Iodine-Induced Microphase Separation Controls the Flow Behavior and Electrical Conductivity of Silver-Filled Polymer Composites

Silver-filled electrically conductive polymer composites play a crucial role in various fields of electronics, such as die attach, chip packaging, solar cell interconnection, and soft printed electronics. This study explores the use of iodine-induced microphase separation of silver particles to achieve high electrical conductivity in the corresponding polymer composites at low particle loading, thereby preserving this precious resource. Three iodine salts─1-butyl-3-methylimidazolium iodide, potassium iodide, and sodium iodide─were directly mixed into thermoplastic polyurethane solutions with varying contents of micron-sized silver particles. This resulted in a paste-like suspension texture, indicating the formation of a percolating particle network already in the wet state. The electrical conductivity of the corresponding dry films improved from 10^–5 S/cm without added iodine to 500 or 2600 S/cm at 12 or 20 vol % silver, respectively, irrespective of the iodine type. Thermogravimetric analysis and infrared spectroscopy confirmed that iodine removes lubricants from the silver particle surfaces, facilitating stronger particle attraction. Accordingly, scanning electron microscopy revealed iodine-induced microstructural heterogeneities. These findings highlight the potential of iodine-modified, silver-filled polymer solutions as a straightforward, cost-efficient approach to producing high-performance conductive materials for electronic applications.