanwhile, the alkaline Ni bath created Ni-5 wt% P amorphous Ni coatings, which transformed into a crystalline phase after heating at 350 oC. The Ag shell was dewetted at 450 oC, which caused oxidation of the flakes. Finally, the hydrazine-based Ni bath formed crystalline coatings without P, which induced rapid mixing with the core Cu. The Ag shells on the mixed Cu-Ni alloy showed repressed dewetting behavior, and thus the dewetting and oxidation temperature was the highest, such as 500 oC. Enhancing the high oxidation resistance at approximately 300 oC will enable the use of Cu@Ni@Ag flakes as a low-cost filler material in conductive pastes, especially for long-time or high-temperature curing.

Flexible and Printable Composite Ink for Thermal Management of Soft Electronics

AbstractSince heat generation in electronic devices causes thermal failure, heat dissipation is of critical importance. Furthermore, deformable devices are subjected to mechanical stress, therefore, mechanically stable thermal management material should be considered. Herein, a strategy for printable, thermally conductive, and mechanically stable composite ink for thermal management is introduced. Based on the galvanic replacement between eutectic gallium indium (EGaIn) nanoparticles and silver (Ag) flakes, decoration of the EGaIn nanoparticles on Ag flakes is resulted from the difference in standard reduction potential between Ag, Ga, and In. The resultant alloy formation(Ag–Ga or Ag–In) serves as the thermal transport junction between Ag flakes, leading to high thermal and electrical conductivity (≈140 W mK−1 and ≈106 S m−1, respectively). In addition, owing to the polymer binder, the printed ink is mechanically stable on a substrate exhibiting stable thermal conductivity and sheet resistance under the cyclic bending test. Notably, the heat dissipation of the light‐emitting diode (LED) showed better performance when applied with the developed composite ink compared to commercial Ag paste and thermal paste. The junction temperature of the LED is reduced effectively, resulting in a longer lifetime of the LED. The thermal management solution can be utilized in next‐generation soft electronics.

Triboelectric Nanogenerators (TENGs) Based on Various Flexible Polymeric Materials Along With Printed and Non-Printed Electrodes

Four designs (D1-D4) of flexible triboelectric nanogenerators (TENGs) were successfully fabricated in three different configurations for energy harvesting applications. Typically, TENG consists of anode layer, cathode layer, and electrodes. Combination of materials were investigated in this study using polyethylene terephthalate (PET), thermoplastic polyurethane (TPU) and a flexible fabric as top triboelectric (cathode) layers; Kapton and polydimethylsiloxane (PDMS) as bottom triboelectric (anode) layers. Copper (Cu) tape and screen-printed silver (Ag) were used as electrodes. Each of these designs (D1-D4) has three configurations C1, C2 and C3 in which the top substrate (cathode layer) was different from one configuration to other. In order to determine the best material combination that would provide better TENG performance, different configurations were considered. The capability of the TENGs in terms of open circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) and short circuit current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ) were demonstrated by subjecting them to ~5 to 6 N force at 10 Hz operating frequency. A maximum V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> of 21.61 ± 2.27 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , 35.32 ± 0.89 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , 31.21 ± 1.43 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> and 45.75 ± 5.09 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> resulted in a power density of 0.29 μW/cm², 1.12 μW/cm², 0.47 μW/cm² and 0.91 μW/cm² from the D1, D2, D3 and D4 designs, respectively. The TENG fabricated using screen printed Ag flake on PDMS and fabric (D4) exhibited the highest open circuit output and a good repeatability after six months of re-testing with a maximum difference of ~ 7.39 % change(ΔV/V) in the output signal. In addition, a cyclic test was performed on D4, the results obtained demonstrate a good durability of the TENG sensor over 1000 cycles. The fabricated TENG device has a simple design, compact size, and demonstrated a better performance in comparison with some of the other works in terms of output voltage.

