Understanding heat transport in hierarchical materials is essential for the rational design of next-generation thermal management systems. In this study, we utilize a combination of electrospinning and functionalization techniques to fabricate a series of polystyrene (PS) nonwovens with defined variations in fiber alignment and fusion, as well as functionalization with metals. Using lock-in thermography, we analyze in-plane thermal transport with directional sensitivity and correlate the results with morphological characteristics. We show that increasing fiber alignment enhances thermal anisotropy only up to a certain threshold, beyond which the quality of interfiber contact becomes the dominant factor. The incorporation of nonpercolating silver nanowires is only effective when phonon scattering is minimized. Otherwise, fiber boundaries significantly limit the potential transport enhancement offered by these costly additives. In contrast, copper coatings form percolating networks that markedly enhance thermal transport, yet they remain governed by the global architecture of the fiber network. Altogether, this work experimentally highlights that minimizing phonon scattering and controlling structural features are more critical than maximizing fiber or filler alignment. The insights contribute to a deeper understanding of heat conduction in fibrous systems and offer guidance for designing such materials with targeted performance.
Klein et al. (Mon,) studied this question.