Textile is a kind of emerging substrate for wearable printed electronics to realize recyclable smart products by versatile and low-cost screen printing. The high temperature sintering step is necessary to get high surface electrical conductivity, whereas most of the common fabrics have poor temperature endurance. Meanwhile, both rough surface and porous structure of fabrics are not beneficial to obtain high-resolution and high-quality circuits. In this work, the ultraviolet (UV) curable conductive inks with lowtemperature and short-time curing were developed for screen-printing e-textiles, and the rheological behavior of conductive inks with different polymer contents was characterized in order to determine the ink formulation suitable for screen printing on fabrics. To demonstrate the usability of the developed ink in fabricating e-textiles, the conductive lines with different widths as well as the antenna for UHF RFID tags were screen-printed on plain nylon-woven fabrics. The geometric morphology and the electrical properties of the printed conductive lines were evaluated. The results showed that the screen-printed conductive lines have a minimum line width of 0.2 mm, highest conductivity of 6.02 × 10 6 S m −1 , and good bending endurance at a bending radius of 5 mm. Also, the feasibility of UV curable conductive ink for a fabric-based electronic device was confirmed by the screen-printed antenna of UHF RFID tags, and the reading distance after five cycles of washing is still over 3.0 m. Generally, this work developed a kind of low-temperature curing ink characterized by direct screen printing on common fabrics and high electrical conductivity after curing, and it will facilitate the use of textiles as the screen-printed substrates for flexible and wearable electronic devices.
Conductive lines are essential for the integration of electronic devices into fabrics, and their direct screen printing on fabrics is a promising, simple and low-cost method for mass-manufactured textile-based conductive lines. However, the intrinsic porous structures and texture characteristic of textiles complicate the diffusion and penetration of conductive ink, and will deteriorate the printing precision and electrical performance of conductive lines. To establish the relationship between the surface characteristics (i.e. porosity, roughness, contact angle) and printing precision as well as electrical performance, the screen-printed conductive lines on six different nylon woven lining fabrics were examined and compared. Moreover, to study the printing precision and the minimum printable line width on woven lining fabric, conductive lines with different widths were screen printed. The results showed that the fabric substrate with the smallest pore size and roughness shows a higher printing precision and lower electrical resistance of screen-printed conductive lines. Relatively, the dynamic contact angle and wetting time of ink on the surface of the fabric have a significant effect on the printing precision. Therefore, the surface structure of the fabric substrate determines to some degree the printing precision of conductive lines, the printable minimum line width and its electrical properties. It is believed that these findings will provide some important support for screen printing flexible electronic devices on woven textiles.
All-in-one supercapacitors are considered to be promising due to their advantages of flexibility and structure stability. However, the sophisticated and precise manufacturing processes and difficulty of series/parallel integration hinder their application and development. Herein, cost-effective all-in-one fabric-based supercapacitors (all-in-one FSCs) are fabricated by utilizing the facile screen-printing technique and multiwalled carbon nanotube (MWCNT) electrodes. The MWCNT electrodes are constructed on the gel-electrolyte-soaked fabric that simultaneously serves as separator and electrode substrates. The as-prepared all-in-one FSC exhibits better capacitive behavior and rate capability and lower internal resistance than traditional sandwiched fabric-based supercapacitors (sandwiched FSCs). Moreover, due to the simplified structure and interface interaction, the all-in-one FSC shows excellent flexibility and stability even under dynamic bending cycles with a relatively high strain rate of 20% s–1. This work also demonstrates the seamless series/parallel integration scheme of all-in-one supercapacitors by designing the screen-printing patterns instead of using metal wires. The proposed fabrication process and series/parallel integration scheme definitely improve the portability of integrated supercapacitors and potentially contribute to the large-scale production and application on wearable electronics.
Cure kinetics control of epoxy resins is critical for the realization of many structures and processes and is often manipulated by catalyst design. We here show an example of switchable Lewis base catalytic activity through ligand-controlled metal coordination. Divalent first-row transition-metal (Co, Ni, Cu, Zn) β-diketonates with methyl or trifluoromethyl end groups have found distinguished thermal latent curing behaviors in triphenylphosphine (TPP)-catalyzed epoxy resins, namely, a deceleration pattern for metal acetylacetonates (acac2) and an inhibition pattern for metal hexafluoroacetylacetonates (6Facac2). Comparative analysis exposed the major initiation mechanism as phosphine attack on epoxide rings, where the phosphine reactivity was regulated by metal coordination whose strength depends on the original diketone ligands. TPP further stabilized the metal chelates and suppressed their dissociation. Feed ratio studies of Co(II) chelates revealed an equilibrium built upon TPP, metal chelate, and the formed passivated complex through numerical analysis. Further, temperature dependence of the equilibrium constants suggested a reversed metal-base affinity evolution of the two chelates during heating, which determines the equivalent TPP concentration. Chemical and thermal characterizations on the formed complexation states identified structural changes during high-temperature treatment and, along with density functional theory (DFT) calculation, verified the Co–P binding energy that marks the TPP “effectiveness” in each stage to catalyze epoxy cure. It was found that the competition between incoming phosphine and original diketone ligands, depending on the basicity of the latter, dictates the initial relative affinity between metal and phosphine, while beyond phosphine ligand stabilization, the diketone ligand dynamics at elevated temperatures were accompanied by the respective Co–P affinity change. Across different metals, the deviation from the “natural order” in metal-phosphine affinity can also be qualitatively understood from the ligand competition concept, where the same ligand effects on the field stabilization schemes are expected as the distinctions caused by ligand fluorination were consistent throughout d7–d10 metal cations. The knowledge gained from this work could benefit future design of thermal latent catalysts and shed light on the capability of Lewis base reactivity control through adjusting transition-metal coordination spheres.
Nowadays, the chipless radio frequency identification (RFID) tag is attracting significant attention owing to its immense potential in tracking. However, most of the chipless tags are fabricated on hard printed circuit boards, and the wearable fabric-based chipless tag is still in the research stage. In this paper, a symmetrical 3rd L-shaped multi-resonator wearable chipless RFID tag is designed and screen-printed onto fabric. In order to investigate the influence of the non-uniform conductive layer on the signal transmission at high frequency, the surface and cross-sectional topographies of the printed conductive film are analyzed and the frequency response characteristics are simulated and measured. The obtained results show that the common fabric can be used as the substrate to screen print the L-shaped multi-resonators of the chipless RFID tag, and the quality of the screen printed line, especially a narrow line, significantly affects the radio frequency performance. For the screen-printed 3rd L-shaped stub resonators, the relative frequency shift compared with the simulation results are 0.99%, 0.88% and 2.26%, respectively. Generally, the surface morphology of fabric and screen-printed precision are critical in improving the performance of L-shaped multi-resonators.
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