Tropocollagen-Inspired Hierarchical Spiral Structure of Organic Fibers in Epoxy Bulk for 3D High Thermal Conductivity

Abstract

Polymers are usually considered thermal insulators; however, significant enhancements in thermal conductivity (k) have been observed in oriented fibers and films. Despite being advantageous in real-world applications, extending the linear thermal-transport advantage of polymers into the 3D space in bulk materials is still limited due to the spatially interfacial phonon-conduction barriers. Herein, inspired by the structure of tropocollagen, it is discovered that weaving hierarchically arranged poly(p-phenylene benzobisoxazole) (PBO) fibers with a spiral configuration into an epoxy matrix can yield a 3D continuous thermal pathway. This achieves both a through-plane k of 10.85 W m⁻¹ K⁻¹ and an in-plane k of 7.15 W m⁻¹ K⁻¹. Theoretical molecular simulations in combination with classical nonlinear modeling attribute the above spatially thermally conductive achievement to not only the hierarchical molecular, spiral and weaving structure of PBO, but also the noncrystalline chains that carry overlapping phonon density of states, thus thermally bridging adjacent high-k crystals in the PBO fiber. Consequently, the interfacial thermal resistance among high-k PBO crystals is suppressed to be on the order of 10⁻¹⁰ m² K W⁻¹ in both the through-plane and in-plane directions. Other advantages include being lightweight, mechanically strong, flexible, and non-combustible. This material creates opportunities for organic polymers in high-performance thermal management applications.