Visualisation of conductive filler distributions in polymer composites using voltage and energy contrast imaging in SEM

Semiconductive composites have been examined using advanced scanning electron microscopy (SEM). For the first time, voltage contrast and energy contrast between the conductive filler and the polymer matrix have been revealed using a secondary electron detector placed inside the lens system and an energy selective backscattering detector respectively. Critical parameters, including loading level, distribution, dimension and shape of conductive fillers, correlating to the electrical conductivities of the composites, have been investigated and quantitatively determined. These parameters are essential for performance predictions, product quality control and new product development. The volume fractions of the conductive fillers in the two investigated composites were determined as 20.9% and 14.2% respectively. Higher frequency of distribution distance between the conductive filler aggregates within the ranges of 20-100 nm was revealed for the composite with volume fraction of 20.9%. The aggregates of conductive fillers showed mainly branched shapes. The information obtained provides further insight into the conductivity mechanism of conductive filler loaded polymer composite.