Thermal transport in silver-coated polymer sphere composites by the bidirectional 3ω method

Abstract

The bidirectional 3ω method is an electrothermal technique that is commonly used to obtain the thermal conductivity of materials such as liquids, biological samples and pastes. In this work, an epoxy-based adhesive was filled with monodisperse 10 μm polymethyl methacrylate (PMMA) spheres coated with silver thin films (AgPS), such that a metallic network that dominated the thermal transport was formed through the composite. The bidirectional 3Ω method was used to obtain the thermal conductivity of the conductive adhesive at different volume fractions of AgPS. For 50 vol.% AgPS, corresponding to 3.4 vol.% silver, the thermal conductivity was 2.03 ± 0.21 W/m-1K-1. The results show that the thermal conductivity is strongly correlated with the AgPS volume fraction, while maintaining a volume fraction of silver far below commercial silver paste, which has typical filler fractions of 40 vol.\% silver. The results of this work were compared to thermal measurements of the same material by other techniques, and advantages and disadvantages of the methods were finally discussed.