Flexible Thermal Interface Materials with High Dispersion of Liquid Metal in Polyurethane induced by Sodium Alginate Microcapsules

As electronic devices advance towards higher performance and miniaturization, the demand for flexible thermal interface materials has significantly increased. Liquid metal (LM) is considered an ideal conductive filler of polymer materials due to its superior thermal properties and fluidity. However, LM’s electrical conductivity makes achieving insulation in LM-polymer composites with high LM content challenging. This study introduces a novel method for preparing uniform dispersion, high thermal conductivity yet non-conductive LM composite films. This method involves pre-coating LM microspheres using sodium alginate microcapsule before incorporating them into a polyurethane matrix. This approach effectively overcomes the inherent challenges associated with the uniform distribution of LM in polymers, such as leakage and uneven dispersion, thereby significantly enhancing the stability and filler loading of LM. Even when stretched, the LM microcapsules will not be broken. Through this technique, we successfully increased the LM loading to 80 wt%, while preserving the mechanical integrity and electrical insulation properties of the composite. The thermal conductivity of the composite increased from 0.17 W/mK to 1.59 W/mK, significantly surpassing that of unmodified polyurethane. The electrical resistivity was measured as 1.1 GΩ·m under normal conditions and remains high even under 300% elongation. Furthermore, the surface properties of the composite have been investigated, revealing that its hydrophobicity decreased as the microcapsule content increased. This study adeptly achieves a synergistic balance between high filler loading and the enhancement of thermal, electrical, and mechanical properties, making it ideal for the demanding specifications of high-performance electronics and advanced energy systems.