Strawberry Like Micro@nano Hybrid Filler for Thermally Conductive Epoxy Composites

Thermally conductive dielectrics are highly desirable for improving the thermal management capability of power equipment. Traditional dielectrics with high thermal conductivity were prepared by filling spherical micro-sized α-Al
₂
O
₃
or mixture of micro- and nano-sized α-Al
₂
O
₃
into an insulating polymer. However, for a long time, this method suffers from low thermal conductivity enhancement. In this method, a new hybrid filler (μm@nm-Al
₂
O
₃
) with strawberry-shape encapsulation structure was reported for thermal conductivity enhancement of insulating polymers. The new hybrid filler was prepared by two steps: the micro- and nano-sized α-Al
₂
O
₃
fillers were firstly surface-modified by amino-terminated and epoxide-terminated silane coupling agents, and then the encapsulation process was carried out by chemical bond after reaction. At a filler loading of 65 vol% and the volume ratio of nm-Al
₂
O
₃
to μm-Al
₂
O
₃
of 1:4, the thermal conductivity of the epoxy composites with μm@nm-Al
₂
O
₃
exhibit the optimum of 1.9 W/(m·K), and the achieved thermal conductivity enhancement are 12.1%, 16.2% and 21.5% higher when compared with the composites with physical nm-Al
₂
O
₃
/μm-Al
₂
O
₃
mixture, pure μm-Al
₂
O
₃
and pure nm-Al
₂
O
₃
, respectively.