Conductive copper nanoinks can be used as a low-cost replacement for silver and gold nanoinks that are used in inkjet printing of conductive patterns. We describe a high-throughput, simple, and convenient method for the preparation of copper nanoparticles in aqueous solution at room temperature. Copper acetate is used as the precursor, hydrazine as the reducing agent, and short chain carboxylic acids as capping agents. The concentration of the carboxylic acid plays a key role in the preparation of such copper nanoparticles. Stable copper nanoparticles with a diameter of less than 10 nm and a narrow size distribution were prepared when high concentrations of lactic acid, citric acid, or alanine were used. Thermogravimetric analysis results showed that any lactic acid or glycolic acid adsorbed on the surface of the copper nanoparticles can be removed at a relatively low temperature, especially, glycolic acid, which can be removed from the surface at about 125 °C. Highly conductive copper films prepared using lactic acid and glycolic acid as capping agents were obtained by drop coating a copper nanoparticle paste onto a glass slide followed by low temperature sintering. The electrical resistivity of the copper film using glycolic acid as the capping agent was 25.5 ± 8.0 and 34.8 ± 9.0 μΩ·cm after annealing at 150 and 200 °C for 60 min under nitrogen, respectively. When lactic acid was used as the capping agent, the electrical resistivity of the copper films was 21.0 ± 7.0 and 9.1 ± 2.0 μΩ·cm after annealing at 150 and 200 °C for 60 min under nitrogen, respectively, with the latter being about five times greater than the resistivity of bulk copper (1.7 μΩ·cm).
Metal transparent conductive films (TCFs) have received increasing attention in various flexible electronics. However, there are two crucial issues that need to be addressed: (1) strong adhesion between metal TCFs and the flexible substrates and (2) high conductivity with short treatment time and low process temperature, simultaneous with high transparency. In this paper, a site-selective electroless plating combination with poly(dopamine) modification is demonstrated to fabricate a new high performance transparent conductor composed of a periodic two-dimensional silver network on a heat sensitive flexible substrate at room temperature. The TCF reveals an extremely high ratio of DC to optical conductivity (σ(DC)/σ(Op)) value in the range of 350-1000 for various fabricated silver grid films. It also exhibits particularly strong adhesion, which can resist ultrasonic treatment in water or organic solvent for several hours. Its reliability (stable for at least 1440 h during 85 °C/85% RH aging) meets the essential requirements for microelectronic applications. Using this method, we obtain silver grid film on a flexible polyethylene terephthalate substrate with optical transmittance of 91% and sheet resistance of 8 Ohm sq(-1), which is comparable to or better than the commercially available indium tin oxide.
High performance epoxy resins have attracted much research interest in the last decades. Herein, two novel epoxy monomers containing cycloaliphatic hydrocarbon, 1,4-bis(4-(N,N-diglycidylamino)phenoxy)cyclohexane (CyhEP) and 1,3-bis(4-(N,N-diglycidylamino)phenoxy)adamantane (AdaEP) were synthesized and characterized. They were cured with 4-methylhexahydrophthalic anhydride (MHHPA) to prepare the highly crosslinked thermosets. Both epoxy resins show good thermal stability (T d5 > 300 8C), high glass transition temperature (> 200 8C), and high storage modulus (> 3.2 GPa) due to their highly crosslinked structure. The AdaEP/MHHPA resin shows a low dielectric constant (3.4 at 1 MHz) because of the introduction of bulky rigid adamantane into the polymer.
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