Adding heterogeneous fillers with high thermal conductivity (TC) to polymer has been recognized as an effective way to increase the effective thermal conductivity (ETC) of polymer composites. Extensive researches have been conducted on the ETC of composites with heterogeneous fillers. However, the heat transfer enhancement mechanism of heterogeneous fillers remains unknown, and the combined effects of filler size, filler contact, interface thermal resistance (R_c) and other parameters on the ETC have not been explored. In this study, above combined effects are investigated. The results show that the filler contact and R_c are the key factors determining the ETC. The ETC of composite with filler contacts reaches 2.35 at filler content of 25%, which is 11.9% higher than that without filler contacts. The ETC also strongly depends on the R^*_c (dimensionless form of R_c) ratio (R^*_c1/R^*_c2) between two fillers, with it becoming asymmetrical when the amount of R^*_c(R^*_c1 + R^*_c2) is larger. The ETCs decrease with the increase of R^*_c1/R^*_c2 when the R^*_c1/R^*_c2<1, while they increase with R^*_c1/R^*_c2 when the R^*_c1/R^*_c2>1. When R^*_c1 + R^*_c2 is a constant, the ETC increases with the competing effects of R^*_c. The models with filler contacts exhibit higher accuracy than other classical models in calculating the ETC across the entire range of filler content.

In this study, a novel methodology for the fabrication of gradient porous structures is introduced, predicated upon the phase evolution characteristics of immiscible polymer blends. Initially, a comprehensive flow-phase field dynamics model is developed. This model couples the principles of phase field theory and the dynamics of fluid flow to the two-phase evolution process, facilitating a numerical simulation of the phase evolution. Subsequently, the phase field parameters of model are determined and combined with the temperature field, thereby enabling a targeted and controlled fabrication of gradient porous structures. Finally, the efficacy and practical applicability of the proposed methodology are substantiated through the construction of illustrative examples. This approach, as delineated herein, provides a robust framework for the efficient design and realization of intricate, interconnected gradient porous structures with potential applications in various scientific and engineering domains.