Dielectric properties of a linear polymer-matrix composite filled with aligned Ag@BaTiO3 flakes

Composites with linear dielectric properties possess advantages in energy storage fields for the high charge-discharge efficiency with low energy loss. However, energy density of them is limited due to low permittivity. Here, a linear dielectric polydimethylsiloxane (PDMS) composite filled with parallel aligned core-shell Ag@BaTiO3 (BT) 2D flakes is prepared by directional shearing, which possesses high permittivity and excellent energy storage properties. Compared with traditional polymer/core-shell hybrid filler composites, this work presents modified filler composition, different filler dimension and enhanced energy storage performances. Conformably-coated Ag@BT flakes are prepared through simultaneous hydrolysis on polyvinylpyrrolidone-functionalized Ag flakes, forming a smooth ∼100 nm thick coating layer. The aligned PDMS/40 vol% Ag@BT flake composite exhibits a very high permittivity of 347 and a low dielectric loss< 0.03 at 100 Hz from 20 to 150 °C. The comp°site exhibits an enhanced breakdown strength of 26 kV cm−1 owing to BT coverage-shell blocking and parallel filler arrangement, compared with that of percolative composites filled with metal particles without shell-coverage. The composite exhibits linear dielectric characteristics with high discharged energy density of 6.18 × 10−3 J cm−3 and superhigh charge-discharge efficiency> 95% at 20 kV cm−1. This study demonstrates Ag@BT flake based linear-polymer composites for energy related applications.

A Stretchable Conductor Based on Spray-Coated Micro/Nano Scale Ag Flakes with Ultralow Resistance for Wearable Antennas

With the rapid development of wireless communication, there are demands on the flexible antennas. In this work, a wearable dipole antenna has been fabricated by spray-coating nano/microscale Ag flakes onto the polyurethane (TPU) template. It demonstrates an ultrahigh electrical conductivity even under large deformation such as bending, twisting, folding and stretching to 170%. Thus, the resultant antenna maintains good properties under the aforementioned deformation. And even under a stretching of 50%, in contact with the body, it can still provide good antenna characteristics. We hope that our results can be adopted for adaptive skin contactable flexible antenna under different conditions, which is crucial for the next generation of wireless communication.

Surface treatment of micron silver flakes with coupling agents for high-performance electrically conductive adhesives

Coupling agents are widely used in order to improve the properties of electrically conductive adhesives (ECAs). The effects of different coupling agents on the characteristics of epoxy-based ECAs were investigated in terms of thermal, rheological, electrical and mechanical properties. Results showed that the ECAs had favourable flow, adhesion and good conductivity. In particular, the ECAs filled with Ag flakes treated with the silane coupling agent 3-aminpropyltriethoxysilane (KH-550) exhibited the lowest electrical resistivity (5.22 × 10−4 Ω cm) and the highest shear strength (20.32 MPa) among the ECAs. Besides, it had the minimum viscosity 154 Pa s at 5 rpm/25 °C. It was also found that the adding of coupling agents had different effects on the aging electrical and shear strength of the ECAs. According to this study, the use of KH-550 had a significant electrical conductivity improvement and shear strength increase before and after aging. In addition, a strong adhesion/bonding between the conductive fillers and the resin matrix was revealed by scanning electron microscopy studies.

Printable and Highly Stretchable Viscoelastic Conductors with Kinematically Reconstructed Conductive Pathways.

Printable and stretchable conductors based on metallic-filler-reinforced polymer composites that can maintain high electrical conductivity at large strains are essential for emerging applications in wearable electronics, soft robotics, and bio-integrated devices. Regulating microstructures of conductive fillers during mechanical deformations is the key to reconstructing the conductive pathway and retaining high electrical conductivity, which has proven to be challenging. Here, it is reported that Ag flakes can spontaneously reorganize inside a viscoelastic, liquid-like polymer matrix by cyclic mechanical stretching, resulting in reconstructed microstructures and forming highly efficient and stable conductive pathways. Consequently, the electrical conductivities of the resultant composites can be dramatically enhanced by ≈4-8 orders of magnitude and reach ≈104 S cm-1 . The stretch-induced kinematic movements of Ag flakes inside the polymer matrix, together with the reorganization and stabilization mechanisms, are unraveled and validated by the dissipative particle dynamics simulations. This unique phenomenon enables high-performance stretchable conductors to be fabricated with significantly reduced conductive fillers. The printable and stretchable composites presented here hold great promise for use in soft and stretchable electronics, as demonstrated in stretchable light-emitting diode arrays and wearable electronics.

A low cost multi-shapes designed sintering composite paste: A strengthening method of sintered interconnect for die attach in high temperature applications

In this work, we proposed a multi-shape designed Ag-Cu bimetallic pastes for die attach sintering in power electronic packaging. We found a good adaptation of Ag flakes and Cu sphere particles in the sintered microstructure of the multi-shapes pastes. Under the “rolling effects” of the Cu particles, Ag flakes become more compact with larger plastic deformation. Further analysis indicates that sintering properties is highly dependent upon the shapes of the particles. The fracture interface is also highly dependent upon particle shape combination in sintering paste. For Ag flake- Cu sphere combination, more residual sintered masses were found at the fracture interface, which indicate a good strength matching of the sintered bulk and the interface. The sintered die attach connection with optimized particle shape combination perform a maximum shear strength up to 47.42 MPa, which is obtained at a much lower cost than normally used Ag paste.

