Investigation of thermal expansion of PI/SiO2 composite films by CCD imaging technique from −120 to 200 °C

The thermal expansion of the reference sample, pure copper film in the temperature range of −120 to 200 °C was first measured using the newly improved CCD imaging technique for measurement of thermal expansion of thin films. The results showed good accordance with the recommended data given by TPRC (Thermophysical Properties Research Centre, USA) handbook, verifying that the present method is valid for measuring thermal expansion of films. Then, the thermal expansion TE (ΔL/L0) of silica/polyimide composite films with different SiO2 fractions i.e. 0, 1, 3, 5, 8, 10 and 15 wt% prepared using the sol–gel technique was obtained in the temperature range of −120 to 200 °C using the newly improved CCD method and the differential coefficient thermal expansion (CTE) can be deduced by ΔL/L0 ∼ temperature relation. The CTE of SiO2/PI composite films decreased with the increase of SiO2 content and the decrease of temperature. An empirical equation of CTE of SiO2/PI with SiO2 content has been given in this paper.