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Efficient thermal interface materials (TIMs) are urgently needed for heat dissipation of high-power density electronics. In this study, vinyl polydimethylsiloxane (PDMS) composites with the spatial alignment of carbon fibers (CFs) bridged by Al 2 O 3 particles were fabricated by the flow field. The through-plane thermal conductivity (TPTC) of the composites with 24 vol% CFs and 47 vol% Al 2 O 3 loading reached 38.0 W m−1 K−1. The oriented CFs bridged by Al 2 O 3 acted as the efficient through-plane thermal conductive network. Furthermore, the effects of shape factor (b/a), spatial angle (γ) of CFs, and CF loading (V f) on the TPTC were quantitatively discussed by steady-state finite element simulation combined with micro-computed tomography and machine learning. The positive contribution of the increased V f to TPTC was in competition with the negative contribution of b/a and γ , both of which increased with the increase of V f. Moreover, b/a exerted more negative effects than γ. The PDMS composites demonstrated excellent thermal stability (T d = 407.5 °C, CTE = −55.3 × 10−6 K−1), low compress modulus (1.71 MPa), and hardness (47 (Shore C)), which made them potential candidates for TIMs. This work offers a feasible method to prepare TIMs on large scale and refreshes the thermal conduction mechanism of TIMs by introducing the influencing factors (b/a and γ). [Display omitted] • Efficient heat conduction paths were constructed by spatial alignment of CFs bridged by Al 2 O 3. • The through-plane thermal conductivity of PDMS composites reached 38 W m−1 K−1. • The effect of spatial orientation angle of CFs on the thermal conduction property was revealed. • The PDMS composites with excellent comprehensive properties can be used as TIMs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnetized carbon fibers (MCF) were vertically arranged in silicone rubber (SR) in magnetic field. • The λ of SR composites demonstrated an unusual power-law growth with the increase of MCF. • The o-MCF/SR-9 vol% composite exhibited a high λ of 4.72 W/(m·K) with 2045.5 % enhancement. • A new parameter, "shape factor", was introduced to reveal the heat conduction mechanism. The continual increase in power density and consumption of modern electronic devices calls for high-performance thermal interface materials (TIMs). In this work, silicone rubber composites with vertically oriented magnetic carbon fibers (o-MCF/SR) were successfully prepared via the cast molding and filler orientation upon uniform magnetic field in a vacuum environment. The through-plane thermal conductivity of o-MCF/SR composites showed an unusual power-law growth with increasing MCF loading. At a 9 vol% MCF loading, the o-MCF/SR composite exhibited a maximum through-plane thermal conductivity of 4.72 W/(m·K) with 2045.5 % TCE, about 3.55 W/(m·K) higher than that of SR composites with randomly dispersed MCF (λ = 1.17 W/(m·K), TCE = 431.8 %). To reveal the underlying through-plane heat conduction mechanism of o-MCF/SR composites, finite element simulation combined with classical effective medium theory model and machine learning method was used. A homogeneous unit fiber-filled composite (HUFC) was modelled, and a new parameter influencing the through-plane thermal conductivity, i.e. , shape factor (b / a), was introduced here for the first time. Theoretically, this shape factor was dependent on the filler content and indirectly reflected the assembly of matrix and 1D filler in HUFC fit to a parallel-series hybrid model. Furthermore, a decrease of b / a was practically found with increasing MCF loading, and the dominant series-type assembly gradually transformed to parallel-type assembly of the o-MCF/SR composites. This work not only developed a method to fabricate desirable TIMs that hold great promise for advanced thermal management, but also introduced a new parameter to reveal the underlying mechanism for heat conduction capacity of polymer composites. [ABSTRACT FROM AUTHOR]