Property Prediction of Ag-Filled Isotropic Conductive Adhesive through the Analysis of Its Curing and Decomposition Kinetics

In this study, various thermal analyses were carried out on a self-developed and commerce-oriented Ag-filled isotropic conductive adhesive (ICA) and its unfilled matrix resin through which glass transition temperature (Tg) and thermal endurance could be quantitatively predicted. An autocatalyzed kinetic model was used to describe the curing reaction, which was proven to be in good consistency with the experimental data. The activation energies for the curing reaction of the ICA and the matrix resin were determined to be 68.1 kJ/mol and 72.9 kJ/mol, respectively, which means that the reaction of the ICA was easier to occur than its unfilled matrix resin. As a result, the time–temperature profile could be calculated for any Tg requested based on the kinetic model of curing and the DiBenedetto equation. Further, the thermal decomposition stability of the ICA and its unfilled matrix resin were also studied. The activation energies for the thermal decomposition of the ICA and the matrix resin were calculated to be 134.1 kJ/mol and 152.7 kJ/mol, respectively, using the Ozawa–Flynn–Wall method, which means that the decomposition of ICA was easier to occur. The service life of the resin system at a specific temperature could therefore be calculated with their activation energy. The addition of micro-scale Ag flakes did not change the curing and decomposition mechanisms by much.

Biphasic Liquid Metal Composites for Sinter‐Free Printed Stretchable Electronics

AbstractThis work introduces and presents a comprehensive study on a series of biphasic liquid metal (LM) composites that benefit from high conductivity, excellent stretchability, a low gauge‐factor, excellent adhesion to a wide range of substrates, for sinter‐free writing complex stretchable circuits. These trinary material systems are composed of a block‐co‐polymer binder, EGaIn liquid metal, and a microparticle (μP) filler (Ag flakes, Ag‐coated‐Ni, Ag‐coated‐Fe, Ni, Ferrite, or TiC). They combine the fluidic behavior, resilience, and self‐healing properties of LMs, and the printability, adhesion, and elastic integrity of elastomers. Unlike the previous efforts with LM‐polymer composites and printed EGaIn nanodroplets, these composites are intrinsically conductive and do not require any thermal/optical/mechanical sintering. The binary combinations (LM‐SIS, LM‐Ag, Ag‐SIS) are first synthesized and characterized, and then the trinary LM‐μP‐SIS composites are evaluated. This includes analysis of microstructure, surface roughness, conductivity, electromechanical coupling, and LM smearing/leakage during mechanical loading, as well as the examination of the influence of filler particle size and composition. It is found that a binary combination of Ag‐EGaIn or EGaIn‐SIS does not result in the desired properties, and only trinary combination with conductive μP, preferably Ag, results in a printable, stretchable and sinter‐free composite. As an application, a digitally‐printed epidermal sticker for respiration monitoring is demonstrated.

Enhanced Thermal Conducting Behavior of Pressurized Graphene-Silver Flake Composites.

Modern electronics continue to shrink down the sizes while becoming more and more powerful. To improve heat dissipation of electronics, fillers used in the semiconductor packaging process need to possess both high electrical and thermal conductivity. Graphene is known to improve thermal conductivity but suffers from van der Waals interactions and thus poor processibility. In this study, we wrapped silver microflakes with graphene sheets, which can enable intercoupling of phonon- and electron-based thermal transport, to improve the thermal conductivity. Using just 1.55 wt % graphene for wrapping can achieve a 2.64-times greater thermal diffusivity (equivalent to 254.196 ± 10.123 W/m·K) over pristine silver flakes. Graphene-wrapped silver flakes minimize the increase of electrical resistivity, which is one-order higher (1.4 × 10-3 Ω·cm) than the pristine flakes (5.7 × 10-4 Ω·cm). Trace contents of wrapped graphene (<1.55 wt %) were found to be enough to bridge the void between Ag flakes, and this enhances the thermal conductivity. Graphene loading at 3.76 wt % (beyond the threshold of 1.55 wt %) results in the significant graphene aggregation that decreases thermal diffusivity to as low as 16% of the pristine Ag filler. This work recognizes that suitable amounts of graphene wrapping can enhance heat dissipation, but too much graphene results in unwanted aggregation that hinders thermal conducting performance.