Plasma‐in‐Liquid Surface Modification of AlN Filler for Thermally Conductive Composites

ABSTRACT The recent trend of dense circuit integration in flexible electronic devices has intensified heat generation, making thermal management a critical issue. Consequently, there is a high demand for flexible and thermally conductive insulating materials. Composite elastomers with high‐thermal‐conductivity inorganic particle fillers, such as aluminum nitride (AlN), are promising materials. However, poor filler dispersion often reduces composite mechanical performance, making it difficult to simultaneously achieve high thermal conductivity and good mechanical properties. In this study, a plasma‐in‐liquid treatment was applied to AlN particles, and its influence on particle dispersion and composite properties was investigated. Fourier transform infrared spectroscopy and X‐ray diffraction analyses confirmed that the AlN particles retained their original chemical structure and crystallinity after plasma treatment. The plasma‐treated AlN showed improved dispersion in the polymer matrix and enhanced mechanical properties compared with untreated AlN. At a filler loading of 50 wt%, the composite exhibited a thermal conductivity of 0.5 W/mK, far exceeding the Maxwell‐model prediction, and a Young's modulus of 10 MPa, approaching the theoretical lower value for the composite. The composite material also exhibited a stress–strain response close to ideal rubber elasticity, consistent with the improved filler dispersion observed experimentally. These results demonstrate that composites containing plasma‐treated AlN can simultaneously exhibit improved particle dispersion, mechanical softness, and high thermal conductivity.