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

Abstract

Inorganic/polymer composite films with adjustable small thermal expansion were prepared by incorporating sub-μm 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.