The Synthesis Of 3D Micro-/Nano-Sized Fractal Ag Dendrite And Its Application In Electrically Conductive Composites

Recently, fractal metallic dendrites(FDs) have been drawing more attentions in broad research fields. Due to their unique geometric, chemical, and surface plasmon resonance properties and antimicrobial and biocompatible characteristics, the FDs have great potential in areas such as electronics, chemistry, biotechnology, medicine, medical devices and commodities etc. In the information era, the FDs with abundant nanostructures are high-tech functional materials, which may have significant influence on electronic information, novel printing technology and flexible displays.At present, the most widely used conductive fillers of electronically conductive composites(ECCs) are 0-D Ag particle and 2-D Ag flake. The Ag particle-based ECCs have high conductive percolation threshold. As for Ag flake-based ones, the shear force during printing and dispensing processes may induce alignment of the fillers, causing anisotropy of the composite with weakened conductivity normal to the filler-aligned direction(s). Enormous efforts have been made to improve the percolation efficiency by mixing fillers of different sizes and shapes and by using chemical surface activations. As compared, simple mixing of three dimensional(3-D) metallic fillers in a polymer matrix may become one of the most beneficial technologies featured with simplification, quality control, and cost reduction for ECC applications, so as to improve the 3-D percolation ability of ECCs essentially.To date, the FDs have not been used in electronic printing and packaging yet, the main reasons are as follows:(1) people have not found an efficiently scalable synthesis method to obtain the proper micro-sized and mono-dispersed FDs;(2) The lack of research on the growth mechanism of FDs brings more fundamental challenges to the precise morphology control of FDs.In this work, we choose NH2 OH as the reductant and surface agent to reduce the Ag NO3 at ambient temperature. The synthesis condition is accurately controlled to critically adjust the morphology, size and reproducibility. We use the Density functional theory(DFT) to systematically investigate the selectively adsorption of NH2 OH on Ag facets and the growth mechanism of FDs. Benefited by the low temperature sintering property, we apply the FDs as conductive fillers for ECCs to obtain an ultralow percolation threshold. And then we investigate the percolative ability and the percolation mechanism of FDs based ECCs via experiments, percolation theory prediction and 3-D Monte Carlo simulation.To evaluate the reliability of FDs based ECCs, we carry out the laser scribing process for fine circuit patterning in the flexible displayers. Moreover, the reliability tests results(bending test, adhesion test and 85oC/RH reliability test) can prove that the FD based ECCs have sufficient reliability for practical applications. The mechanism of laser etching on the FD based ECCs and the energy transformation are discussed.