Direct Experimental Validation of Parallel Thermal Transport in Fiber-Aligned All-Organic Composites

Highly aligned polymer fibers provide continuous pathways for directional thermal conduction in all-organic composites, yet quantitative prediction remains limited by the lack of independently measured constituent-fiber thermal conductivity. Here, we study polydimethylsiloxane (PDMS) composites reinforced with commercial ultrahigh-molecular-weight polyethylene (UHMWPE), poly(p-phenylene benzobisoxazole) (PBO), and Kevlar fibers. The axial thermal conductivities of individual fibers and PDMS are measured independently and used, together with fiber volume fraction, as direct inputs to a parallel model. The model quantitatively captures the axial thermal conductivity of all three aligned fiber/PDMS materials over a range of fiber volume fractions. Molecular dynamics simulations further reveal distinct phonon-transport characteristics among crystalline PE, PBO, and Kevlar and support the parallel thermal transport trend. These results establish a quantitative framework linking constituent properties and continuous pathway architecture to axial thermal conduction. The UHMWPE-PDMS composite achieves 26.66 W m-1 K-1 while retaining low density, flexibility, electrical insulation, and thermal stability.