Bulk soldering: Conductive polymer composites filled with copper particles and solder

Obtainment and Characterization of Metal-Coated Polyethylene Granules as a Basis for the Development of Heat Storage Systems

The research studied the feasibility of using copper-coated polyethylene granules as a basis for creating efficient heat storage systems. A technology for imparting catalytic properties to a polymer surface by the joint processing of polymer granules and an activator metal in a ball mill with their subsequent metallization in a chemical reducing solution is proposed. The efficiency of copper-coating a polyethylene surface is shown to be largely determined by the activation stage and the assumption regarding the mechanism of interaction of the activator metal with the polymer surface is made. To obtain different amounts of metal on the polyethylene granules, it is proposed that the method of remetallization is used. It was established that the rate of copper ion reduction depends on the number of previous coatings and is determined by the area of interaction of the metal-coated granules with the chemical reducing solution. The obtained metal-coated polyethylene granules were characterized in terms of the viability of using it as a phase transition material for a heat storage system. Using the developed installation that simulates the heat accumulator operation, it was shown that the efficiency of using metal-coated polyethylene granules to create heat storage systems is higher. The copper coating deposited on the polyethylene granules was studied using scanning electron microscopy and X-ray diffraction analysis.

Directed Assembly of Liquid Metal-Elastomer Conductors for Stretchable and Self-Healing Electronics

Growing interest in soft robotics, stretchable electronics, and electronic skins has created demand for soft, compliant, and stretchable electrodes and interconnects. Here, dielectrophoresis (DEP) is used to assemble, align, and sinter eutectic gallium indium (EGaIn) microdroplets in uncured poly(dimethylsiloxane) (PDMS) to form electrically conducting microwires. There are several noteworthy aspects of this approach. 1) Generally, EGaIn droplets in silicone at loadings approaching 90 wt% remain insulating and form a conductive network only when subjected to sintering. Here, DEP facilitates assembly of EGaIn droplets into conductive microwires at loadings as low as 10 wt%. 2) DEP is done in silicone for the first time, enabling the microwires to be cured in a stretchable matrix. 3) Liquid EGaIn droplets sinter during DEP to form a stretchable metallic microwire that retains its shape after curing the silicone. 4) Use of liquid metal eliminates the issue of compliance mismatch observed in soft polymers with solid fillers. 5) The silicone-EGaIn "ink" can be assembled by DEP within the crevices of severely damaged wires to create stretchable interconnects that heal the damage mechanically and electrically. The DEP process of this unique set of materials is characterized and the interesting attributes enabled by such liquid microwires are demonstrated.