Effect of particle size and shape on positive temperature coefficient (PTC) of conductive polymer composites (CPC) — a model study

• Model polymer composite system to study the effect of the filler size and shape on the positive temperature (PTC) intensity.
• PTC intensity increases with increasing filler size, both for spherical and flake-like conductive filler
• PTC intensity increases with decreasing filler content, both for spherical and flake-like conductive filler.
• The concept of ‘robustness’ of the conductive filler network can phenomenologically explain the observation.

More than four decades since the discovery of the positive temperature coefficient (PTC) effect in conductive polymer composites (CPC), many fundamental aspects related to this phenomenon are still poorly understood, though there is consensus on the important contribution of the mismatch of the thermal expansion coefficients of the polymer matrix and filler. The aim of this paper is to study a model system able to explain the PTC effect and more in particular the effect of the filler size and shape on the PTC intensity of a CPC. Silver coated glass particles (spheres and flakes) are used as model conductive fillers due to the ease in controlling uniform size and shape. For the first time in a controlled system it is demonstrated that the PTC intensity increases with increasing filler size and with decreasing filler content, both for spherical and platelet-like conductive fillers.

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