Connecting the Interphase and Morphology of Poly(styrene-3,4-isoprene-styrene)-Carbon Black Composites with Their Performance as Electrothermal Heaters

The interface between polymer chains and filler particles plays a pivotal role in defining the properties of polymer nanocomposites. This study for the first time experimentally connects the nano- and microstructure of polymer–carbon composites to their electrothermal properties and ultimately their performance as electrothermal heaters. Composites of carbon black with poly(styrene-3,4-isoprene-styrene) were investigated, and the effects of polystyrene (PS) blending and carbon black (CB) loading on the interphase thickness, composite microstructure, and electrothermal properties were systematically determined. Quantitative nanomechanical mapping (QNM) via atomic force microscopy (AFM) was used to accurately quantify the interphase thickness, which was correlated with the thermal diffusivity, electrical conductivity, and dynamic mechanical behavior of composites. The results demonstrate that PS blending critically reduced interphase thickness by approximately 60 nm and enhanced thermal diffusivity of 3,4-SIS-16CB composite by 82%, suggesting a reduction in thermal resistance at the interface. The increased thermal diffusivity from PS blending resulted in a 28% increase in the thermal response of prototype electrothermal heaters (10.4 °C min–1) and a 21% increase in steady-state temperature (110 °C) compared to the nonblended composite. This investigation offers a deeper understanding of how the polymer–CB interphase structure can be engineered to improve the efficiency of next-generation polymer nanocomposites for advanced electrothermal applications.