Positron annihilation studies of free volume and dielectric constant in fluorine-containing polyimides

Abstract

Positron annihilation study of the fractional free volume and dielectric constant in fluorine-containing polyimides is conducted. Fluorine substitution in these polyimides lowers dielectric constant by a combination of free volume and polarizability effects. Positron annihilation allows direct measurement of the free volume, and thus allows more direct estimates of the role of free volume change upon fluorine substitution. The free volume contribution to decreases in dielectric constant is about 50% for all three F/H pairs studied.