Enhanced Thermal Conductivity in Polyimide/Silver Particle Composite Films Based on Spontaneous Formation of Thermal Conductive Paths

A series of polyimide (PI)/silver composite films incorporating μm-sized metallic silver particles (Ag-MPs) were prepared using matrices of sulfur- (SD), fluorine- (TF), and silicon-containing (SIM) PIs as well as an immiscible blend of SD- and TF-PIs (b-SF). The thermal conductivity (λ⊥) of the composited films accords well with the calculated value (λcal) based on the Bruggeman model below the particle contents (φ) of 30 vol%, whereas the composite films of SD/Ag and b-SF/Ag exhibited extraordinarily larger λ⊥ values than λcal in the range of φ>30 vol%. Moreover, the λ⊥s of SD/Ag films with uniform dispersion of Ag-MPs are almost equivalent to those of b-SF/Ag films in which Ag-MPs are selectively dispersed in the SD phase. In contrast, the λ⊥s of SIM/Ag films with homogeneous dispersion accord well with the λcal and much smaller than those of SD/Ag and b-SF/Ag. These facts indicate that effective thermal conductive paths were spontaneously generated in SD/Ag films as well as in b-SF/Ag films.