Role of free volume on breakdown of epoxy nanocomposites: measurement and manipulation

Free volume
$(f_{v})$
, which is strongly associated with the chain mobility and charge transportation in polymer dielectrics, could significantly affect electrical properties. In this paper, free volume of epoxy nanocomposites was effectively reduced by incorporating organically modified
$\mathbf{nano}-\mathbf{Al}_{\mathbf{2}}\mathbf{O}_{\mathbf{3}}$
fillers. Consequently, the highest DC breakdown strength (159.09 kV/mm) was obtained when the filler content was 1 wt%. Fourier transformed infrared spectroscopy (FTIR) results indicated that the filler-matrix interaction brought by the formation of hydrogen bonds as well as covalent bonds were responsible for the free volume manipulation. Images of fracture morphology and analysis by small angle x-ray scattering (SAXS) showed that different degrees of filler-matrix interaction existed when incorporating fillers with varied contents, which as a result gave rise to the successful tailoring of free volume. This paper provides feasible methods for the quantitative measurement of free volume as well as its effective manipulation.