Low Thermal Expansion Composites Prepared from Polyimide and ZrW2O8 Particles with Negative Thermal Expansion

Inorganic/polymer composite films with adjustable small thermal expansion were prepared by incorporating sub-mu m sized particles of zirconium tungstate (ZrW2O8) into aromatic polyimide (PI). ZrW2O8 particles exhibit negative coefficients of thermal expansion (CTE) between -4.8 to -8.7 ppm/K. The cross-sectional SEM images of ZrW2O8/PI composite films indicate that filler particles are homogeneously dispersed in PI matrix without aggregation. The CTEs of these films are linearly decreased with increasing the volume fraction of ZrW2O8. The CTE of a composite film containing 60 vol% of filler is as low as that of metallic copper (17 ppm/K). Assuming that the thermal expansion behavior is three-dimensionally isotropic, PI composite films containing more than 50 vol% of ZrW2O8 could achieve coefficients of volumetric thermal expansion smaller than 50 ppm/K.