Linking surface fractality and roughness to seebeck response in SWCNT-reinforced polyester composites

Abstract

In this study, pure polyester and 2 wt.% single-walled carbon nanotube (SWCNT)-reinforced composites were fabricated to elucidate the relationship between surface heterogeneity, fractal morphology, and thermoelectric (TE) performance. Scanning electron microscopy images were digitized and quantitatively analyzed using fractal and statistical approaches to determine fractal dimension, surface coverage ratio, cluster density, and roughness parameters. The incorporation of SWCNTs resulted in a statistically significant increase in fractal dimension from 1.84–1.88, accompanied by enhanced surface coverage and cluster density, indicating increased morphological complexity and network formation. Carbon nanotube (CNT) addition also led to higher surface roughness, reflecting the development of a spatially interconnected nanotube structure. TE measurements revealed positive Seebeck coefficients, confirming p-type conduction behavior. Although the Seebeck coefficient decreased with increasing electrical conductivity in the percolative regime, the power factor improved due to the dominant contribution of enhanced charge transport. These results demonstrate that CNT-induced surface heterogeneity and fractal network evolution play a decisive role in modulating electrical and thermoelectric performance in polyester-based composites.